Thorn Cycles Forum
Community => Thorn General => Topic started by: Danneaux on June 11, 2012, 08:31:32 pm
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Hi All!
My Sherpa developed a severe shimmy problem under heavy load. Despite applying my best efforts and calling on the collective wisdom of the Forum, the problem persisted. Robin Thorn, his designer and "test pilot" Andy Blance, shipping supervisor Cath Colenso, and the entire Thorn staff became involved in addressing the problem and made every possible effort to help and assist me. They communicated with me nearly every business day by email, and at their expense shipped a Thorn EXP rack and a replacement front fork in a different offset in an attempt to resolve the problem with this one rogue Sherpa. When it became evident the problem could not be addressed, they offered to replace my bike with a Nomad Mk2, since the Sherpa Mk2 was no longer available and the Sherpa Mk3 has a lower load rating insufficient for my expeditionary needs.
My acceptance of their offer did not mean the end of their help and assistance. They volunteered to test the new bike to be certain it would meet my requirements, and Andy loaded the bike with my maximum expected load and set off to do just that, as Robin followed in the company van and Cath caught it all on video, available for viewing here: http://www.facebook.com/Touringbikes
As I write this, the Sherpa is boxed in my livingroom, awaiting collection by Thorn for a complete analysis of the problem. This is simply outstanding customer service, and we can all rest easier knowing that Thorn stand behind their warranty and have gone far beyond the efforts of any other bike-maker I can imagine. My sincere thanks and gratitude to Thorn the company, to Robin Thorn himself, to Andy, to Cath, and to the entire staff for an outstanding job. I can't begin to describe the incredible care and detail with which the new bike was assembled, packed, and shipped; it is simply perfect, and performs as one would expect -- like a Thorn.
I have decided to leave this thread intact, as the efforts I went to in attempting to resolve the shimmy might prove helpful to others investigating any similar problem on their own bikes of any make. In doing so, I want to express my heartfelt "Thanks!" to each and every contributor and correspondent who tried so hard to help resolve my problem and supported my efforts to fix it on my own before I notified Thorn and asked for their help.
A summary of Thorn's efforts begins on Page 9 of this thread, followed by an explanation of Andy Blance's test-load and general-load recommendations in his own words on Pages 9 and 10. I thought them to be of such value, I posted them as a standalone sticky post here for easy reference: http://www.thorncycles.co.uk/forums/index.php?topic=4515.0
When and if the cause of my Sherpa's shimmy can be found, I will append it to the end of this thread.
And now, onto the original thread, as it played out...
All the best,
Dan.
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Hi All,
Sherpa has developed a severe shimmy problem, and I need to call upon the Collective Hive Mind of the Forum for help.
Earlier, I loaded Sherpa in a number of fully-loaded touring configurations and took him on long day rides. No problem. Solid as a rock.
Today, I loaded everything up and planned to take a shakedown tour to the mountains. Big problem. The bike was so unridable I had to walk it down 6% hills, which was no fun in racing cleats. I have given up on the shakedown tour, and am back at home to try and sort things out.
I made a quick little table and attached it as a .jpg so you can see what I carried and where. Compared to a desert crossing, I did not have any water in the MSR dromedary bag atop the rear rack. I would normally carry 6l there, so that is 13.23lbs/6kg saved there. As it was, my entire load *on* the bike was 82.09lb/37.24kg. Add my 172lb/78kg and the bike's weight of 42lb19.05kg (1.4lb was added with the ring-lock) and the total on the tires is 296.09lb/134.30kg as I rode it today. Earlier, he had worked fine with a load of 103lb/46.72kg carrying the extra water.
Here's what I found:
1) The shimmy was not always present. It never appeared below 9mph/14.5kph. It manifested from about 10-15mph/16-24kph, and then subsided until about 18mph/29kph and was present thereafter. It was horrible at 25mph/40kph and I once took the bike up to 45mph/72kph and really wished I hadn't.
2) The shimmy was worse when I removed one hand from the handlebars.
3) The shimmy manifested as a sine wave in the top tube, with an amplitude of about 1.5cm from center, and at a frequency of about 2.7 cycles/second. It was about as quick as you can say "Wogga-wogga-wogga" in one second.
4) Once started, the shimmy was self-perpetuating within a speed range. It didn't quiet down after a couple cycles, but just kept going.
5) I tried riding loose, tense, and hanging on for dear life; none made a difference. Neither did gripping the top tube with my knees or a closed hand.
6) I was riding only on pavement, but road surface did make a difference. Not the immediate surface, but the smoothness. Wavy pavement triggered the shimmy immediately.
Here's what I tried:
1) Adjusted tire pressure. Up to 55psi F/R. then down to 40 F/R. Then differentially, 55/40 and 40/55. No difference.
2) Moved both steerer mounted 1l bottles to rear rack-top. Very slight positive difference, but not enough to matter.
3) Emptied both steerer mounted 1l bottles. Very slight positive difference, but not enough to matter.
4) Emptied all three 1.5l bottles on frame. Very slight positive difference, but not enough to matter.
5) Removed and stashed handlebar bag in bushes. Very slight positive difference, but not enough to matter.
6) Re-oriented rack-top load F/R and then redistributed it side-to-side. Very slight positive difference, but not enough to matter.
7) Checked headset; properly adjusted.
8 ) Checked wheels; properly tensioned and true.
9) Checked tires; properly seated and true except for the usual slight wander of the tread cap.
10) All bags solidly mounted and noise-free.
11) All racks solidly mounted and noise-free. No discernible sway in either rack. The shimmy involved mostly the top tube from what I could see. I took a video, but gave up after a few seconds 'cos riding with one hand was almost impossible. Later, I may try posting the two clips I took.
12) Before emptying my water, all the bottles were full and slosh-free.
13) All heavy objects were placed toward the center of the bike L/R and F/R to keep the polar moment of inertia as low as possible. The load was well-balanced and well-placed.
14) Sherpa's frame appears sound in every way, with no bends, misalignment, or broken welds. I have never taken a fall on him, nor has he toppled over while parked. And yes, the wheel quick-releases are tight.
15) The packing scheme is the same as in earlier test runs, except for lacking the extra 6l of water in the MSR Dromedary atop the rear rack. Earlier, he did fine with a load of 103lb/46.72kg carrying the extra water.
Since everything is a known weight and modular, I think I will add or subtract modules as needed and then race up and down the street in front of the house to see if there is a difference. I've rearranged my schedule for the Big Tour, and right now, I can't take it, so I'm up against the calendar. I love the bike, have a sizable investment of time and money in it, and need to make it workable if at all possible.
This is essentially what happened to my Miyata 1000LT *after* my Great Basin tour in 2010, and led to my purchasing Sherpa. I carried 77lb/35kg of load then, and used the Thorn Low-Loader in front. I broke a weld on the last strut of my alu rear rack and replaced it with the Surly Nice (Rear) rack before retiring the bike due to the shimmy problem, which by that time manifested even without a touring load. Both racks were transferred to Sherpa and appear sound and solid in every way.
My thanks to all in advance. I do so hope I can come to a resolution that will resolve the problem and allow me to use the frame for its intended purpose, as it did so well on earlier test runs. I'm baffled.
Best,
Dan.
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rear rack bolt loose? Happened to me once, in a similar way to your excitement - so it is just a thought.
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Apologies if this posts twice. My first attempt has fallen into a black hole. This is probably not the answer Dan but I thought I had to mention it. My fully loaded Raven Tour had a wobble at full load 40kg but not at 10kg
less. It turned out to be the Pitlocks needed tightening. No problem at all until that last 10kg was added. I know you don't use them but I thought I would mention it. Good luck with your detective work.
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Excellent ideas!
Checked the rack bolts, Pavel; all as tight (and LocTite!) as can be.
Checked the SON28 bolt-on front skewer and the Shimano Deore rear Q/R skewer, Richie. Both are secure to specs.
Just did a number of quick runs in front of the house, carrying *only* the LF pannier, the RF pannier, and the HB bag @ 31.95lb/14.49kg. The bike was as thoroughly pleasant and vice-free as when it is completely unladen. I could happily tour like this. Steady as can be right up to 25mph/40.23kph with both hands on the bars, one off, and both hands off, sitting upright, with hands on the tops, on the brake hoods, and on the drops. Steady and safe as houses, no hint of shimmy, even when I horsed around on the bike (leaning to one side, moving around in the saddle, etc).
Onward.
Best (and thanks!),
Dan.
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Okay...
Just added the 2 steerer-mounted waterbottles at 1l each for a total of 4.46lb/2.02kg
*and*
the 3-1.5l bottles to the downtube and seat tube cages, for another 10lb/4.54kg
Total additional, 14.46lb/6.56kg.
Grand total with the two front panniers and handlebar bag is 46.41lb/21.05kg, all on the front wheel and mid-frame.
Handling definitely felt heavier, but absolutely no sign of shimmy, and was repeatedly able to ride no-hands and in all positions at 25mph.
Correlation does not equal causation, but this makes me hopeful the problem is not solely due to heavy weight at the front or midframe. I suspect the shimmy may be due to the load atop the rear rack (tail wagging the dog effect or -- same frequency -- the 1994 Ertl "Jibber Jabber" doll effect, see: http://www.youtube.com/watch?v=l-Cey1t6ZEA ), but will wait to see what the qualitative and empirical data say. It may well be the shimmy is induced by an additive and synergistic effect, so I will also strip the bike and start adding weight from the rear moving forward.
More in a bit...
Best,
Dan.
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Sorry to hear your shakedown and potentially your tour are endangered by the shimmy, Dan. Interesting post you just sent.When it appeared I had just binned a post which suggested that, while a particular weight setting up a vibration is possible in physics, on a bike it is far more likely that a particular *distribution* of that weight is the culprit. I binned the post on the ground that I'm far away and there is nothing more irritating, when you're already under pressure, than idiots trying to teach you to suck eggs. Just as well I didn't send it! You were there already.
Good luck with finding the right distribution of your luggage.
Andre Jute
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great video Dan,
well i'm surprized to hear the bike has a shimmy i know mine is solid at any speed.
i don't carry anything like you do so it's obvious it's down to weight .
i was going to say check your headset and are your bars dead centre on the stem, but your skill in all things bikes ruled these suggestions out .Sorry buddy know idea what the problem is but one thing's for certain if it can be fixed it's in the right place.
best of luck Dan with your tour i'm sure you will have all sorted very soon.
cheers
jags.
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Video snippets here (all I could take under the circumstances, a quick and dirty job of it):
http://www.youtube.com/watch?v=dcvXis7V8YQ
http://www.youtube.com/watch?v=kaCi3CNq2Go
Andre, thanks so much for your suggestion; I do believe it is not so much the sheer weight as the distribution. I'm guessing the rear racktop load might be the culprit, but we shall have to see.
Jags, thanks also for the suggestions. Yes, headset = OK, bars and stem centered on steerer and on bike.
I keep trying to think what -- if anything -- could have changed to induce the wobble/shimmy.
Have to admit, I thought it might be a fork-loading problem, but it rode beautifully with just a front load, as I have found on other bikes with similar trail and fork blade gauge/wall thickness and low-riders.
Back out for more testing...
Best,
Dan.
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wow thats looks serious, dan did you try swapping the wheels thats if you have another set of 600.
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Dan,
I have not experienced the dreaded shimmy, but I can feel the effect of the load on top of my rear rack when off cycle camping.
I can compare this with bringing my shopping home in four panniers, often with a greater load than when camping. The load on top definitely changes the handling feel.
I think you need to try bringing the load as far forward as possible on the rear rack (reduce the tail wagging effect) or change the load to be bigger or smaller than that which is inducing the shimmy.
I hope this helps.
Julian.
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Okay...getting closer. I also attached both rear panniers and went out for another series of speed runs. This may also be known to cardiac specialists as a stress test; by this time, I found I had to really work to top 20mph/32kph.
The rear bags added 24.66lb/11.19kg, for an on-bike total of 71.07lb/32.24kg. The only thing missing is the rack-top load at 11.02lb/5.0kg.
Everything went fine, with no sign of shimmy as fast as I could go, no-handed, one-handed, and in all positions.
However, at stop, with the *rear* brake locked, I could (for the first time in these at-home trials) simulate the shimmy by rapidly jerking the handlebars back and forth while straddling but not restraining the frame with both feet on the ground. I'm also a step closer to describing the effect and why it manifests in the middle of the top tube. The masses at either end are joined by a (relatively) flexible member. When this thing shimmys, the poor top tube (and to a certain extent, the downtube), serves as a linear spring actuated by and reacting to the two opposing masses at either end.
I agree with you, Julian, and Andre is onto something as well -- it isn't the mass alone that is the culprit, but the distribution. I readily agree -- if I can move the weight at either end toward the center, it is bound to help. I must be fairly fit or this number of intervals would have already killed me, but I'm good for as many more as it takes if it solves the problem so I can tour.did you try swapping the wheels thats if you have another set
No luck there, jags. The front wheel from the tandem matches, but the rear is spaced too wide to install on Sherpa. Good idea, though.
. . .
After resting a bit, I went out for more intervals. I left the front and middle loaded as before, and removed both rear panniers. I then added the rack-top load at 11.02lb/5.0kg. bringing the total weight on the bike to 57.43lb/26.05kg. The bike handles beautifully with no sign of shimmy at 20mph/32kph in all riding modes. So much for my theory of the rack-top load being the prime culprit. It may be a major contributor, but it had help from the other stuff.
Going to now strip the bike, load from the rear, and see what happens.
Thanks so much for the thoughts and ideas. At this point, everything may be useful, so please keep 'em coming.
Best,
Dan.
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your getting closer Dan fair play to you. but we (well me) needs to see video evidence ;)
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I wonder if the rear rack is flexing back and forth somehow. To check, maybe you could tape a piece of cardboard between a left and right support. If you welded a piece of metal like that, it would really stiffen the rack and prevent it from swaying right to left. But a taped piece of cardboard would be more like a fuse. It would just break somehow, like snap the tape or rip it off the cardboard. The cardboard brace should withstand a ride when there is no swaying, but break somehow when the swaying happens, if that is the source of the problem.
Nice puzzle, but your systematic investigation is practically certain to nail it.
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I wonder if the rear rack is flexing back and forth somehow. To check, maybe you could tape a piece of cardboard between a left and right support.
That's a good idea, Jim, a bit like they used to do in the old pulp-fiction detective novels when they'd tape a hair across a door and then check later to see if the hair was broken/the room had been entered.
Yeah, I wonder about that rack as well. It is incredibly heavy and stoutly built, but it is not triangulated side-to side like the Tubus (it only has a second crossmember at the rear, down couple-centimeters from the ones that make the load deck. The Surly front rack was too laterally flexible for me, so I sold it. The rear appears much stiffer (I even reefed on it with both hands and couldn't budge it, and the load appeared steady in that way), but of course I can't see it when all the shimmying is going on, so a "tell" as you suggest would surely do the job.
Excellent suggestion!
Boy, I wish I could get this all resolved today so I could take off on the shakedown trip tomorrow. My schedule is one factor, but the greater one is ODOT may open the Old McKenzie Highway to all traffic and if it does, I can't go (too dangerous in my estimation).
Best,
Dan.
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Yeah, I wonder about that rack as well. It is incredibly heavy and stoutly built, but it is not triangulated side-to side like the Tubus (it only has a second crossmember at the rear, down couple-centimeters from the ones that make the load deck. The Surly front rack was too laterally flexible for me, so I sold it. The rear appears much stiffer (I even reefed on it with both hands and couldn't budge it, and the load appeared steady in that way), but of course I can't see it when all the shimmying is going on, so a "tell" as you suggest would surely do the job.
I've never been too impressed with that Surly rack because of that. The Tubus Cargo is very solid, because of its triangulation IMHO. However even some flex should not give you that sort of harmonic shimmy. Before I got the Tubus I had a Topeak alloy rack for many years that was similarly straight legged, no triangulation. It was quite flexxy compared to the Tubus (similar to the Blackburn rack), but I never had speed shimmy issues.
It is probably just some sort of load distribution thing. Try different combinations, maybe load the front panniers more, less in the rackbag..... mix it about. A mate of mine had problems with a locally-made frame - speed wobbles that only showed when he was descending and only when lightly loaded with one front bag on the rear, in a crosswind. It happened several times to him, but not when fully loaded. He was disturbed enough that he bought a Sherpa frame for the bike and swapped all the parts, and now much happier.
Actually he will be cycling McKenzie Pass in the next few months, on a tour of the NW of USA on his Bike Friday :)
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Easy fix Dan. Buy a Nomad! The fates are saying you should! ;D ;D
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I would suspect the rack top bag also. I've had a few bikes to this to me, (both thorns, though not sure its anything to do with that) and in the end, was pretty sure it was the bag.
A few other factors came into play,
a) how quickly I got up to speed & the wind - almost like if not sufficient drag on the pack, then it could start me shimmying
b) how loaded the bike was, by which i mean, did the road drop real quick, unloading the tyres ? (Linked to how quickly i got up to speed)
c) Could I get thru the wobble-zone ? Always felt like I could, but in the end never had nerve to try.
I used to apply r.brake lightly if/when it happened to keep me just under shimmy speed.
Both bikes behaved fine on nigh on all occasions subsequently.
hope you get it sorted and get back to enjoying the descents
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Hi All!
Back with an update after a lockout by my ISP that left the Thorn domain inaccessible to subscribers here in the States. Here's the latest on the shimmy, and it is very hopeful...
More testing
In two days, I made over sixty 25-mph runs up and down in front of the house, checking every possible load permutation and arrangement. It didn't help that a steady rain began to fall shortly after I started but I kept at it, getting so tired I nodded-off during dinner.
I had a strong hunch the problem was likely to be the rack-top load, but I decided to let the testing remain neutral, stay with scientific method, and see what the data said.
First, I stripped the bike and added weight starting from the front (detailed in my last post) , figuring excessive front weight might be a trigger. Loaded only at the front, with front panniers, HB bag, the two 2-liter bottles at the steerer and the three 3-liter bottles on the frame, all was wonderful. Adding only a rack-top load added (11lb/5kg) /or/ the two rear panniers (25lb/11.3kg) was fine; things went sour when both were added at once.
Then, I stripped the bike once again and started adding loads from the rear. With either a rack-top-load or rear panniers, all was fine. With both, the bike felt really unstable, and rocking the front end at rest pointed up the instability. I kept adding weight going forward, and things got better in some ways and worse in others. The overall stability was far better with ballast in front, but the top tube soon developed a sine wave and little changes moved the shimmy up or down in speed. The rear load appeared completely stable on examination.
Results? -- hopefully!
Persistence pays. The more I tried, the worse things got. Looking closely, the most likely culprit seems to be the Surly Nice Rack (Rear) (Pete wins the prize for this one!). It grew much more wobbly and weak as the tests progressed, and now it can be shifted 1cm with gentle lateral finger pressure against the rear struts. Looking closely, it is an untriangulated, 3-sided box. This design gave me problems when I bought a Surly Nice Rack (Front) for the Miyata 1000LT that preceded Sherpa, and I ended up selling the rack -- unused -- on eBay. The Surly racks are made-for-stout, are really heavy, and have tremendous strength under vertical loads. Unfortunately, without triangulation, they have little resistance against lateral movement. What really tips the scales is the mounting hardware. It is wide front-to-back and vertically, but narrow side-to-side. Despite all the heavy tubing, the mounting points come down to squashed tubes about the thickness of a washer. Those mounting points are also stainless-steel, which work-hardens pretty quickly. I wouldn't be surprised to find some micro-cracks when I remove it. In contrast, the triangulated Thorn Low-loader Mark V front pannier racks are no problem.
A Solution? Maybe!
I have sent for a new Tubus Cargo Evo rack. It is a new design for 2012, and represents an evolutionary development of the world-tourist's standard, the Cargo. The top deck has a closed "Return" at the front, and has a narrower load deck to aid in triangulation. It has die-stamped, 3-D mounts at the dropouts, and looks to be a structurally sound design. Though it weighs only half what the Surly weighs, it is rated to carry 8lbs more. The price really hurt at USD$140, but if it solves the problem, it would be cheap at twice that, as it would set everything right.
It is on the REI truck being driven down from Seattle, and should be in to the store for me to pickup today. I'll install it sharpish and take it out for more test runs. I must have pretty good cardiac health or I'd be dead from all the interval training. In car-centric 'Merka, the neighbors have me pegged for a nutter so I've nothing to lose on that score.
I so hope the present rack is the culprit and the new one will solve the shimmy problem. As an (amateur) frame designer and builder, I know the precipitating factors in the usual shimmy -- various influences of weight and weight distribution, coupled with gyroscopic precession of the front wheel secondary to trail and over-damping of same -- but this was different. The real clue (if I had been smart enough to see it earlier) was the entire shimmy could be simulated with the fully-loaded bike at rest. Simply by rapidly turning the handlebars, a sine wave could be introduced through the top tube. It was made far worse when the rear brake only was locked, providing a pivot point and axis for the wobble at rest; my weight did the same while riding. The test data indicate this is a classic case of "the tail wagging the dog"...in this case, precipitated by a wobbly rear rack.
Updates to follow when the new rack is installed, loaded, and testing is complete.
Best,
Dan.
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great to have you back Dan, hopefull the new rack will solve the shimmi problem.
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A bit sad to pass this on after your purchase, but you do know about The Touring Store (http://www.thetouringstore.com/TUBUS/Cargo%20evo/CARGO%20EVO%20PAGE.htm) ? Waynes prices are quite competitive.
Hopefully the new rack should be a lot better for you anyhow.
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A bit sad to pass this on after your purchase...
Not to worry, Pete, and I appreciate the suggestion. Yes, Wayne's prices are very good, and I have dealt with him before and found him very good. In this case, I tried my best to weigh my options. USD$120 or $140 is a lot of money to me, and I cannot tell if the new rack will a) fit and give the clearances I need or b) will solve the problem.
Wayne is really good about returns, but very understandably, he needs items returned in the same unused condition as when they arrive. Often, when I have a question, seeing the product in person or measuring it carefully for clearance or just holding it up is enough to answer any remaining questions without installing it, but in this case, I will have to at least carefully mount the rack and then (after wrapping it with tape) mount the bags to see if it is stable under load and addresses my shimmy problem. There is a risk and possibility the mounting hardware could show slight marks, and then it wouldn't be returnable to Wayne.
I don't return things frivolously to REI, but I figured in this case, it would be worth the extra $20 (free shipping if it is sent direct to the store for me to pick-up) to answer all questions. I fully expect this to solve the problem and I can't imagine returning it, but...well, I guess you could say it is peace of mind "just in case" the unlikely happens and it doesn't work. One thing that concerns me a bit is Tubus' cautions about tire and fender clearance. Of course, I can only see their measurements in plan view, but they say the rack limits tires to 50mm and fenders to 55mm. I have both. I also have a lot of (needed) clearance between fenders and tire, so I don't know if that will push me into an interference fit or not (the triangulated rear brace is formed into a narrowing, inverted "U" and could potentially strike the fender edges depending on how high the fender rides compared to the rack dropout mounts). If it goes wrong, I can return it to REI for free in person. If it went wrong and I had to return it to Wayne, it would cost me about $20 in return shipping, making the price difference a wash.
At this point, I'm just biting my nails hoping the new rack does the job. It should have arrived at the store yesterday or the day before, but REI's policy is to co-load their trucks with local merchants to reduce overall carbon footprint, so the trucks often take a "milk-run" on the way down from Seattle. Also, it is the weekend, and local store staff may not yet have had time to scan the arrivals, bring them upstairs, and then store them on the rack system before notifying me with an email for pickup. The official "due date" is Tuesday, but I'm really hopeful for arrival soonest so I can lay my concerns to rest.
Good suggestion, though, and most welcome; thanks!
All the best,
Dan.
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I get some shimmy on my Sherpa when I have panniers on (front and back). It starts at 20mph and eases off again around 25mph, it's not severe and dampens out with a knee against the top tube. Seems to vary depending on the load in my front panniers which are fairly big (older style Altura Orkney model) and probably sometimes a bit overloaded as the right hand one is my food pannier.
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Hi All!
Next chapter...
What's this?!?
The Tubus Cargo Evo rack arrived at REI today, and after mounting, it didn't look right. I discovered in fine print on the packaging...they had mis-filled my order at the warehouse! :o The rack I received is the one intended to fit even a "29er", a bike running really fat MTB tires on 700C rims and/or 26" bikes, the latter leaving an awful lot of clearance above the rear fender. It is ridiculously tall on Sherpa with fenders and 26x2.0 Duremes, and because of the height, I cannot fit the previous load atop the rack because it won't clear the Ortlieb underseat tool bag. Despite the published specs saying there is a 13mm/.5in difference in height, the sticker on the hardware package with this rack claims a "+2cm" designation, more than .75in. The lower model would still clear the rear fender by quite a lot...and I'm running pretty generous fender clearances.
Since the rack is now mounted to the bike, I will go ahead and test-ride it and see if it fixes the handling problem. I have placed a new order for yet another of the proper size, it will arrive in a week (another week! More delay...), and hopefully the order will be filled correctly and all will be well.
Observations; "Evo" does indeed mean "developed further"
Meantime, I have some observations about the new-for-2012 Tubus Cargo Evo in my possession...
1) It is not made in Germany or the Eurozone, but in Taiwan, according to the plastic bag that contained it.
2) The little plastic tube end plugs...all mine were missing but one. They're poor-quality plastic and a little undersized. They must have fallen out in handling at some point before ever reaching me.
3) Unlike earlier Tubii, this model is not brazed, but TiG-welded. I think this may be a good thing. It always concerned me the brazed side joints on early Tubus racks weren't coped or mitered in any way. By welding, the steel is actually melted together. Sure doesn't look as neat, however.
4) The finish is incredibly fragile, at least compared to the Surly. One single fitting of the pannier hooks left permanent marks. If it matters to someone, the finish is well toward the glossy side of satin, rather than matte.
5) The tube diameters are the same as the Surly at 10mm, but the 11mm Ortlieb hook adapters rattle noticeably compared to the Surly. Leaves a lot of room for anti-scratch wrapping. No protective "foil" tapes were included as in the past. This point is made in the instructions.
6) The mounting instructions on Tubus' website are labeled a "Preliminary Version!". And is! Even the instructions that arrived with the rack shows fastener types that do not match what came in the package, and the designations are "off".
7) Unlike their earlier racks, Tubus chose to use Torx bolts to hold the mounting rods and hardware at the front of the rack. Though the instructions designate them as T25, they are really T20...an odd size not many cyclists would already carry. The remainder of the mounting bolts are stainless allen bolts (though the instructions designate all-Torx). The Nylock-style nuts weren't very grippy; I'll use Loctite if I keep the rack. I'll also probably substitute stainless hex-head bolts for their ease of use and greater head-torque rating.
8 ) The stainless steel mounting hardware was really crudely machined with lots of tool marks and no cleanup. I found this out when I slid one eyebolt over the black-anodized forward mounting strut...and left behind a trail of silver scratches through the anodizing. I had to go to work on the second one with my jeweler's and riffler files to get it to fit at all.
9) Tubus' new "3-D" lower mounting bracket is not stamped as has been reported on the 'Net. Instead, it appears to be an investment casting. The mounting hole would accept a 6mm bolt. Unfortunately, the well for the bolt precludes use of a hex-head bolt (no socket wall clearance), and there is no room for a flat washer beneath the bolt head. Some small-diameter washers were included in the mounting kit, but remained unaddressed in the instructions. I'll bet I know what they're for. [EDIT: Yep; the small washers can be stacked under the lower 5mm allenhead bolt to adjust the effective length of the bolt so it doesn't foul top-gear on the cassette].
10) Unlike the earlier flat, stamped-steel lower mounting plate, the 3-D mounts do not include a mounting eyelet for fender stays. Unfortunately, the rear rack struts come almost exactly over my upper fender stays for the rear fender, causing interference with the rack and pannier hooks as well as noise (the fender stays rattle against the rack struts). Tubus offer a small stainless steel bracket that attaches between the rack's taillight bracket and the rear fender, obviating the need for the upper fender stays. Yes, I will need that accessory bracket. I'm guessing most Thorn owners running SKS 55mm fenders and this Tubus rack would need the bracket also.
The Surly Nice Rack (Rear) has to be the problem
Before fitting the Tubus Cargo Evo rack today, I removed the Surly Nice Rack (Rear). This just has to be the source or at least a major cause of the wobbles. Not only is the rack an untriangulated 3-sided box with squashed-tube mounting brackets with the narrow dimension inline with the frame and offering no resistance to lateral movement...the front two mounting stays cannot be made to stay tight. I know they were tight to spec when I installed the rack, and I used blue Loctite to secure the grub screws. Off the bike, these forward mounting stays are so loose they wobble 5mm each way when I shake the rack. Worse, they don't stay tight. It appears there is not enough captured area in the radius of the mounting spacers to prevent the brackets from moving sideways. Yes, they were secured to Sherpa's mounting bosses, but even so, when the rack wobbled, the stays moved as well because of their thin, narrow mounting points. This would surely (Surly?) explain the origin of the wobble and why it progressively worsened throughout my testing. It wasn't present in earlier test rides with even more weight overall.
The good news is that -- even in a size too large/tall -- the Tubus Cargo Evo is worlds more stable and I really can't move it more than a mm or so in toto with lateral hand pressure at the extreme end of the last bag-stabilizer strut, which is not itself directly load-bearing.
Uh-oh; the Rack Search continues
Trying my Ortlieb BikePacker Plus bags on the Tubus Cargo Evo did point up some differences in dimensions compared to the Surly, causing some problems; these may cause me to consider the Tubus Logo Evo instead:
The top deck on the Cargo Evo is considerably narrower than the Surly (114mm/4.5in Cargo Evo vs 160mm/6.3in). Unlike Ortlieb's Roller bags that end essentially at the top of the stiffener (plus the roll), the Packer bags have a drawstring and overcap closure, which allows them to stand well proud of the rack-top -- 11.4cm/4.5in when full. As a result, the Packers leave a valley between the two caps. If one carries a dry sack crosswise atop the rear rack (as I do; it holds my sleeping bag and pad, silk liner and air pillow), that valley has to be filled to make the dry sack stable in carry. With the Surly's wider rack, I was able to better fill the valley with my 10l MSR Dromedary water bag and a little 3/8" closed-cell foam sit-pad that also protected the rack and load from each other and the pannier hooks. The narrower top of the Cargo Evo doesn't allow for this very well. I can use the Dromedary filled with water or air as a spacer of sorts, but it is really too wide. Similarly, I can put the tent lengthwise on the rack to fill the valley, but it is too tall, making a fulcrum for the drysack to pivot on.
Logo Evo's differ'nt. Way. And maybe better for my needs
The Logo has a second set of pannier-hook mounting rails situated 58mm/2.3in below the rack-top. Although the Logo Evo's top deck is even narrower than the Cargo Evo (85mm/3.3in at the front, 99mm/3.9in at the rear in a wedge shape vs the Cargo Evo's 114mm/4.5in parallel), I think putting the bags and their extended caps lower would allow me to use the caps to effectively extend the rack-top, giving a more stable platform for my rack-top load. The panniers and everything atop them would ride 58mm/2.3in lower, lowering the center of gravity and giving needed clearance beneath the Ortlieb underseat tool bag to get the rack-top load farther forward. The downside? The panniers would have to ride exactly 12.7mm/.5in further rearward to give the same heel clearance. Sounds like a fair trade for more stability and less risk of sway/shimmy. An added benefit? The Logo Evo is rated to clear 65mm fenders and 60mm tires vs the Cargo Evo's rating of 55mm fenders and 50mm tires. It should solve the problem of fender stay-rack interference I have now.
On the downside, I expect the Logo Evo to work miserably with my rack-top pack for day rides. Maybe I can put a stiffener in the bottom of the rack-pack and tie the front to the seatpost to aid stability. The Logo Evo's platform is really too narrow to support such a bag very well. I'll have to deal with that later. Right now, the priority is to make Sherpa expedition-worthy.
So...now what?
I guess the thing to do is to send for a Logo Evo and give it a try as well. Now I know the finish can be scarred by a single mounting of the bags, I will wrap it with tape first and if it doesn't work, off to eBay it goes. It is a little sobering to think I will have USD$400 in racks charged to my card until I figure this out, but I'm getting desperate. Time is my biggest factor. I have arranged my work and appointments for this window in time, and if I have much more delay, it will affect the kind/length of trip I can take (and the four+ months' planning that went into it). Much more delay will also put me into really torrid weather, and that has serious implications for desert travel. Ground temps of 134F/57C are hard to deal with. In midsummer 2010, I ran into air temps of 125F/52C while climbing Fort Rock and it was pretty enervating. Yeah, better to send for a bunch of racks and try them in a short timeframe than miss my departure date by too much. I can always sell the unwanted the racks after I return.
Making the best of the meantime
Meantime, I'll try the too-big Cargo Evo that is now on the bike to see how it works. The shorter, properly-sized one has got to be even stiffer, so if I get good results with reducing or stopping the wobbles with this one, I'll know I'm on the right track.
Any more ideas on this, "the latest"?
Any thoughts or experiences from those owning a Logo Classic or Logo Evo are most welcome also; many thanks in advance. Andre, don't you own a similarly designed Cosmo? Nighttime now, but pics in tomorrow's daylight if I can manage it.
Best,
Dan.
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Any more ideas on this, "the latest"?
Any thoughts or experiences from those owning a Logo Classic or Logo Evo are most welcome also; many thanks in advance. Andre, don't you own a similarly designed Cosmo? Nighttime now, but pics in tomorrow's daylight if I can manage it.
Dan:
My experience of Tubus is essentially the same as yours, profound disappointment with their carelessness.
On the Thorn Board, because everyone is so polite and I'm a guest, at http://www.thorncycles.co.uk/forums/index.php?topic=4015.msg18057#msg18057 in the Titanium Rack thread, I was probably not outspoken enough.
But on the rec. bicycle.tech board at http://groups.google.com/group/rec.bicycles.tech/browse_thread/thread/dddd7d2fba2eea3/89e19b1ce3c7d4cf I spoke my mind clearly: "Tubus Cosmo Rack = Expensive Crap for Posers".
I also published first impressions at http://www.freag.net/en/t/1iu8f/tubus_cosmo that were marginally more positive.
My conclusion is the same as yours. The main thing that Tubus gets right is that, once you've provided your own mounting hardware, the rack is rock solid.
In any event, the Cosmo is, in my opinion, a mickey mouse rack, probably marginal even for credit card touring, definitely too small for your sort of touring. I'm amazed to discover you're considering even narrower racks than the Cosmo. The usable (from where a tall load would butt up against the saddle) top surface on the Cosmo is 120mm wide by about 290mm long on my Kranich on which the extra-cost extension mounting kit is used to raise the rack above the huge 60x622 Big Apples and SKS P65 fenders. On a 26in bike you may be able to use the same extra fitting kit to move the rack rearwards for necessary heel clearance for the panniers, which is in fact its intended purpose according to the fellow at Tubus, and then you get a load surface of about 120x310mm. (These measurements, compared to what you give for the other Tubus racks, make the Cosmo sound positively desirable by comparison! I really wish a proper German maker, say Humpert who now owns SL, would make a stainless rack, perhaps on the superb old SL pattern.)
I've kept the Cosmo because it is rock solid (once you bring your own bolts, nylock nuts or Loctite, and pay extra for the fitting kit), doesn't rust, and its permanent shortcomings don't really matter in my kind of use: all I hang on it is an open-top pannier basket that rarely gets taken off the bike so that the angled lower rail is only an intermittent rather than a daily irritation, and all that stands on it is my leather saddlebag, which doesn't need the support because it has a stiff bottom.
If you want measurements of Tubus bits, just shout, Dan.
The problem with obtaining a better rack than Tubus makes -- Madison for instance -- is finding a supplier who has one in stock for immediate delivery. (The only alternative stainless steel rack to the Cosmo is probably out of production.)
Andre Jute
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sorry your having so much trouble Dan,
i have the classic logo and have to say i have had no problems what so ever.
but i dont carry as much as you .
but anyway so far its held up pretty well.
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Hi Andre, jags; thanks so much for your ideas and input. Very much appreciated!
My conclusion is the same as yours. The main thing that Tubus gets right is that, once you've provided your own mounting hardware, the rack is rock solid.
Absolutely right, Andre. I have found over time that a manufacturer's reputation gets them in the door for my consideration, and user reviews help them along the way toward my purchase. However, it is their actual performance after the sale in meeting my unique requirements that really earns them the gold star...or not.
The one thing Tubus really has going for them is their triangulated steel-tube rack design. Their build quality is in general a bit pragmatic with regards to finish; indifferent when it comes to fasteners and hardware. At this point, caught in my kafkaesque nightmare of trying to get the bike working right again, I really don't care so much about finish and OEM hardware. If it'll work by throwing new nuts and bolts at it, I'm good. It's not lowered standards on my part, but the desperation of a time crunch mixed with pragmatism. I can polish bolt heads or repaint the rack after I return. Right now, it just has to work. Elsewhere...I spoke my mind clearly [elsewhere, wrt the shortcomings of the Cosmo]...
...passionately and eloquently as usual; glad I read it. I've kept the Cosmo because it is rock solid (once you bring your own bolts, nylock nuts or Loctite
Just what I am hoping for and intend doing! I'm amazed to discover you're considering even narrower racks than the Cosmo.
So am I, Andre; astonished! It seems counter-intuitive, but the idea in doing so was several-fold:
1) Drop the cap-top Ortlieb packers to near-rack level, thus extending the effective rack top and increasing stability for loads carried crosswise.
2) Dropping the bags drops the cap-tops and all that rides on them, allowing me to push the rack-top load as far forward as possible, right under the rear of the saddle and close to the center of the wheelbase. This just has to help with the wobbles.
3) Narrowing the top deck of the rack effectively triangulates the entire rack, not just the last strut (the front struts cant inward only mildly on the Cargo).
4) The newer, Evo-series racks come with the cast lower mounting plate which in my tests really does increase lateral rigidity. I really want the Evo mount in a plain cro-mo, heavy-touring rack, and at present that limits my choices to the Cargo Evo and the Logo Evo. On a 26in bike you may be able to use the same extra fitting kit to move the rack rearwards for necessary heel clearance for the panniers
An excellent suggestion, Andre, and one I will surely keep in mind. If possible, I would like to try other means first, as I want to carry that mass as far forward as possible. Taking careful measurements, I think I can get where I need with adequate heel clearance by moving the bags rearward only 13mm/.5in. Not a bad tradeoff if I can get my bags and rack-top load lower and also move the rack-top load forward.
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As an aside...
I'd never consider trying to convert an Ortlieb RollerUser, but I love my drawstring-closed, cap-top Ortlieb Packers. I use the caps as extra pockets to carry things I need quickly and don't want to dig in the panniers for. My LF top-cap carries my wool cycling jersey with nylon wind panels. My RF pannier top-cap carries my fleece jacket. My LR pannier top-cap holds all my rain gear in a stuff sack. My RR pannier top-cap holds my off-bike Merrell Breeze II nylon mesh clogs and my chair. This way, I can peel off or add jackets or rain gear, switch shoes and even have a seat while doing so...all without having to remove stuff from atop my rear rack or digging into the bags...just unsnap two plastic buckles,flip the lid, remove the stuff sack with whatever, and put it on...or take it off. I'm addicted to the sheer convenience of it all.
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That's my reasoning, anyway. If the Logo Evo doesn't work, the 26" version of the Cargo Evo is on the way. I ordered the Logo Evo and a mudguard bracket for it (also fits the Cargo Evo) so I won't have to deal with the interfering top stays on the rear mudguard. I decided time is the most important factor, so I went with the FedEx 2nd Day shipping option on this latest rack. It comes from Arizona, so this will help a bit in getting it dispatched, usually the largest delay.
If you want measurements of Tubus bits, just shout, Dan.
Thank you, Andre! A very kind offer, much appreciated by me.
Now, jags...sorry your having so much trouble Dan. i have the classic logo and have to say i have had no problems what so ever. but i dont carry as much as you. but anyway so far its held up pretty well.
Oh! This is welcome news, jags! I am heartened to find they worked well for you in daily use, anyway, even if the loads we carry are different. I've seen your Sherpa but hadn't registered you had the Logo. It certainly made for a nice, clean, well-balanced load in your tour photos. Very good to know.
Thanks, gentlemen; all very helpful to me and greatly appreciated.
All the best,
Dan.
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i have the classic logo...
Got it, jags. Looks really good on your Sherpa at: http://www.thorncycles.co.uk/forums/index.php?topic=1744.0
Gives me a preview of how it might look on mine.
Best,
Dan.
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Dan if i could afford the postage i would sent it to you,
dont think i'll be using it for a while . ;)
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Just for the sake of completeness, I also published first impressions of the Tubus Cosmo at http://www.freag.net/en/t/1iu8f/tubus_cosmo that were marginally more positive than my mature reflection and evaluation. You can save them for when you return, Dan; there's nothing immediately helpful in there except that hardware store pre-drilled three-hole flat bracing/repair brackets turned out to have the holes in the right place to stand in for the Tubus fitting/raising/distancing kit while it was en route. -- Andre Jute
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I get some shimmy on my Sherpa when I have panniers on...
Hi Rual,
I've been meaning to ask you for more details on your Sherpa's shimmy. Please, could you tell me what racks you're using front and rear, and about how much weight is in the panniers and atop the rear rack? It sounds as if the problem is weight-dependent for you, and possibly more due to how the weight is distributed. Your shimmy doesn't sound as severe as mine if it can be damped with a knee; mine was unaffected when I "kneed" it. Can you tell me what size Sherpa you have?
I still think it must've been the rack, as it got progressively worse, where it was non-existent to start with when carrying even more weight.
I had to be out of town all day yesterday, so had to postpone the test runs. I try to keep the proper perspective on life, but the non-cycling world intrudes on occasion. ;)
I've got my jersey and shorts on as I type this, and should know more about how the (too big) Cargo Evo does just a few minutes from now. The Logo Evo is on-track for getting here by 2nd-day shipment from Arizona (in Oakland, California at the moment) and should arrive before 16:30 tomorrow. The proper-sized (13mm shorter) Cargo Evo is due on or before Tuesday.
Whew. With three Tubus racks at my disposal, I should be able to get some good comparative data. I've got a 16x23 matrix all set up to take the data as I get it, but hopefully I'll find myself saying, "Feels better!" or "Solved!" after just a few tries.
Thanks for weighing in with a really important data point, Rual. You're the only other Sherpa owner I've heard from who has experienced shimmy, so I'm eager to learn more.
All the best,
Dan.
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Hi All!
Thanks to my testing there's some new ruts in the pavement; unfortunately the results are nearly the same.
1) Sherpa does wonderfully with my front load (L/R panniers, HB bag) alone.
2) He does wonderfully with my front load and all the water (including the two 1l bottles on the steerera nd three 1.5l bottles on the frame).
3) Add either the rack-top load (11lb/5kg) /or/ the two rear panniers 12.5lb/5.7 each,25lb/11.3kg total and he does fine.
4) Add both the rack-top load /and/ the rear panniers, and the wheels fall off the cart, so to speak. Shimmy City. At least the results can be reliably replicated and are repeatable. I repeated all the prior two days' testing and I'm beat. Fit, but beat; interval training is a great builder of stamina.
I'm puzzled, too. I can't account for this happening.
This is with the 700C-sized Tubus Cargo Evo rack. Unlike the Surly, there's no loose-fitting parts and the rack doesn't sway when I poke at it. Moves maybe 2mm with a lot of lateral pressure on the last strut. I'm building an instrumented test rig to see how much pressure is involved, but it seems to be plenty stiff by any reasonable standard.
I've added a few more cells to the matrix of test permutations:
1) Tire pressure makes a difference, but only by stiffening the sidewalls and thereby changing the amplitude and frequency of the shimmy slightly. I used differential pressures F/R to see if there might be any difference due to effective pneumatic trail (thanks, Stuart, I kept your suggestion in mind). With 63mm of trail, the geometry of the bike is spot-on for what it needs. Really, I can't see any reason for shimmy and am utterly baffled by its appearance.
2) I swapped-in the 1.5in slicks from the tandem. No real change. Didn't fit them differentially, though.
3) I swapped places between the front and rear panniers (nearly the same weight in each, I wondered if form-factor might make a difference.
4) I checked the loads in the bags, and sure enough, all the heavy stuff is low and toward the center of the bike fore-aft and left-right.
5) I tightened the compression straps on all bags.
6) On the rear packers, I loosed the built-in compression straps and widened the bags L-R so the weight could drop further down, but at the cost of sitting further from the center, laterally. This left the entire top half of each rear Packer Plus pannier empty, so the weight really is low.
7) I checked the hub cones and the quick-releases. No problem.
8 ) The tires are well-seated on the beads. There is a small wobble in the tread of the Duremes from new, but it has never been a problem.
9) I didn't just check the headset; I re-adjusted it from scratch. It is perfect and still there is a problem.
10) The bike shimmies with hands off the handlebars.
11) The bike shimmies when standing. And, when standing with no hands and the saddle nose grasped between my legs (Not a Good Idea, but worth a try).
11) Removing the Ortlieb underseat bag and moving the rack-top load forward beneath the saddle till it grazed the backs of my thighs didn't make any difference.
Bottom line: The bike just is not happy with a rear load of 36lbs/16kg arranged as it is. I guess the next thing is to dispense with the rack-top load and put the equivalent in my free weights in the rear panniers to see if it is the weight or the placement/distribution back there that is causing the problem.
I've done about as thorough a forensic job as I know, and all the problems seem to stem from the rear load, since no other combination presents any problem at all. By the way, the frame looks perfect, with no sign of cracks, fissures, or fractures anywhere. There's no creaks and such, either.
Man, I just have to be missing something, but what...? Any further suggestions are surely welcome, and I truly thank you all for your generous ideas and thoughts to date.
Logo arrives tomorrow, with its lower load-rail. The rack itself is 3mm lower than the 700C-sized Cargo Evo currently on the bike, and the load rail is 58mm lower yet, so the hooks will sit on the rack 61mm/2.4in lower than they do now. The Logo Evo also has a narrower top deck and the entire rack leans in toward the centerline, effectively triangulating it at the front and rear against lateral movement. The top deck is wedge shaped in plan view, further triangulating it against movement.
Best,
Dan.
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Dan any chance you could put up some photos of the bike fully loaded.
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Dan any chance you could put up some photos of the bike fully loaded.
Love to! The trouble is, the option to do so is no longer available to me from my "Global Moderator" account on the Forum, and I have to figure out why. I am pursuing this elsewhere, but in the meantime...I can't post piccies.
Will as soon as I can.
Best,
Dan.
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Nomad is calling....... calling......... !!
;D
Alternatively, take your rack-top load off and put it in:
(http://www.google.com.au/url?source=imglanding&ct=img&q=http://bicycletouringpro.com/blog/wp-content/uploads/2009/07/extra-wheel-bike-trailer.jpg&sa=X&ei=n9XiT9yeHKSaiAfrrbSMDw&ved=0CAoQ8wc4Eg&usg=AFQjCNH_saZCbN-F6zoKpq2WRGgAYvlzWQ)
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Nomad is calling....... calling......... !!
But I can't heeeeeaaaaaar it....! ;)
It'll have to call louuuuderrrrr!
Chuckling,
Dan.
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Dan,
My bad. You should now have the option to attach.
Sorry.
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It'll have to call louuuuderrrrr!
I can imagine these interval work-outs are exhausting, getting a heavy load up and down a hill umpteen times. But I bet you will figure out what's going on and get your Sherpa system working properly.
I think you're smart to try the abstract away the details of the load by using simple chunks of iron and then moving those around in various configurations. Is it the total weight, the height of the center of gravity, or some lack of rigidity in the system. If you have the free weights, maybe you could just take the panniers out of the picture too by strapping the weights, cord through center hole, straight to the rack, with some newspaper to protect the finish. Maybe even newspaper between each pair of disks so the free weights don't jostle around either. Our teenager has a couple 25 pound disks. Doesn't take many of those to simulate a significant load!
This is a tricky puzzle but with your systematic approach, you will get it figured out!
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Hi Dan
do you think your (unusally?!) high pedalling cadence may be a cyclical factor in all this? You could redo all your tests in a higher gear and really sleep well.
Just a thought
Ian
PS I love the wordplay in the title of this thread.
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Hi All!
Catching up...
jags: Piccies, as requested. They're not as crisp as I'd like 'cos we took them at 21:00 hours on the first day of summer and there wasn't much light for moving subjects. These photos show the whole shootin' match atop the Surly rack. That includes 6l in the MSR dromedary water bag atop the rack in this photo. The big red dry sack contains my -15C 3lb/1.36kg winter sleeping bag, my 2.16lb/.98kg pad, silk liner and air pillow, and weighs 6.15/b/ 2.78kg total. The smaller, black sack is my tent, complete with footprint and dry sack for the inner compartment, and a variety of stakes ranging from Scandium sand hogs to titanium needle stakes, weighs 3.76llb/1.70kg. Total for the sleeping system is 10lb/4.5kg. With six liters of water, the 10l MSR Dromedary sack weighs 12lb/5.46kg and allows about one refill of the 6.5l in bottles on the frame and steerer. The rear panniers are carrying 12.5lb/5.7kg apiece, so 25lb/11.3kg for the pair, and the weight in them is packed low and forward and compressed laterally with the Ortlieb's own compression straps and my added ones that also tie them to the rack.
Since these photos -- and with the switch to the Tubus Cargo Evo -- the tent now goes under the underseat tool bag. The red dry sack goes forward right against the tool bag, putting the dry sack's weight just ahead of the rear axle. The MSR Dromedary has been switched-out for two smaller bladders with the same capacity, one in the bottom of each rear pannier. All panniers are secured with compression straps that also secure the ends of the red dry sack. The dry sack and tent load as a module, held together by webbing and Fastex buckles. They're then cinched down using weblock Arno straps. Neither the panniers nor rack-top load wiggle or bounce in any discernible way.
The Tubus Logo Evo has now made it to Springfield (yes, the one creator Matt Groening has admitted he used as the inspiration for the town in The Simpsons) and should come across the bridge to me here by 16:30 this afternoon. If all goes well, it'll let me drop the bag hooks a total of 63mm lower than they are now, and lower the bag caps to nearly the same level as the rack deck, lowering the rack-top load and letting me move it further ahead. If not...well, the Cargo Evo in the proper 26" size is coming, and it'll drop the lot 13mm lower. Not a lot, but maybe enough. The Cargo Evo's deck is a lot more usably wide than the Logo, so it may be wash. We'll see. The good weather will hold through today, then we've got rain predicted through Monday that will make test runs less fun. I'll be a busy fellow today.
Pete: Alternatively, take your rack-top load off and put it in [an ExtraWheel trailer]...
Now you're tempting me, Pete! Mightily! I've had my eye on one of those since I saw one in your touring pics. What you might see as a trailer, I see as a Water Wagon, hauling all but one of my bottles and the Dromedary, full to 10l. I'm definitely keeping it in mind, but would prefer to do without a trailer of any kind if possible for the trips I take solo. For tandem camping with 4 panniers, a trailer can't be beat. The big problem for me is the concern about the trailer sinking on the dampened playa rims of dry lakes. That photo of my Miyata I posted elsewhere on the Forum ( http://www.thorncycles.co.uk/forums/index.php?action=dlattach;topic=3990.0;attach=1187 ) showing it standing on its own in Nevada's Black Rock Desert gives an idea. It just sucks the energy out of me to churn through that stuff. If an afternoon thunderstorm kicks up and it rains when I'm out there...good luck getting back out again till it dries enough to "surface". <-- Why I have to carry the extra food and water, 'cos the water on the dry lakes is all alkali-contaminated and can't be consumed. It also means sleeping in a chair, 'cos the tent and bag would be under several inches of water. Yeah, the trailer would be a help and a hindrance. Which would depend on the situation of the moment.
Stuart: You're a gem; thanks so much, great job as always!
JimK: Yes, the free-weights with and without the panniers are a great idea. Implemented and done. Though final testing will have to be with a real load, the free-weights should allow gross changes quickly enough to give me some quick indications.
Ian: Glad you like the title; it came to me as I woggled home from that first test-tour muttering those same words. Excellent thinking wrt my high cadence being a factor. Though I pride myself on being a smooth pedaler (the French term "souplesse" just sounds so much more sophisticated, but I can't pretend..."smooth pedaler" does me fine), it could be a factor. Thinking along those same lines, I revved like mad in low gears to get up to speed without trashing my knees, then dumped it into overdrive and just barely (for me) ticked over at 40rpm. No change. Oddly, I also found that on coast-down with no pedaling input, the bike would sometimes "drop into" the wobble as I decelerated without pedaling.
I don't think it's my cadence, and I now also don't think it is a classic case of shimmy, precipitated by such things as trail and gyroscopic precession of the front wheel and such. When there's a lot of weight on the back (with or without any water bottles, front panniers, or HB bag), shaking the handlebars while the bike is at rest is enough to start a sine wave through the top tube -- much worse with the back brake locked to provide a pivot point beneath the rear tire. More and more, I am thinking it is a case of either weight transfer or related to the polar moment of the loaded bike.
Oddly, this is exactly the reason and identical symptoms/behavior that caused me to retire the Miyata 1000LT and buy Sherpa. Me 'Yata did fine all through Europe and throughout the 2010 Great Basin Tour that included the extended transit of Black Rock. On my return, I overhauled the bike, found the last strut-weld on the alu rear rack had broken, replaced it with the Surly, and then the bike became unridable thereafter due to shimmy, even with just 5lb/2.3kg in a rack-pack. Cost me my planned 2011 tour of the Ruby Mountains and cross-transit of Black Rock. I never did figure what caused that nor how to address it. I don't want that to be the case with Sherpa, but there have to be some related causal factors I'm missing. If only I could see the connection. Does anything jump out that catches your collective eyes?
Thanks so much for the kind and encouraging responses; very much appreciated!
All the best,
Dan.
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looks great Dan total mystery lets hope the new rack is the answer ::)
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Hi All,
New Tubus Logo Evo arrived
The Logo finally arrived at 14:42 this afternoon. With various things intervening, I finally got to installing it around 17:30 and it was a 15-minute job to get it on the bike (I'm getting far faster with practice, and discovered a few assembly shortcuts that really helped. Ask if you want them. Having all the needed tools and driver bits assembled at the ready made it faster, too).
With some expected problems...
There were a few disappointments with the Logo Evo, largely expected. The top deck is in a different place, and so is the light mount. Thank goodness I left a little slack when I ran the taillight lead. The top deck sure is narrow. This caused a problem I had worried about: The two front stays are too close together to fasten to the outside of Sherpa's seatstay bosses using the straight stays, so I temporarily put them to the inside. I've already placed an order for 12mm cranked (offset) stays from Tubus to mount the front stays properly to the outside of the seatstay bosses. I couldn't tell how far off it would be till I saw it installed and could take accurate measurements. Right now, I think everyone with a Sherpa and a Logo Evo would need the 12mm offset stays to do the job right, or would need to bend them that far. Order fulfillment should be Tuesday for those, so it was inside or nothing for now. The Logo Evo is not as stiff laterally as the Cargo Evo by a long shot, as it lacks the inverted "U" rear strut (why did Tubus leave it off? Or why not simply add a lower rail to the Cargo Evo?). It is possible to wiggle it laterally over a range totaling 5.7mm with 5.09kg of lateral pressure on the last strut. It does set the bags lower, which lowers everything. Bound to help.
I got the mounting hooks adjusted; the Ortlieb BikePacker panniers needing to be moved rearward just .5in/1.3cm for heel clearance, not a bad tradeoff for sitting 2.5in/63mm lower overall than on the 700C-sized Cargo Evo. Having a flat "return" at the front of the rack along with the lower pannier placement allowed me to shove the tent fully beneath the underseat bag and still clear the backs of my thighs nicely by 2-3 inches. The drysack containing the sleeping bag, pad, liner and air pillow shoves right up against the back of the underseat bag, very close to centered over the rear axle. The lot is secured fore-aft and side-to side and doesn't wiggle.
My theory that dropping the panniers would effectively extend the narrow rack deck proved out. This was the most stable rack-top configuration with cap-top Ortlieb Packers of any tried to date.
No water bag, but an additional 5lb/2.27kg in free weights in each rear pannier. The whole works is shown in the accompanying photo-collage, with detail shots of the rear load since that seems to be the source of the problem. It looks pretty tidy.
And...it helped!
I took the lot out after dinner tonight and did many runs over the next two hours. For the first time, I had no frank shimmy. It came very close, but didn't actually shimmy at any speed up to 22mph/35.4kph, nor on coast-down. When I deliberately induced shimmy by alternately tugging the 'bars, it was of lower frequency and amplitude than before and self-recovered.
But why? And not enough
That's great news in itself and the first encouraging sign since the debacle began, but I still don't know why the bike is so very sensitive to rear loads. If anything, it should be the front that is problematic, and that end is solid as a house. I still cannot understand how the bike did so well initially last fall and through the winter's day-ride testing with a full-up weight of 134lb/61kg on the same surfaces and even really bad gravel, then developed the tendency to shimmy now with less weight. Same as the Miyata.
This all still leaves me unable to depart on schedule, and I've already missed my initial routing window. ODOT (Oregon Dep't of Transportation) opened Old McKenzie Highway 242 to all traffic today, and it was flooded with sightseers; no place for me on a loaded bike with narrow two-lane, blind hairpin corners and no shoulders and very limited sightlines. I know I don't relax much when I drive it, looking as I do for cyclists potentially around every corner -- and finding them in the worst places.
The big problem is I've only got four days' worth of prepacked lightweight food aboard with one days' emergency rations (if rationed), and I need more. I don't have water to refill my bottles. I can't duplicate this loading scheme with the Cargo Evo 'cos the bags sit too proud of the rack for the rack-top load to clear the underseat tool bag and it leaves the racktop load unstable.
Why's Sherpa so rear-load sensitive?
I'm more than a bit at sea on resolving this and am about out of ideas. By all I know about frame geometry, this shouldn't be a problem, and the tubing specs are dead-on for handling such a load, particularly compared to the '89 Miyata with 700C wheels and conventional tube diameters. Sherpa is textbook-spec for the job.I've never fallen on the bike nor has it fallen on it's own. Nothing appears amiss or broken, cracked, or misaligned. It rides wonderfully unladen or with a 25lb/11kg, but so do my other rando/touring bikes.
Any and all ideas are welcome. Nothing's off-limits in terms of suggestions. I suppose it is possible that in my frame size, Sherpa is just not the appropriate tool for the job. Still several online magazine tests and reviews indicate the tubing in the extra-oversize diameters (like my 560S Sherpa) have the same tubing spec as a Raven Tour.
A new line of inquiry: tires
I'm now wondering if the wobble is due to the tires. The rigid (wire bead) Duremes have always had a wandering tread cap and the reflective bands are off-center, though the bead is equidistant from the rim edge. In the early days of Kevlar-belted tires, the belts would sometimes shift, and there were even problems with the tread de-bonding from the belts. My family had a light truck once that went through whole sets of tires 'cos the belts would separate, causing a steering shimmy until they were replaced. Might it be possible these Duremes with the wandering tread caps are no problem with lighter loads, but distort just enough under extra weight to cause a shimmy? Maybe at the rear, which carries more weight? I have a pair of brand-new folding Duremes, and will swap them on tomorrow and have another go.
Best,
Dan.
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Dan,
a glimmer of light at the end of the tunnel.
Tyres, maybe worth swapping front and rear tyres over, I know mine wear differently.
Why not try an e-mail to the designer Andy Blance at Thorn? He must be able to offer some guidance.
Julian.
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well lets hope the problem is solved, the bike looks fantastic loaded up ready for war ;)
very best of luck with it Dan sure hope your tour goes smooth i'm sure it will.
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oh just seen this Dan might be of help on the tyres .
http://www.bikeforums.net/showthread.php/794790-Schwalbe-Marathon-XR-tires-various-sizes-all-new
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I just ran across this thread. I have had two bad shimmy problems during my 50 plus years of biking.
First shimmy experience. As a kid with a newspaper delivery route, I had those really huge steel wire baskets over the rear wheel on a single speed coaster brake bike. Some kids where chasing me and I was pedaling as hard as I could to try to get away from them, the baskets that were full of newspapers started swaying back and forth (resonance) and it literally launched me off of the bike.
Second shimmy experience. Long Haul Trucker, Surly racks front and rear. Very bad shimmy but I could ride it. Was much worse on pavement than on gravel, fortunately most of the trip was on gravel. After a few days I figured out that my front pannier weight center of gravity was a too far to the rear, moving the center of gravity forward to the location of the hub fixed the shimmy. Still felt a bit wobbly and flexible, but the resonance was gone.
Next tour, no shimmy problems. This was with the Surly racks on a Thorn Sherpa (610S). On this trip I found that if I stood on the pedals to try to accelerate instead of staying in the saddle, the bike felt really flexy, so I did not do this anymore. I suspected that the flexible feeling was the Surly rear rack, but can't say for sure. I decided the Surly front rack is too heavy, replaced it after this trip. This trip was on gravel with 26X2.0 Dureme on front and Extreme on rear.
During the past month I have been getting ready to go on a tour with my Thorn Sherpa, Surly rear rack and Tubus Ergo front rack. Handled great with about 11 pounds (sorry, I am in USA, I don't think in kg terms) in each front pannier and maybe 16 pounds in each rear for my test ride. Sherpa felt great with new Marathon 26X1.5 tires which I bought just for this trip. Change in tires is since this trip will be almost all on pavement so I did not want the 2.0 width tires. Decided to test the LHT with this weight distribution, it also felt great with these four panniers but decided to use the Sherpa anyway. When I added a duffel with about 16 pounds to the load on top of the Surly rear rack (in addition to the panniers), it suddenly felt much more flexy. It did not have the resonance problem that I had before with the LHT, but it still felt a bit too flexible. For this reason, started thinking about a different rear rack. Photo below was taken yesterday with the Surly rear rack and duffel on top.
I ordered a Tubus Logo EVO two days ago. If it does not arrive on time for my trip, the Surly rack will work for me, as I did not get a resonating shimmy. But, I hope the new rack gets here in time. I hope I have better luck than you for mounting brackets.
I concur with your opinions on the lack of triangulation stays in the Surly rear rack. That concerned me when I first opened the box it came in several years ago, it reminded me too much of the system I had used as a kid to carry newspapers. But I used the Surly rack anyway. I went with the Logo instead of the Cargo specifically because I wanted to have the lower pannier position and because when I looked at the drawing of the Logo from the rear, it just looked so sturdy.
http://www.tubus.com/documents/1323435489_LogoEvo_BM.pdf
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Hi Dan
if you scroll down to the bottom of this page http://cyclotouriste.co.uk/index.htm you'll find reference to an article describing testing for shimmy. But possibly you know more than the author by now.
Ian
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This also looks like a great set up,
but can i just ask have you guys concidered loosing half the load :)
i'm not being a smart ass but what on earth have you got in all those panniers.
surly for a two or three week tour you could fit everything into 4 panniers.
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Hi All!
Some exciting additions to this thread, and it is frustrating that due to the press of daily life, I have defer my replies till later today. I'll jump on this one, though, 'cos it's core to the discussion...can i just ask have you guys concidered loosing half the load. i'm not being a smart ass but what on earth have you got in all those panniers. surly for a two or three week tour you could fit everything into 4 panniers.
No, you're not being smart, jags, it is a logical question to ask and I'm glad you did. I've detailed my load elsewhere on the forum with pics, but basically...
1) My two front panniers carry nearly all my "stuff" Why? Because the contents are small and dense and stable and unlikely to change in volume much and I can take either of the two small bags into the tent with me or reach down and filch stuff out of them while astride the bike when stopped:
- Stove
- two alu bowls I use as pots
- 1-liter of stove fuel (white gas or unleaded gasoline as the case may be).
- small toilet kit.
- reserve tools and spares
- spare folding tire, 2 tubes, 2 patch kits
- small paperback novel
- small plastic box with rechargeable batteries
- 1 pr. riding shorts
- 1 pr. casual shorts
- 1 spare jersey
- 2 spare socks
- lightweight fleece jacket
- lightweight long-sleeve wool jersey with nylon wind panels on the front.
- lightweight wool tights
- lycra tights
2) The HB bag carries:
- Some energy bars/snacks in double zip-lock bags to reduce "bear smell" and are eaten away from the HB bag.
- A little sack with my lightweight wind jacket
- A little sack with my sun hat, my light fleece balaclava, and my billed hat
- my wallet and lock keys, spare camera battery.
- my slim little flash-video camera (digital camera goes in my rear jersey pocket)
- "dumb" 3G CDMA cell phone with great battery life and tower reach. Even so, often out of reach for days.
- small sack for prescription meds for thyroid and pollen allergies, toothbrush and paste, floss, and small tube deodorant.
- small notebook and pen, small first aid kit, all-purpose pocket pack of paper tissues.
- small silicone cup, used primarily for snagging water from restroom faucets that are too shallow to refill my water bottles.
- small plastic zip-lock bag with bug spray, sunscreen, lip balm, zinc oxide, another Kleenex packet and two flat dust masks for dust storms.
- Map goes in case on top. LED headlight goes in side pocket with another little bottle of eye drops. Other pocket has two little packs of tissues (serve as napkin, snot rag, and toilet paper in descending order of multi-use).
3) Rack-top drysack carries:
- 3lb/1.36kg winter-weight down sleeping bag good to -15C; use as a quilt in warm weather.
- 4.6oz/.13kg silk liner; use alone as sleeping bag on blistering hot, 80F/27C nights.
- 2.6oz/70g air pillow
- 2.21lb/1kg winter-weight dual-chamber sleeping pad
- 9.2oz/260g sleeping bag stuff sack and lightweight, 35l dry sack
4) Other rack-top sack contains:
- Tent at 3.75lb/1.7kg with fly and footprint and a variety of stakes including deadman flukes for snow and sand and titanium needle stakes for rocky soil
5) The rear panniers contain what I call the Cycle of Life: Food and water in, waste um, "out":
- Two side pockets: small pocket packs of paper tissues, whose shape and size makes them more ideal than rolls of toilet paper.
- Toilet trowel & Steripen UV water purifier and filter plus some pills for if the batteries go dead
- Small roll, bin liners for trash disposal.
- GoPro vidcam and chest harness/helmet mount (18oz/510g).
- Under 1 bag cap-lid: My rain gear (helmet cover, gloves, booties, jacket, pants) @ 2lb/1kg.
- Under other bag cap-lid: Camp shoes (20oz/570g), folding Alite Monarch chair (20oz)
- Food. Varies, depending on whether I am near stores or have to carry a week's supply. At home, I repackage the food to minimum dimensions and go with a lot of dry stuff and food in foil pouches. At the little rural stores I find on my route, most stuff is either canned or microwavable. MW stuff can do, but does not turn out well. So, it is usually cans. Because the bulk and type of food vary so much, it all goes in the rear panniers, which can be expanded or compressed to hold it. It also means there is no food smell in any other bags, so all I have to hoist into a tree at night is the two rear panniers. Bears aren't a problem in the desert, but they surely are in the heavily forested mountains I cross on the way there and back.
- And, of course, the rear bags (Ortlieb BikePacker Plus) weigh something. So do the nylon webbing straps I use to secure the lot. By the way, Arno straps rule.
Besides food, the big weight for me on my extended, self-supported, solo desert crossings is the water. When all bottles are full, I carry 1.7 US gal/14lb (6.5l/6.5kg) on the frame.
I also have to carry extra water for when I'm spending extended time where water supplies have been poisoned by alkali and cannot be made potable (I carry pH strips to test first). To cover that contingency, I have a 10l MSR Dromedary water bag. If I carry 6.5l in it, that allows me to refill all the bike bottles once. This can be on the knife-edge of needed capacity. All the water is for drinking and cooking only. I cook in freezer bags so there are no dishes or pots to clean (the used sacks become trash bags for responsible disposal later). I don't bathe for a week or two at a time (Eww, but true) except for the occasional wipe-down of um, "delicate" areas. I wear really lightweight undershorts that can be rinsed under a water bottle stream and air-dry in a few minutes in the low humidity. The shorts and their synthetic chamois get washed about once a week, and sometimes ride wrongside-out atop the racktop load so the sun can do its work on them. Waterless alcohol-gel hand sanitizer and gel deodorant keep-down bacterial growth in the nether regions. There's many other tricks and tips I've developed over the years that help, often coming from military training practices.
This seems to be the irreducible minimum for what I do, leaving a minimum margin for safety and durability.
I've got to deal with temperature extremes -- hot and cold. June temps are often 9F/-13C at night in snow when crossing the mountains from the Valley to the Central Plateau and then desert regions. Last trip through, the rangers closed the gates at Steens Mountain due to whiteout conditions near the summit where I'd planned to overnight. Once in the desert, nighttime temps of 18F/-8C are common, and my bottle freeze solid if I don't bring them into the tent and place them on the foam sit-pad. During the day, air temps are commonly 124F/51C. My temperature data logger has repeatedly recorded well over 148F/64C on asphalt, which melts and sticks to the tires. This is why I need the chair to keep me up off the pavement with an air-gap when I stop; the foam sit-pad tends to stick to the melting tar, and if I sit on the pavement directly, I get scalded and the tar sticks to me like napalm. There's no shade. I've though about packing a small umbrella and expoxying a 10-24 nut to it for my camera clamp to fix to my rear rack at stops in my chair, but the wind would blow it wrongside-out. I used to just stand around when I stopped for a brief rest, but I may be getting um, "more experienced" (*not* "older"). That's why the chair now holds more appeal.
I am just warm enough if I wear everything I've got when it is coldest (3-5F/-15C--16C) and I'm standing still:
- Jersey, shorts, socks.
- spare jersey, shorts, socks on hands
- all the rain gear
- hats/balaclava/helmet cover
- lightweight fleece jacket
- light wool long-sleeve jersey with wind panels
- tights, wool and lycra
When I'm working (riding), then the layers come off. They go back on when I stop, hence the convenience of storing the two jackets and rain gear under the bag-caps where I can get them by just unsnapping the two buckles and flipping the lid. Really helps to leave the main bags closed if it is snowing, pouring rain, or in a dust-storm.
I almost always toss in a couple pairs of women's pantyhose (tights) as well. They are light, cheap, and provide a couple more layers' warmth for minimum bulk and weight. I've sometimes cut off the legs and used them as long sleeves to reduce sun exposure (lighter than bigger bottles of sunscreen). They also make it harder for ticks to bite and attach themselves and work great as silt and scum filters for skimming water from cattle troughs before hitting it with the SteriPen and/or pills. I recommend them highly if you can get over the idea of it.
The tent is a 1-person jobbie; I only stay in it to sleep. If it rains, I ride in the rain and cook in the rain; the tent is just for sleeping. The rest of the time, I am on the bike 16-17 hours/day and usually eat on the bike. The one cooked meal of the day is dinner in camp before I crawl into the tent to sleep.
I've got to deal with winds. When I break camp I try to get in at least 20mi/32km before eating so I can make some distance before the winds start. Afternoon winds are usually steady, blowing the alkali dust at about 39mph/63kph. They're usually quartering or headwinds, but occasionally I'll pick up an oikaze (favorable following wind, as Japanese fishermen call it).
For off-bike recreation, I take landscape and flower photos and soon video and limit myself to reading a chapter a night to make the one paperback novel I take last as long as possible. I also listen to the little 1-AAA battery-powered AM/FM/Weather radio I carry or my little .8oz/22g rechargeable MP3 player (America's "A Horse with No Name" usually seems appropriate).
So, that's what I carry, and where. About the only weight I can lose or vary is the amount of food and water I carry, and there's times I need all of that I can lug.
All the best,
Dan.
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I will keep this short. Yes I have considered trying to cut weight.
Several years ago I decided after a canoe trip that my pack was too heavy. So, I weighed all of my camping gear, item by item. I then put all the data into a spreadsheet. From that I could compare weights while deciding what to bring - do I bring this stove at 17 oz (again, sorry not using SI units, am in USA) or this other stove at 21 oz? Etc. I have expanded that spreadsheet with biking gear, kayaking gear, backpacking gear, etc.
Right now my gear is about as light as it can get. I will however start out with 4 days worth of food since I do not expect to see a store for 4 days. Trip is 2 weeks, but realistically you bring the same gear for a week or for a month or two. Weather, I expect 30s to 90s (Farenheit) or roughly freezing up to mid 30s C, which complicates clothing and sleeping bag options. Over the past month and into the foreseeable future, it has rained more days than it has not where I am going, thus the waterproof gear.
The duffel will be roughly half full most of the time, but it will have room for extra water bottles and food. I have a piece of cardboard rolled over the bottom half inside the duffel to keep it straight and not sagging, but with the new rack I may put the duffel side to side instead. When I took the photo, I had four liters worth of empty water bottles in the duffel to help fill it up.
Assuming the two front panniers are 25 liter, the rear are 40 and the duffel if it is only half full would actually only have 15 liters in it, I am pretty close to only using four panniers.
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ok lads point taken ,i'm only a fair weather tourer if that. :-[
but saying that we are all kinda spoiled these days with all this light weight gear on offer.
and all the high tech cloths/ panniers /bikes and what not.
how did the cyclist do years ago when this gear wasn't available.
i often seen lads on old steel bikes with one or two bags touring the world how the hell did these guys do it, makes you wonder.
i'm not saying you won't use all that gear maybe you will maybe you won't. but if wasn't there you would never look for it.
yip we are all home creatures at heart ,guess if that 36inch flat screen tv only weighed a few grams , it would have to come along.
just winding you guys up ;D ;D ;D
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Hi Mickeg,
I am so glad you have joined this thread, as our experiences with Sherpa handling and racks appear similar.
As you have already read to this point, the battle continues to find and address the root cause of my shimmy.
The next phase of my investigation will take place after the Tubus Logo Evo struts arrive by FedEx on Tuesday. Since that is the first rack combo that has (barely) stopped the shimmy, it seems a good baseline on which to build. Of particular note for you and your efforts, the Tubus Cargo Evo proved more rigid and resistant to lateral movement than the Logo Evo, but the lower mounting rails and flat "return" (loop) at the front of the Logo Evo seemed to help more, due to variations in weight distribution (panniers lower, rack-top load further forward). The one thing I really don't like about the Logo Evo? The top is so narrow it doesn't do a good job supporting my rack pack on day rides; a real disappointment there. It is more like a Tubus Fly with lowered side rails than a Cargo or Cargo Evo. On the other hand, with my cap-top (non-roller) Ortlieb BikePacker Plus rear bags, the extended caps and the narrow racktop are all in the same plane and I get much better support for the rack-top drysack and tent sitting crosswise.
Right now, I have the Surly Nice Rack (Rear), the 700C/28"/26" Tubus Cargo Evo, and the 700C/28"/26" (only available in one universal size) Logo Evo. A 26" Cargo Evo is in-transit (rack top is 13mm lower) and the offset forward struts for the Logo Evo. That's a lot to play with as I continue testing.
I hope your new Logo Evo will work well for you, and bring the results you seek. Certainly, your bike is stunning in appearance and just looks so very nice overall. It could easily pose for a brochure or magazine cover. As for the struts, I found on my Sherpa the Logo Evo's strut mounts were so narrow as prevent spacing them to reach the outside of the seatstay rack bosses, so I fastened them temporarily to the inside, which is too narrow to adequately brace the rack on my bike. My Sherpa is a 560S; your larger size may allow more latitude. I had the option of bending the stays as a pair or ordering the offset stays, and chose to purchase the models with 12mm offset, which will be perfect for mounting in the usual position.
Once I have the new struts installed, my next move will be to concentrate on tires.
Already, I have swapped the two Schwalbe Dureme 26x2.0 rigid (wire-bead) tires for a pair of folding (kevlar-bead) tires in the same size. The difference? The rigid models had a wavy tread cap, while the folders have a more centered tread with far less variation.
After I observe the results of that trial, I plan to rob the 26x1.5 road slicks off my tandem and mount them to Sherpa as a pair. Then (though the width will vary), I plan to put a 1.5 slick in front and a 2.0 Dureme in back, and the opposite -- a 2.0 Dureme in front and a 1.5 slick in the rear. The purpose? To exaggerate differences in trail resulting from variations in head tube angle and axle height.
I am still most puzzled by four things:
1) Why the bike does well with all the weight in the front and middle and *either* the 11lb rack-top load *or* the 25lb rear panniers, but *not both*.
2) Why the bike handles so miserably with no front load and more weight on the back; it is just not tolerating a rear load of any substance.
3) Why the bike initially did so well in road and off-road testing last Fall and Winter with this weight and more, but went bad with less on this last test-tour and thereafter. There are no signs of tube or joint failure, and nothing about the bike has changed. All appears to be solid and properly adjusted. It has never fallen over when parked and I have never fallen while riding it; it has never fallen at all. Everything seems to be properly aligned. Except for stiffening the sidewalls, changes in tire pressure seem to make no difference.
4) The same thing occurred with my '89 Miyata 1000LT following my return from one tour in preparation for another. It was as if it had developed a hinge in the middle of the top tube and all lateral distortion during shimmy took place there. I did take four hard falls on the bike during the last tour on it, and I will check the fork alignment to see if a blade has been tweaked forward or back compared to its mate. That is the only possible explanation I can think of for the Miyata, but none of that applies to Sherpa.
Best wishes for a safe, happy, and enjoyable tour, mickeg. Please let us know afterward how the change in racks does for you and how the bike handles with a load.
jags wrote...i often seen lads on old steel bikes with one or two bags touring the world how the hell did these guys do it, makes you wonder.
Yeah, me too, jags. I often think of Ian Hibell and shake my head in wonder. He surely did well, particularly on crossing the Darian Gap and the Gobi Desert.
All the best,
Dan.
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if you scroll down to the bottom of this page http://cyclotouriste.co.uk/index.htm you'll find reference to an article describing testing for shimmy. But possibly you know more than the author by now.
Ian
Thanks, Ian, for the reference; much appreciated. As it happens, I have now read the article and it appears Jan (Heine) is no closer than the rest of us in finding the definitive case or cure of shimmy. I do agree with his recommendation to use needle/tapered roller-bearing headsets, but for different reasons (longevity); a happy byproduct of their design and long life is greater friction. I do have one bike that developed shimmy only because of a brinneled (pitted) headset race; I happened to replace it with a Galli Supercriterium model with ti races and the problem -- nonexistent before -- was cured and never returned. The cause was definitely the pitted headset in that case. Not so Sherpa, whose headset is smooth and properly adjusted.
As part of his research, Jan (CompassCycles) posted two YouTube videos showing a bike where shimmy could be induced with the rider sitting upright and slapping his thighs. See: http://www.youtube.com/watch?v=vSNjpQPdrX4&feature=plcp ...and... http://www.youtube.com/watch?v=8pzc2aYVFEg&feature=plcp
At its worst, this is about the frequency and amplitude of my shimmy, but mine occurs when I am riding on the brake hoods or anywhere on the handlebars as well as when I sit up or even stand. It just happens when the rear load combines the rack-top mass and the loaded rear panniers together. With one or the other and a front load...no problem.
Any other ideas occur? I'm going to play with changes pneumatic trail due to differences in tire size as soon as the rack struts arrive.
All the best,
Dan.
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Dan,
I am having difficulty thinking of anything else which would help you in the quest for a solution.
One idea which popped into my head is that the shimmy is symmetrical, do you ride with exactly the same weights on the left and right sides of the bike?
Have you tried riding with more weight on one side? This might unbalance the shimmy and confuse it!
I sometimes take just one rear pannier for a shopping trip and end up riding carrying maybe 15 to 20 pounds on one side. My bike seems to cope with this and handles normally.
Just a thought.
Julian.
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Dan,
Thanks for the kind comments on the look of the bike. I bought the frame and fork used from someone that had the wrong size. The components were all my selection. It looks unusually clean right now because I gave it a very good cleaning as part of a detailed inspection I did of it after a bad crash I had in late May. Drive train looks unusually clean now too, I switched two chainrings less than 100 miles ago so they are quite clean, it is now setup for half step gearing (46/42/24 on front, 11-32 eight speed rear).
I use a different rack around town than I use for touring. And touring I do not use a rack top bag, so the width of rack top is less critical to me for touring. I might actually start using the Surly rack around town since it is the perfect width for one of my rack top bags.
I doubt that changing tire size will impact rake and trail enough to be noticeable in handling.
I will not be concerned if I have to mount the brackets to the seatstays on the inside instead of outside. If the seatstays had zero flex, you are right that attaching to the outer should be more sturdy. But, any flex in the seatstays may negate that making the specific attachment point less critical.
I think that sometimes shimmy which is a resonance problem may come and go with weight distribution.
I do not think spoke tension was mentioned, is your spoke tension right? I build up my own wheels and just use feel for spoke tension, I do not even know if any local shops here have a spoke tension gauge.
On my LHT, the shimmy was worse on pavement than on gravel. I think that the gravel allowed the tire to move slightly side to side as it rolled on loose sand grains, acting like a shock absorber on the resonance. That leads me to ask, have you tried to evaluate shimmy at higher and lower tire pressures? This is just a thought, I have never heard of tire pressure being a factor in shimmy, maybe it is not?
Also I suspect that the farther aft the center of gravity of the rear weight (panniers and rack top bag) is set on the rear rack could also impact resonance and shimmy. If you have excess heel clearance, maybe try moving rear panniers forward to get the center of gravity closer to the center of the bike?
Good luck.
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Dan,
Thought of this after I posted my note a minute ago. Since you have another set of wheels (on the tandem), if they have the same hub spacing, you can swap wheels to see if that changes things. If you try this be careful you do not accidently put your derailleur cage into the spokes in the event that the rear hub dimensions are different. If your shifters can be run in friction mode, you might not need to make any other adjustment changes for a short term test.
If swapping wheels fixes the problem, then it becomes an issue of trying to figure out why?
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if they have the same hub spacing, you can swap wheels to see if that changes things
An excellent, idea, mickeg!
The front wheel will swap right over, with identical spacing and Sun CR18 rim. The rear will have to be a tire swap, however, because the rear hub has much wider spacing and the Arai drag brake. The tire will go right over, though.
At this point, I really am just looking for change of some sort, either good or bad. Once I see what else affects the resonance of the frame (besides rear load mass and placement), I will have more direction. To that end, Julian's idea of trying a single pannier is also helpful (thanks, Julian!).
It is pouring rain at the moment, which complicates setup and testing, but hasn't stopped me. The weather 'round here is not reliably good until after the Fourth of July.
Pete, I especially like Jerome's hat-shaped helmet. I also notice he's moved his cargo weight toward the center of the bike as far as he can, so shimmy likely wasn't a problem for him (he just had to deal with little things, like having enough to eat and drink; how'd he ever?!?).
All the best,
Dan.
Thanks, fellows; your efforts mean a lot to me.
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:o "Arghhhhhhhhhhhhhhhhhhhhhhhhh!" >:( <-- Pure frustration.
Goodness, this is hard!
New Cargo Evo arrived. Same as the first Cargo Evo, despite a different description and stock inventory number in the REI catalog. Methinks REI is now stocking the large model as a "universal fitment" (as it says on the tube of parts attached to the rack) despite the two catalog entries. Makes sense and reduces inventory for them. Not so great for me, who required two go-'rounds to figure that out. Nobody at REI seems to know anything about it.
The offset Logo struts are at this moment at FedEx in neighboring Springfield, just 5.9mi/9.5km away. No, can't collect the envelope; hafta wait for delivery sometime before 16:30 tomorrow. Meantime, I can still try the too-large Cargo Evo, the Logo Evo, and the old Surly with various tire combinations and see what comes of it.
Onward!
Best,
Dan.
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hope you get it sorted soon Dan you must be cracking up at this stage ::)
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you must be cracking up at this stage
Well past, jags, well past. It is driving me crazy, and it's not a very long trip to get there.
If you see a man, running through the streets naked while playing an harmonica, chances are it will be me.
The neighbors will tell reporters, "Oh, he was always such a nice, polite, quiet boy growing up. Then...he got involved with those bicycle-things, and look what happened...".
Dan.
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Hi All!
Executive summary: Thankfully, I can report success - the Sherpa Shimmy is banished! At least for now, pending further testing.
My faith in the value of good research methodology has been confirmed by this experience. Because at present I am uncertain exactly what made the difference, I will continue testing tomorrow to make sure the success is repeatable at higher speeds (Green Hill, here I come) and then I will deconstruct what I have to see if the shimmy reappears.
Yes, with this much weight, yanking the handlebars back and forth rapidly can induce a brief oscillation visible as a low-frequency, low-amplitude sine wave in the top tube, but it is self-damping almost immediately after the inducement has ceased. The same effect can be achieved at rest so long as the rear brake is locked, forcing the rear tire to serve as a pivot point for "winding up" the top tube, which serves as a self-correcting linear spring. Neither of these deliberately-induced states manifested as shimmy when riding.
For those hardy souls who wish to learn more, here's a summary of today's efforts in excruciating detail:
In our last installment, I got Sherpa to the point where he just barely didn't shimmy with the minimal load I can take, but no more. He wasn't very pleasant to ride, and I wouldn't have had the water or food needed for extended desert crossings.
Here's what I did today, in order; something or some combination has worked:
1) The 12mm offset front stays arrived this morning for the Tubus Logo Evo. They were the perfect size to reach the outside of the rack's mounting holes and the outside of Sherpa's seatstay bosses, remaining parallel. As expected, they made the rack much more rigid at the front than it was before. Still, the rear of the rack is as flexible laterally as the Surly Nice Rack (Rear). The Cargo Evo is much more rigid laterally overall, thanks to its inverted U-shaped rearstay configuration. The rear panniers are mounted to the lower rail of the Logo Evo, as designed.
2) I swapped the rigid (wire-bead) 26x2.0 Schwalbe Duremes with the folding (kevlar bead) version in the same size. As with the rigid tires, I followed Andy Blance's recommendations and set maximum tire pressure as per his chart on page 6 of the Nomad brochure (Issue 17c, Summer 2012,
http://www.sjscycles.com/thornpdf/ThornRavenNomadBroHiRes.pdf ): F: 45psi/3.1bar R: 51.5psi/3.5bar. Actual section width and profile at this pressure is 47mm (100% section width/profile).
RESULT: Reduced nervousness and the feeling I was farther from shimmy.
3) I then added weight to the rear panniers, ballasting the rear panniers so they weighed as follows:
Left-Rear: 17.27lb/7.84kg
Right-Rear: 17.17/7.79kg
(Paired rear panniers: 34.61lb/15.70kg...some rounding error, but I weighed the pair directly).
All other loads on the bike remained constant in mass and placement as before.
RESULT: Same as 3) above.
Feeling I was about topped-out on trials with this setup (tired and not wishing to see my teeth spread on the ground like a spilled box of Chiclets), I then decided to change tires. Off came the 26x2.0 folding Duremes and on went the (Trek) Matrix Road Warrior skinwall slicks, labeled 26x1.5, but with an actual section width/profile of 37:37mm in front and 38:38mm rear when inflated to Andy Blance's recommended maximum of: F: 63psi/4.3bar R: 70psi/4.8bar
Result?
I then went out on the unladen bike to check the feel, and it was transformed! From touring bike to high-speed randonneur in one go, even with the heavy Rigida Andras! The difference in acceleration was absolutely amazing. Of course, I reset my computer to the new tire size (and recalibrated it again when I piled on the load a little later so I could account for extra tire squash due to the greater load) so my speed measurements were accurate. For those interested in coast-down data, the 2.0 Duremes were about on par with the slicks in coast-down. I'm intrigued enough that I want to replicate those tests later, but it looks as if nothing much is given away by the fatter tires on coast-down. The difference in acceleration and lively feel made the slicks the hands-down winner in that category. I could easily see Sherpa as the bike for my next 24hours/400km ride through the mountains. The fenders had ungainly clearances, but who cares when the bike flies on acceleration and winds-up far more quickly even though coast-down is very similar if not almost identical? Leaving the fenders high means no adjustments when swapping to 2.0s again.
Some caveats wrt the swap from 2.0 to 1.5 tires:
1) It is important to remember the change in feel is not due simply to the slick tires being narrower at ~37mm vs ~47mm width.
2) The slicks are also lower in profile by the same 10mm amount in radius (remember the typical 1.0 relationship between tire section width and profile), twice that amount (20mm) in diameter (which is why I had to recalibrate the computer).
3) The lower profile effectively changes the geometry of the bike by changing the pneumatic trail, as discussed in my earlier thread here:
http://www.thorncycles.co.uk/forums/index.php?topic=4245.0
Just how much did the lower-profile tires affect my Sherpa's frame geometry? On my 560S with the same frame dimensions and fork offset as before, trail was reduced from 62.93mm to 58.68mm, effectively moving the bike from a high-trail state, smack-dab into the neutral-trail/neutral-handling zone. The bike was noticeably less "twitchy"/maneuverable at low speeds, and a bit less "on-rails" stable at higher speeds, just as expected. It was more inclined to lean into corners and less likely to prefer the "sit up straight and steer the bus" approach. Wheel flop at low speeds was considerably reduced. A very sweet ride indeed, and very like my 1983/84 Centurion ProTour 15 go-fast randonneur bike, which uses 700x32C tires and a geometry different from my stock Sherpa with 26x2.0 tires.
4) The slicks are also treadless; these in particular have a bare skim or rubber atop the casing for tread and are completely smooth and unbelted. No wonder the tandem flies on them.
5) The slicks are also considerably lighter. They are mounted now and I overlooked weighing them before mounting, so that task lies ahead.
6) The slicks' shorter sidewalls and narrower width and lower profile and lack of tread and higher absolute pressure *together* mean there is less sidewall "wiggle" than on the 2.0s. In other words, the 1.5 slicks' pressurized tire casing is noticeably and measurably less flexible laterally than the 2.0 Duremes.
I reloaded the bike with the same load and placement as before, and there was no sign or shimmy and everything felt much more stable and less "nervous" at speed, and there was less wheel flop at 2.5-8.5mph/3.9-13.7kph. Again, all as expected by my trail calculations. Nearly drunk with joy at the first truly positive change since testing began, I replicated all the prior loaded testing with the 1.5 tires and the bike passed with flying colors and no shimmy. Besotted with happiness, I then decided to deliberately add the 10l MSR Dromedary loaded with 6l in the *worst* possible place -- *atop* the rack-top load (above the sleep system dry sack and tent, shown in the photo below). The MSR Dromedary with 6l weighed 13.8lb/6.3kg, right up-top. Even with the water bladder placed high, the bike handled well at 25mph/40kph on smooth and wavy and rutted asphalt, and at much slower speeds it also did well on deep grass, across a stretch of muddy dirt, on gravel, and across a former plowed field.
The only anomalous observation came after repeated high-speed braking at the end of each speed run, when it became evident the bolt-on skewer for the SON28 dynohub loosened. It is possible it was the core culprit in the original shimmy, but this seems unlikely as the hub's skewer bolt felt adequately tight when I removed the front wheel to change tires. In the even it is a contributor, I have replaced the bolt-on skewer with a Shimano q/r unit I have measured and calculated to maintain adequate skewer clearance to allow the hub to "breathe" properly and prevent suction of water past its shielded cartridge bearings' seals. Schmidt Maschinenbau specify...Schmidts Original hub dynamo SON 28 fits a fork designed to accept an axle of 9 mm diameter and a width of 100 mm between dropouts. The electrical connections should be on the right hand side (to prevent unscrewing of the hub). The hub is secured using the included skewer set. It fits the same way as a quick-release, but fastens with a 5 mm allen key (recommended torque moment 6 - 8 Nm). Apply a little grease on thread and screw-head but not on the shank(to prevent clogging up the pressure compensation system leading into the hollow axle). If the skewer tension is too low, the axle may move inside the fork end causing a rattling noise. Alternatively a lever-type quick-release may be substituted, or a proprietary security fastener such as Pitlock.
Because the bolt-on skewer was found loose after the *final* (successful) testing, I cannot discount the possibility it was loose originally, accounting for the small positive change I attributed to the switch to the folding Duremes (I had to re-tighten the skewer after the tire change). With the q/r in place, I now have a baseline for running the original tests once again for comparison. Given Sherpa's initial ability to handle very large loads with aplomb and the subsequent appearance of shimmy, skewer tension cannot at
this time be dismissed as a possible contributor. Certainly, for failsafe tensioning of the wheel, the q/r skewer's over-center action is ultimately more secure than the bolt-on variety, particularly given the M5x.8 thread pitch used and the low recommended tightening torque of only 6-8Nm (4.42-5.9 ft-lbs). By the way, the SON's bolt-on skewer was tightened to spec with a torque wrench each time, and before the appearance of the original shimmy.
Tomorrow's going to be a very long day of testing up and down some very steep grades with maximum full load as if for an extended desert crossing. I'll be cautious with my run-ups and coast downs and check the load and skewer tensions after each run. I should know something more definitive afterwards. If all goes well, I will swap the Surly rear rack for the Logo Evo and see what effect it has. Yes, it is worth the effort for standardized, repeatable results. It wasn't so much fun during periods of pouring rain today, but tomorrow is supposed to be better, and my spirits are much higher as a result of today's efforts and positive results.
Thrilled as I am with today's outcome, I still want to get to the bottom of identifying the culprit or contributors and address them so I can cure the problem at the root and not simply apply a plaster to the problem.
I'd also like to get those folding or rigid 2.0 Duremes back on for the places I'll be going, and to also determine if the rigid versions are truly warped/belt-shifted/whatever or if something else was in play.
Getting there!
Best,
Dan.
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Congratulations, Dan. With much relief I'm off to bed, my last thought no doubt, "I told him a systematic approach would see him right." Heh-heh. -- Andre Jute
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Andre,
My sincere thanks to you and to every single contributor to this topic. You have all been so very good to offer encouragement, hope, suggestions, and most welcome and much-needed humor and distractions. Truly, "Thank you!" ;D
Some really good suggestions, from all and well worth summarizing for others who may someday encounter shimmy:
Pavel: Rear rack bolts loose?
Richie: Check the wheel fasteners.
Andre: Weight distribution.
Jags: Headset tight? 'Bars centered? Try swapping wheels.
Julian: Check the rack-top load, bring rear weight forward as far as possible, change size of load.
JimK: Use a "tell" to check for rack shimmy.
Pete: Maybe rack contributes; definitely check load distribution.
Pavel again: Get a Nomad! (will, when I can!)
Stephen: Suspects the rack-top bag.
Rual: Overloaded/mis-distributed?
Pete again: Nomad! And...ExtraWheel trailer! (Alright! Yes! Yes to both! Just need mun-mun!)
JimK again: Try using free-weights to simulate a load/problem.
Stuart: Pneumatic trail (via email).
Ian: High cadence?
Julian again: Try swapping tires F/R.
Mickeg: Maybe the Surly rear rack?
IanS: Article on shimmy causes.
Jags again: Weight too much?
Julian again: Try asymmetrical load to see if it helps.
Mickeg again: Spoke tension? Try moving weight to center, swap wheels.
This shimmy really put me through the wringer, but I'm coming out the other side, thanks to sheer cussed determination (and a systematic approach, Andre). I've got a ways to go yet, but this is really encouraging. Off to sleep myself, as I only saw my bed last night from 3:30AM to 5:30AM and I need to make up for lost time...and it's well into tomorrow again here already.
Oh! For those who are interested, the maximum successful test weights and distributions are shown in the diagram attached below and match the load pictured in the last post. No problem at all at the conclusion of the last tests, even off-road. Of course, I do not plan to ride regularly with such loads, but it is nice to see I can when needed. It's that water and extra food for the extended desert crossings that are responsible. Sans food and water, I'm right at 42lb/19kg for living on the bike indefinitely in all seasons. Even that I could get down a bit if I didn't carry 3 cameras and batteries for them and a mini-tripod. And the chair. Gotta have the chair.
All the best, and thanks to everyone again!
Dan.
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Congratulations Dan. I hate to say it, but I have been watching with a morbid curiosity; the rigour and scrutiny of your testing as recounted on here always brings a smile to my face. But I am happy your woes are over now!
Phil
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...I have been watching with a morbid curiosity...
You're not alone, Phil; I would have done the same. Such problems are somehow more fascinating when they're not one's own! Still, the topic has always interested me, and this was a um, "growth opportunity". Perhaps the lesson for me should be, "Careful what you wish for!" :DCongratulations
Thanks! It is so nice to near conclusion on this one.
I still wonder if that SON bolt-on skewer was a primary trigger in the original shimmy. I can't go back in time, but I can restore the initial configuration one piece at a time and see if it comes back. I'd like to use those Duremes and shoot out the door and into my tour in what remains of my time window. In future, I think I'll follow jags' lead and see if I can find a good price on some light 1.5 road slicks and superlight tubes for the occasional long-fast blast on Sherpa. He was simply transformed in terms of acceleration when I swapped tires. Wouldn't be as happy touring on them with a load, but otherwise...! Also want to replicate those comparative coast-down tests elsewhere.
All the best,
Dan.
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Dan i knew that was te problem all along just wanted you to suffer a wee bit. ;D ;D ;D ;D ;D
only jokeing my friend well done i'm sure robin thorn is also somewhat relieved ;)
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Well done Dan
you are nothing if not thorough, not to mention "careful".
Both the suspect areas you have identified (tyres and skewer bolt) have caused me concern in the past.
I originally built my Sherpa with 2.0" Marathon Supremes and found that on a narrow rim (19mm Etrto) they were too flexible in the sidewall unless pumped up to 65psi plus, thus rendering them hard/uncomfortable/pointless as well as heavy. I only use it for hilly rides with no touring load. I think 2.0" really need a wider rim to work. I now run 1.6" Supremes at LOWER pressures 45/48psi and more comfort on the same rims, but they are faster, much lighter and handle better. I'd like a 1.6" Dureme for winter but they don't make it.
In light of your steering/trail article I think handling improved because the bike was designed around 1.5 and 1.75 tyres and stretches to the now more fashionable 2.0 at the expense of handling finesse. Schwalbe used to make the old Marathon XR in 1.6 but not so any of it's newer replacements..... inflation of a sort.
When you see all the "lighter than Shimano" (cheaper to make) skewer reviews in webshops they all have a long bolt in torsion that many people snap! I'm suprised you weren't using a Shimano skewer in the first place as they are torsion free and therefore tight/reliable and no windage to slacken them off in use. Usually you seem to have covered EVERY angle in advance by yourself.
Fingers crossed, let's hope you remain wobble free
Ian
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Great work, Dan! Just so very excellent that you not only solved your problem but pointed the way for the whole community. I don't push my bike's limits so the 50mm tires on 19mm rims doesn't cause real trouble. But I've been considering tires more in the 40mm zone and your experience sure adds fuel to that fire!
I'm really happy to see you get your set-up working properly!
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Hi Ian!
Well done Dan
you are nothing if not thorough, not to mention "careful".
Thanks! Also relieved to be this far along in the process and with a positive outcome.
I think handling improved because the bike was designed around 1.5 and 1.75 tyres and stretches to the now more fashionable 2.0 at the expense of handling finesse.
Exactly the same thought I've been having, Ian. I have a ultimate solution in mind for that, but I'm not quite "there" yet in testing to confirm it.
It is also worth remembering that we're talking pretty large differences in both tire width and profile here compared to road bikes. I can really notice a difference in handling on my road bikes when I switch from one 28mm tire to the identical model in 32mm, and that's just 4mm difference. When I changed from the 2.0 Duremes (at 47mm) to the 1.5 Matrix Road Warriors (at 37mm) are a whole centimeter different in width and sidewall height (profile). It's a big jump. I really see the difference when I look at the empty space between the tires and the fenders with the 1.5s in place. The difference looks even greater than it is.
I originally built my Sherpa with 2.0" Marathon Supremes and found that on a narrow rim (19mm Etrto) they were too flexible in the sidewall unless pumped up to 65psi plus...
Yes, Ian, I agree; the 2.0 Duremes I regularly use are a great source of lateral movement, and the culprit is the sidewall. I do believe this is also the reason for their relatively low rolling resistance, but it comes at a cost in lost lateral stability under heavy load. I found the same as you -- stiffening the sidewalls via elevated pressure soon led to diminishing returns. Now, of course, I want to tease out just what result is due to which factor. I wish I had a 1.5 Dureme at my disposal for a direct comparison, and set of 1.75s as well. In my case, I had the 1.5 slicks ready-to-hand on the tandem and they were enough different from the 2.0 Duremes I figured if there was a difference, it would be large enough to tell me if I was on the right track.
When you see all the "lighter than Shimano" (cheaper to make) skewer reviews in webshops they all have a long bolt in torsion that many people snap! I'm suprised you weren't using a Shimano skewer in the first place as they are torsion free and therefore tight/reliable and no windage to slacken them off in use. Usually you seem to have covered EVERY angle in advance by yourself.
Well, I had "help" in this case in the form of the SON product information guide. It makes such a point of the very low tightening torque needed to secure the hub, and with good reason. The thrust spacer between the bearings is not as one would expect in, say, a Phil Wood hub and it is easy -- oh, so easy! -- to overtighten the skewer and pre-load the bearings in a way that would lead to a quick demise of the hub. Because of that, I went with the Schmidt-supplied bolt-on skewer so I could install it with a torque wrench and stay on the right side of things. In my case, it doesn't seem to be working well insofar as staying tensioned properly. I do *not* want to risk a front-wheel loss (enough whole-face reconstructive surgeries and five broken noses behind me already), so it is back to a standard q/r. I wholly agree with your comments on the dangers of boutique q/rs and avoid them like the plague. The closest I have come is the old Sachs Quartz series of external-cam q/rs that reside on my two Centurions and the in-progress Folder build, but those are all used with vertical dropouts and I have tested them over a very long period and to measure the clamping force. Otherwise -- despite all the prettiness, as you've observed -- it is awfully hard to beat the traditional old-school internal-cam q/r for reliability and maximum clamping force. I broke my own rule in trying the SON bolt-on skewer, but I'm back on-track now. Fingers crossed, let's hope you remain wobble free
Thanks so much, Ian; I'm hoping too! I'll take it easy and ramp up gradually on my downhilling efforts. I've had my unloaded single bikes up past 58mph/93kph on Green Hill, and it might hurt Sherpa if we went down at that speed, so caution is well-advised.
...not only solved your problem but pointed the way...
Thank you, Jim; I think there's Bigger Lessons hiding in here for all of us. I know I've learned volumes just by keeping the permutations logged and straight and noting the results. It really helped to have a modular load, so I could add or subtract at will. Though the problem is technically solved for me at present, I'd still like to use those larger 2.0 Duremes for this next tour, and I want to really tease out the root cause. It still niggles the corner of my mind that I might have missed a possibly loose bolt-on SON skewer to start with...otherwise why the sudden appearance of shimmy with a lesser load when there had been no sign of it with more. I do believe there are many causes of shimmy, and there is no one universal solution. Still, it would be really nice to develop a laundry list of ranked, discrete causes so others could try them in order instead of taking shots in the dark.
I've been considering tires more in the 40mm zone and your experience sure adds fuel to that fire!
If you can possibly borrow or try a set of narrower ones, I think it would be worth it, considering how completely they transformed the bike with the same heavy Rigida Andra rims. It was really unbelievable. Of course, the smaller-diameter tires required a computer recalibration, but they also required a physical and mental one. I was flying along one gear higher, wondering if this is what blood-doping feels like, when I realized the tires had also effectively lowered the gearing. I could see the need to go up or down one chainring tooth-size on a Rohloff bike that went from one extreme in tire width/profile to the other.
All the best,
Dan.
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Dan i knew that was te problem all along just wanted you to suffer a wee bit only jokeing my friend well done i'm sure robin thorn is also somewhat relieved
'Missed this one! Jags! I should be thanking you for the "growth opportunity"! ;) Actually, I'm almost sick with relief to be at this point in the game. It's going to be a busy day for myself and Sherpa as soon as the cold, gray fog burns off a bit and the temp goes above 50F/10C. I want "warmer" for blasting downhill at speed!
Best,
Dan.
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Dan i knew that was te problem all along just wanted you to suffer a wee bit. ;D ;D ;D ;D ;D
only jokeing my friend well done i'm sure robin thorn is also somewhat relieved ;)
Laughing out LOUD!
And out of vast RELIEF too. A sickening experience, I'm sure, now that we can laugh about it; nobody wants his holiday ruined.
Thanks for taking the time through all your travails, Dan, to keep us informed as to method and findings. Though we all hope never to stand in your shoes in a like matter, who knows what fate brings?
Andre Jute
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Hi All!
All went well with high-speed testing down Green Hill today. Weighing 154lb/70kg for bike and load (including 16.5l of water and extra food, configured for extended desert crossings), Sherpa managed 53.5mph/86kph and was stable as could be, with no sign of shimmy.
For photos and a ride report, see my gallery entry at: http://www.thorncycles.co.uk/forums/index.php?topic=3896.msg20459#msg20459
Tomorrow, I'll fit the rigid 2.0 Duremes and see what happens on another 3 rounds of the Green Hill Challenge.
Best,
Dan.
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Laughing out LOUD!
And out of vast RELIEF too. A sickening experience, I'm sure, now that we can laugh about it; nobody wants his holiday ruined.
Thanks for taking the time through all your travails, Dan, to keep us informed as to method and findings. Though we all hope never to stand in your shoes in a like matter, who knows what fate brings?
Andre Jute
Echo Andre's sentiments, I couldn't put it better.
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Dan,
My Logo EVO arrived today. Photo shows it installed. Fortunately I had some spare allen head M5 bolts so I could avoid the Torx 20 bolts. (What where they thinking?) Have not ridden it yet, sun was down when I finished getting it installed, will try it tomorrow, but already if feels a bit stiffer than the Surly rack.
In the photo, note that I am staying with the provided brackets (roundstays) and installed on the inner parts of the attachment points. Used hex bolts instead of allen head bolts there. (The other bolts on the other ends of those attachment points is where I carry some of my spare bolts in case I lose a bolt on tour.
Two suggestions for your setup:
1. Use blue locktite on all rack bolts unless they have nylock nuts in which case they do not need locktite. You do not want a rack bolt to fall out.
2. You can't really see it in my photo, but near the ends of the "roundstays", just inside where the little rubber caps are shoved on, I have wrapped electrical tape around the stays. A few years ago I read on the internet that some gal was riding home with her new Surly rear rack and the little set screws on the rack bracket came loose, the rack rotated backwards so that the rack was only attached to the bike at the two bolts at the dropouts. The stainless hardware that attached her stays to the rack went flying to who knows where. The rack jammed on her tire and effectively stopped the bike. I wrapped that electrical tape on so that if the bolts that hold the roundstays to the rest of the rack come loose, the rack can rotate back but not completely off of the roundstays, thus no parts would be lost.
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Fortunately I had some spare allen head M5 bolts so I could avoid the Torx 20 bolts. (What where they thinking?)
They assume that, if you can afford one of their racks, you have a Rohloff hub gearbox on your bike as well. Rohloff owners carry a T20 tool or bit. SKS even supplies a swap-in replacement T20 arm for one of their multitools. – Andre Jute
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Hi All!
For those still following the Sherpa-shimmy thread, work continues with definite progress.
I am very close to identifying a root cause and solution in my own case, and the overall shimmy research should start paying some benefits I will share as soon as the factors are data-confirmed to my satisfaction. The results at this point are surprising to me, but empirically supported by the data.
I think the factors involved are present but largely unproblematic at all loads and are amplified and become apparent or problematic as a function of carrying very heavy loads. If true, these factors would become important with any combined mass of bike, load, and rider approaching or exceeding the total I am carrying and are affected by weight placement and distribution in unexpected ways. Carrying a very heavy load may precipitate shimmy and provide a shortcut to its resolution, as any low-level normative factors are amplified.
I am still slogging up and blasting down Green Hill as I near a conclusion, but that effort has been halted temporarily by heavy rain. I don't mind riding in the rain, but I don't relish the idea of descending in excess of 50mph/80kph in a downpour with small herds of deer and flocks of wild turkeys about the road and a touring bike I'm now actively trying to make shimmy at speed. Also, the research has expanded to include my Miyata 1000LT, whose shimmy developed and manifested very like Sherpa's and, I think, for similar reasons.
More as soon as additional data are collected and analyzed.
Best,
Dan.
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Hi All!
I now have an update on the Sherpa-shimmy problem, and unfortunately, all is not well. The executive summary of continued testing follows:
1) The bike still shimmies with any reasonable rear load, and it shimmies with a total load at the levels referenced by Andy in the Summer 2011 brochure used when I ordered my bike last August.
2) Water placement and mass has essentially no negative effect on the shimmy; if anything, the steerer-mounted bottles damp the shimmy. This was a surprise to me.
3) Unlike a more conventional shimmy, it does not resolve with changes in rider position, letting go of the handlebars, or standing. The result is pretty scary.
4) I can *just* drop the bike into a consistent no-shimmy state with a full load *if*...
a) I fit a Tubus Logo Evo rear rack and fit the panniers on the lower rail,
*and*
b) Fit the 1.5in road slicks borrowed from my tandem, keeping the inflation at maximum pressures described by Andy in the Thorn brochures.
The rack change helped a bit on its own, but not enough to fix the shimmy outright. The larger positive change came with the change to narrower/lower-profile tires. I believe it is because they also had the effect of changing the effective trail, dropping the geometry into neutral-trail territory from the high-trail that occurs when 2.0 tires are used. Switching back to the 2.0 tires showed over-lively low-speed handling and a marked increase in wheel-flop at rest, as expected of the higher trail.
With this thought in mind, I sent for a replacement fork with 59mm offset, versus my standard 52; when fitted with 2.0 tires, the maths show it would have essentially the same trail as when the stock fork is fitted with 1.5 tires. Unfortunately, I have been unable to fit the replacement fork due to problems in shipping and the product itself. I still hold hope it might be the answer that would allow me to tour with at least the recommended load and wider/taller tires offered as an approved option.
Still, if such heroic measures are required, I am concerned it signals a problem with my Sherpa example. All testing results point to a persistent problem when weighting the rear, yet a careful examination shows no outward signs of damage or breakage to the frame. Remember, it rides fine when unladen or with a small load (25lb/11kg ) distributed between the handlebar bag, bottle cages, and rack-top pack.
Continued testing did reveal some additional surprises for me...
5) Thinking my long-steerer might be a problem, but it was not. I juggled the spacers, dropping the stem to very near the Thorn Accessory T-bar, which sits just above the headset race. I inverted the stem and I tried moving it up ad down a spacer at a time. No change. I found this surprising until I recalled that a change from hoods to drops or even sitting upright or letting go of the handlebars also made no discernible change in the onset or continuation of shimmy.
6) Thinking rider mass might be a factor, I added weight to various parts of my body using a fanny pack and the lower portion of a small backpack. No change. I am 5'11"/180cm in height and weigh 172lbs/78kg, right on average for my age cohort. Still, I have a number of friends who are far heavier...I purchased my tandem used from a family whose members all weighed in excess of 375lb/170kg, and it had no problem at all handling that combined mass plus a day-riding load. Perhaps I'm making a leap in logic, but it seems reasonable that if I am of average weight for my age/height cohort, then I would also be of average weight for a properly-sized bicycle like this one. Getting heavier didn't make a difference, and I can't get lighter!
That said, mass on the bike -- and apparently at the rear -- makes the deciding difference in handling and shimmy for my Sherpa. Unladen except for about 35lb/16kg in rear panniers, the bike's handling is really unpleasant and squirrely...moreso than when a similar load is placed only on the rear rack of my other touring bikes with conventionally-sized road bike tubing. In contrast, with only a front or front and mid-load (three 1.5l bottles in the main triangle of the frame), Sherpa's handling remains sweet as can be. The same goes when either a rack-top load is added or rear panniers are added. Things go bad when an upper and lower rear load are carried regardless of whether a front or front and mid-load are carried. This has been a consistent factor throughout all my extensive testing, and is repeatable.
By the way, I have been able to stand with a touring load when pedaling up to speed but standing does not stop the shimmy once it occurs.
Though I can't make it do so consistently, I get the feeling the bike would like to pull left against the road crown when riding with no-hands and a touring load. I have not noticed this when unladen, but I rarely ride no-hands. Just a data point to keep in mind. Yes, both wheels are properly tensioned and true, and centered in the same plane (between the dropouts). This feeling of pulling left was more pronounced with the 2.0 tires (wired-on and folding) than with the tandem's 1.5in road slicks, but remember...the narrower tires also have a lower profile and do significantly affect trail.
7) A definite surprise for me was the involvement of the Schmidt/SON dynohub bolt-on skewer. Though it has standard threads, it lacks nylon inserts to prevent loosening and because it screws to tighten, it is impractical to fix in place with LocTite. Schmidt's package insert for the hub and a reference on their website both clearly indicate a maximum tightening torque of only 6-8Nm (4.42-5.9 ft-lbs). By the way, the SON's bolt-on skewer was tightened to spec with a torque wrench each time, and before the appearance of the original shimmy. Nevertheless, I often found it had loosened after my test runs, and soon removed it and replaced it with a conventional Shimano quick-release. Thanks to its over-center action, the q/r has never loosened in subsequent runs and has not proven to be a factor in shimmy. I am not entirely sure what caused the loosening, whether it was the low recommended tightening torque, the lack of a nylon insert for the nut, the violent action of the shimmy, the weight carried, or some interaction of all the above. Given my experience with the SON bolt-on skewer, it might be a Good Idea for others using bolt-on skewers (i.e. Pitlocks) to give them the occasional check just to be sure they're still tight. Unlike with a q/r, there is no visual indication of tightness with a bolt-on skewer. I've also heard no reports of Pitlocks loosening, so my SON problem may be isolated.
8 ) The front fork blades on the original fork are about 2.5mm wider than the SON dynohub's 100mm, so any wheel inserted into the forks draws them closed when tightened. I don't know if this is a factor or not. The dropout faces appear parallel when the wheel is secure. I think both fork legs are in the same plane (one blade isn't ahead of the other), but this is hard to determine on the bicycle. I had hoped to determine this when I changed forks, but that has to wait a bit. The replacement fork is also spaced a bit wide.
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I've certainly learned a lot about shimmy and collected a great deal of data on it in my tests. Still, I do continue to have a problem with it and would dearly love to get my beloved little Sherpa to carry at least a reasonable and recommended load without shimmy. If it would also carry the same weight as my old Miyata 1000LT with conventionally-sized tubing, that would be ideal.
I have waited so long to contact Thorn about it because I wanted to make absolutely certain the shimmy was not the result of some inadvertent action on my part, or due to a mistake in load placement or mass distribution. I had such high hopes that might be the case. By bringing the shimmy issue to the Forum, I hoped members might come up with a solution to the problem. Thanks to extensive testing, I'm now beginning to conclude there is something wrong with my sample and I will need Thorn's help to resolve it.
Best,
Dan.
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you just got a faulty frame dan simple it happens.
the problem you also have is sendind that frame/fork back to sjs cycles it wil cost you a bloody fortune.
unless of course sjs cycles are willing to admit the frame is only fit for the bin and they shoul send you a new one today .
best of luck dan i hope you get satisfaction real soon.
i'm off to donegal now hope to hear about your new frame when i return. ;)
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No personal experience Teh Googles say...http://www.sheldonbrown.com/brandt/shimmy.html
2) Water placement and mass has essentially no negative effect on the shimmy; if anything, the steerer-mounted bottles damp the shimmy. This was a surprise to me.
Maybe this dampens the front wheel oscillations? As it essentially puts more weight through the front wheel?
I hope it all gets sorted, it's a nightmare to ship items from the USA back to the UK :(
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As a company we normally leave the forum to everone else, as a result this is the first I've seen of this thread. AndyB our designer is dealing directly with Dan to resolve his issue, no doubt Dan will post more later when we resolve it, one way or another! Rgards Robin Thorn (CEO).
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Hi All,
A little update...
The replacement fork and a Thorn EX rear rack arrived by post Saturday. I fit the rack without incident Sunday, and spent a good bit of time testing it Monday, with the video results here:
http://www.youtube.com/watch?v=0TB5TonYKjQ
http://www.youtube.com/watch?v=GwHI_uU4xLA
http://www.youtube.com/watch?v=aE_oeoDAEqo
Shot with my GoPro Hero2 HD vidcam and chest-mount.
The shimmy is worse, and present at low-speed (didn't want to try high-speed). It is bad with the higher weights I would carry on my solo desert tours as well as at lesser weights. Water inclusion/placement didn't trigger or address the shimmy, though the shimmy was faster (higher frequency and a bit higher amplitude) with no water. Removing the handlebar bag didn't help. Again, the problem seems directly related to rear loads. The shimmy emerged as soon as I gained forward momentum and persisted thereafter.
Though very hard to control, oddly enough, the bike still travels pretty straight while shimmying. I swapped to one of my other bikes, and I tried to deliberately jerk its handlebars from side-to-side. I couldn't do it at anywhere near this fast or evenly, and the bike darted across the street in a new direction each time. Gripping the handlebars tightly, holding tight or loose with one hand, or even letting go completely makes no difference. Neither does standing up on the pedals (unweighting the saddle) or pushing a knee against the top tube or gripping the top tube by hand.
I have not yet fitted the higher-offset/lower-trail 59mm fork.
Best,
Dan.
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Hi Dan saw the vids on youtube...
My purely out of mathematical interest points :)
Never had shimmy on any bike I ridden (luckily!) so am looking at this from a google/maths POV and hope it can help give you ideas.
Youtube: When full front load, all bottles, and *either* a rear rack-top load *or* rear panniers are carried, handling is OK. When a load is carried atop the rear rack *and* in rear panniers, shimmy occurs. A rear load *only* is also unstable, and difficult to ride.
That's strange as "in theory" (and we all know what that means as bumblebees couldn't fly in theory until they updated theories on lift ;)) load distribution should not matter and you tried the usual things already (move, stand up, leg on top tube)
Your post: Water inclusion/placement didn't trigger or address the shimmy, though the shimmy was faster (higher frequency and a bit higher amplitude) with no water.
That makes sense again per theory as it weightens the frame, thereby making the "spring" (the frame) heavier and stiffer. So it needs can't vibrate as fast as the vibration energy needs to move more weight back and forth. #Math people apologies for fluffy wording
My two cents is that the energy in the frame must be stored somewhere near the back, with the spring being the frame, and the mass being the back load. As front loads are ok, but once you put a lot of weight on the back the shimmy starts. So I guess the vibrating point is somewhere near the seat stay...behind where you sit. Without weight to give the frame a point to vibrate along (eg no load on back, as you sitting down it won't happen) the shimmy can't start.
Well that's all I can say from a theory analysis...hope it helps! :)
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A shimmy can happen without there being any kind of spring involved. It can come purely from the way the frame geometry and weight distribution play against the steering and how the bike tracks. This is how I understand Dan's theory about the fork, trail, etc.
Bikes tend to be dynamically stable. If a bike tips to one side, that will cause the front wheel to turn in the direction of the tip. The front wheel will then track along the pavement to put itself back under the bike. As the bike returns to being upright, the wheel needs to straighten itself out somehow. It might overshoot a bit but as long as the back-and-forth gets smaller quickly, there won't be a problem. But if the front wheel is too slow to steer back straight as the bike becomes upright, then the bike will end up leaning too much the other way, finally causing the front wheel to steer back the other way. If each cycle of correction and overshoot gets worse, the shimmy will quickly get so bad that the bike will just fall over. In a shimmy like what Dan has, somehow a small oscillation gets amplified but then larger oscillations somehow hit more damping or some other limit, so there is a kind of dynamic stability to the shimmy.
Of course frame flex can get mixed in here somehow. The front wheel could steer itself under the head tube but the rear load might not come back over the rear wheel right away - that bit of lag could prevent the front wheel from straightening out soon enough.
I sure hope Dan gets this figured out soon, though! It is a difficult problem but a nasty obstacle too. Bicycle mechanics is interesting for a little while but then it is really much more fun to get out and ride!
.
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boy's and girls you can talk tech stuff until the cows come home ,the frame is faulty it's really that simple why the hell no one else can see this is a total mystery to me .
for what it's worth i loaded up my sherpa with all the gear i have no idea on weight but yeah it was heavy ,well the bike was solid not a sign of a shimmi .
the frame dan got has to be at fault no other reason for it...
but theres a simple solution to all this Thorn send that man a new NOMAD
DAN have you a good hacksaw in your garage. ;)
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for what it's worth i loaded up my sherpa with all the gear i have no idea on weight but yeah it was heavy ,well the bike was solid not a sign of a shimmi .
Yeah this is the real test for a faulty frame. If you can put on the same load as Dan but get a different behavior, then Dan has a frame with a manufacturing error or it broke in shipping or at some point. Ah, but it would have to be the same size frame too. The frame size will affect the handling.
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I am assuming Dan already tested for a broken/damaged frame..if not maybe the gentle tap on the frame test can reveal any cracks etc..
See Jags is only 1.67/5.6 maybe that's why he gets no problems ;D
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I have to be careful here because I'm a guest (I don't have a Thorn, though it is on my shortlist) and have taken much away from the Thorn Forum.
Just as a matter of interest, Jawine has a point; from automobile practice, I would say that the tyres can be modelled as a spring, and the frame to a lesser extent. I'm not saying it is a helpful analysis -- in my book about building prototype cars I showed how very non-linear these problems are even when you have four wheels on the ground -- but merely that there's a little theoretical truth in it. In any event, in his thorough experiments, Dan's been there, with no relief of the major problem.
But we're way past points of interest. Jim is right. Bike mechanics are only interesting up to the point where they interfere with your riding. The latest videos, of the bike in the designer's fit-out and permitted trim when Dan bought it, show that it would be suicidal for Dan to tour with that bike where he wants to tour. That bike isn't fit to ride around the block.
The likelihood, after comprehensive and exhaustive (not to mention exhausting!) testing, is that, by a thorough process of elimination, Jags is right. Dan's particular Thorn Sherpa is faulty in some respect.
Thorn should either give Dan his money back, and apologise for his wasted time and further expense, or give him a new bike. Considering that the designer's parameters for the bike changed since Dan ordered his example, any replacement should be capable of doing what Dan wants.
Dan has been exceedingly patient and courteous, and done a great deal of unpaid testing; this thread is a masterclass in development testing. I can't say that I would have been as patient, or courteous, or done any of the necessary work free of charge; in fact, I suspect that most of us wouldn't. Congratulations to all concerned for being so civilised.
Andre Jute
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as we say in this part of the world jwestland small jockys big wips ;)
in this case size has nothing to do with the fact the frame is useless.
you can use all the tech jargon you want its faulty.
how come no other sherpa owners complained about shimmi, sherpa owners of all sizesas hobbes just said Dan tested this bike to the full and still it shimmie's.
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Jags,
As I mentioned previously near the beginning of this thread,
I get some shimmy on my Sherpa when I have panniers on (front and back). It starts at 20mph and eases off again around 25mph, it's not severe and dampens out with a knee against the top tube. Seems to vary depending on the load in my front panniers which are fairly big (older style Altura Orkney model) and probably sometimes a bit overloaded as the right hand one is my food pannier.
But clearly Dan's shimmy is worse than anything that I get and needs to be resolved.
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Dan
I'm quite shocked by your videos - I've never seen anything like it before (but then I've led a sheltered life). I do hope you get this sorted soon.
Ian
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+1
I would not be riding that bike with any sort of confidence. Have you posted these videos to Robin Thorn?
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Hi All,
I am very pleased to announce my Sherpa's shimmy problem has been resolved, thanks to Robin Thorn, Andy Blance, and Thorn the company. On learning more about the nature of the problem they shipped at their expense a replacement fork and Thorn EX rear rack to try, in hopes they would address the shimmy problem. I tried yet another tire change, and after these efforts, Thorn generously offered me a choice of solutions.
I have chosen their offer of a replacement bicycle in the form of a Nomad Mk2 with Rohloff. They have generously offered to build the basic bike to similar spec free of charge and with urgency, and will even take care to send it clearly labeled as a warranty replacement in hopes it will help with Customs duties.
Best of all -- and very reassuring to me -- they will take the extra step before packing of having Andy personally test it with the maximum luggage allowance as stated, so I can be truly reassured it is sound and fit for duty in field conditions.
Once it arrives, I will pack the Sherpa in the box for return so they can examine it to better understand what is wrong. I'm keen to find out, too, and very much hope something will be revealed. Perhaps, as can happen with any product, there was some unseen flaw in construction or materials that caused the problem. I've never experienced or heard of anything like it, so it is a rare event and an anomaly.
Robin topped his efforts with a thanks for my patience and an apology for inconvenience, and the result is both outstanding and very much appreciated.
Thank you, Robin Thorn and Andy Blance.
I am looking forward to working with Andy to spec the build and to receiving the bike. I will, of course, be starting a new Gallery entry titled, "Danneaux's Nomad" so you can follow my personalization of the bike and our travels together. Adventure awaits!
Thanks very much to each of you who have followed and weighed in with your helpful suggestions and opinions. It is a wonderful example of how a Forum can bring collective expertise to bear on problems greater than ourselves and build a sense of community in the process. I'm grateful for your help!
All the best,
Dan
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WoW that's fantastic news Dan .
well done Thorn outstanding service .
really look forward to seening the nomad special ,and a rohloff hub wow dan this is going to be a dream machine.
dan i really think you were the unluckest thorn owner on the planet, but these things happen the frame has to be faulty and it would be interesting to see if andy blance can figure exactly what went wrong .
are the frames put together in asia maybe it was a tea break frame ;)
anyway well done thorn on replacing the bike it was the right thing to do. DAN enjoy ;)
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Great to hear about the top notch response from the Thorn crew! And I hope it solves the problem perfectly.... not least, because it's a Nomad MkII that I ride! I will be especially fascinated to hear how you find the Nomad versus the Sherpa, Dan. Not too many folks get to compare them, especially with the rigorous testing you put the bikes through!
This shimmy business is fascinating. I am thinking about ways to explore it more. One idea I have is to somehow mount a vertical pole on the bike, like maybe a pair of 1x4 fixed on the sides of the rear rack and then bolted together up high, with some line stretch from the top to the front and back of the rack, so the whole arrangement is decently stable and rigid. Then put some small weight up there like 8 feet high, maybe five pounds. This should really screw up the way the bike corners. With enough weight up high enough, surely the handling of the bike could be destroyed utterly. How do things start to fall apart on the way to that utter doom?
Yeah, that is one of my long time engineering practices, to break things!
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That's really good news.
ian
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Superb news, Dan. Despite your travails with what can only be a rogue Sherpa -- a problem that can strike any manufacturer -- this outcome fully justifies your decision to order from Thorn in the first instance. Congratulations too to Thorn for find a Solomonic solution to what seemed only days ago to be an insuperable problem.
Also glad to hear you'll be joining the Rohloff elite...
Andre Jute
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Wow!Whoa!...woe.....WAHEY!
Top marks to Thorn for biting the bullet and top marks to Dan for patience and thoroughness.
The proverbial happy ending I hope.
Ian
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Great news Dan, that you have a resolution. You will not be disappointed with the Nomad I reckon.
But I'm intrigued by your Sherpa problems. Was this the first time you tried to tour with it fully loaded? If you'd done other tours surely the shimmy would have been apparent then.
And you're still on leave? What are you planning to do with the rest of your leave? It's a bit of a loss to miss out on the tour you'd planned.
Great delights await you anyway. Discovering the features and secrets of a new bike is always wonderful. Have a great time with the Nomad.
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It's good to hear, that your getting a replacement bike from the team @ Thorn (good work guy's)
I have new part's and wheels sitting about my home, just waiting on my new Thorn Nomad MK2.
Looking forward to some hard touring in NZ and the World.
Pete
;)
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Dan,
wonderful news about the replacement bike.
Welcome (in advance) to the world of Rohloff!
Julian.
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Great news and great service from Thorn!
I hope we get an update on what was wrong, quite curious now...could just have been a dodgy weld, it happens, no manufacturing process can be 100% perfect, or a rough shipper (don't get me started in couriers, the amount of stuff they broke due to rough handling in a technical support job I worked at was unreal....)
JimK you're not getting anywhere near my bikes! ;)
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Fantastic news Dan, and all at Thorn have excelled themselves here ... )thinking we should look into nominating them for some sort of customer service award, if such a thing were possible online).
I can't wait to see pics of the new machine, and also your impressions of Rohloff ... so much to look forward to ... happy days indeed. ;D
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Hi Dan et al,
I've been following this thread with some interest and it's good to see the happy outcome.
I must see if I can induce a shimmy in my Club Tour........ ;)
Cheers,
pj
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Danneaux, didn't you sat in your first post that,
"This is essentially what happened to my Miyata 1000LT *after* my Great Basin tour in 2010,"? Did that bike develop a shimmy as well? I'm intrigued. Also, are Thorn paying the extra cost of the higher spec Nomad, or are you paying the difference? If the former, I do think I feel a shimmy developing in my steed.....
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the sherpa has bigger tubes better spec thats the reason he changed his bike in the first place if i'm not mistaken. ::)
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why don't you let the man answer himself? Legions have traversed the globe on his former model of steed. I am trying to ascertain if there is a common denominator to his shimmy problem.
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hold onto your wig there bucko no need to loose it ;)
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"This is essentially what happened to my Miyata 1000LT *after* my Great Basin tour in 2010,"? Did that bike develop a shimmy as well? I'm intrigued.
Hi Joe,
My timezone is offset from most on the list by about 8 hours so there can be a little delay before I see or respond to a topic if I'm asleep. :D
My quoted statement meant the Miyata also developed a shimmy whose origin I could not definitively pinpoint, but it manifested differently and was almost certainly the result of crash damage, which was not a factor in Sherpa's case. The Miyata and I took four very hard falls that tour (including one that put me through a cattle-guard, ouch). The Miyata was fine before the trip, fine during, not-fine after (the last fall was just before the trip concluded, and came when I was blown off the road and down an embankment by a fuel tanker taking evasive action to avoid an oncoming car that passed in a no-passing zone. He needed the road shoulder more than I did). I have not stripped it to check, but I suspect the fork or rearframe (rear triangle) or both may have been tweaked, since I was fully-loaded in each fall (I'd not fallen in over 20 years, then hit the jackpot on that trip).
The difference between the Miyata and the Sherpa is the Sherpa has never fallen, either while parked or while being ridden. Also, the Miyata shimmied at all speeds and all loads "after" the trip was concluded, and the Sherpa did in correlation with a rear-based load (Sherpa handled front loads fine, front-and-mid loads fine, then declined with a rear load of any sort, degrading further with added weight, up to and at a normal touring load). The bikes also differed in geometry, design, materials, and the racks used, and there were normal variations in load and placement as well.
So, no common denominator I can see.
Jags is correct; when I selected the Sherpa to replace the Miyata, I chose it deliberately because it had larger-diameter tubing more likely to better handle a touring load. The Miyata used proprietary splined triple-butted tubing that did a manful job, but it was still of standard road-bike diameter. By any standard, a bike made with larger-diameter tubing should perform better, and Sherpa was selected specifially for expedition touring.Legions have traversed the globe on his former model of steed
Absolutely! The Sherpa has been used with great success by many and I have never run across a similar reported problem. That's why I am convinced mine was an isolated anomaly as can happen with any production product, and is not in any way typical of the breed. Though I could not locate or address the cause even after extensive documented testing, there is some reason for this very atypical behavior and outcome. Thorn will be examining the frame in due course, and I am hoping very much they can identify the cause, though if it is internal (perhaps a flaw in the tubing or a weld that is internally incomplete or not of full depth and therefore invisible), we may never know.
Thorn have done an outstanding job responding to the problem, and the seriousness with which they are approaching it is reassuring to all.
Best,
Dan.
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Dan, I do not believe you ever sleep ;)
Ian
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I suspect the fork or rearframe (rear triangle) or both may have been tweaked,
This "tweaking" business gets into some really deep mysteries, how metals change properties through mechanical stress, corrosion, etc. A big smash-up can surely crack a frame. There must be some sort of relationship between how much of a load one is carrying and how big a bump one needs to hit before the frame falls apart. But there must be subtler ways a frame can weaken, short of cracking up.
No doubt, airline manufactures work through a lot of this. I fear that there just isn't enough money in bicycles to make it worth smashing up a few dozen to get the limits properly characterized!
We've got a ride planned here for tomorrow, to ride down to New Paltz and haul back the first semester's college textbooks, me and my girlfriend's teenage son. That ought to give us some nice loads to test our bikes!
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Dan, I do not believe you ever sleep
Not much, Ian, not much. ;D...haul back the first semester's college textbooks, me and my girlfriend's teenage son. That ought to give us some nice loads to test our bikes
I'll say, Jim! Do be careful; if those texts weigh as much as some of mine did, it'll be a load indeed, so watch your back on the un/loading. When you think of paper as compressed sheets of wood, well, the weight makes sense.
I agree; metal fatigue and changes in perceived ride quality are fascinating topics.
For years in the racing community, riders thought their frames "went soft" after a hard season of racing*. I believe I remember some tests and articles (Velo-News?) from the late-1970s that disproved this. Metallurgy and materials science argues against it, but riders were convinced. How much was the placebo effect, and how much was real? Back in the days of cotton hadlebar tape, team mechanics labored through the night to replace it for each following day. Riders always reported feeling a "boost" from what felt like a fresh start each day.
Fascinating stuff, unless it is happening to oneself, in which case it is as horrifying as it is fascinating.
All the best,
Dan. (*who knew some folks back in the day who got really good deals on team closeouts of wonderful frames at season's end)
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JimK wrote...
This "tweaking" business gets into some really deep mysteries, how metals change properties through mechanical stress, corrosion, etc...No doubt, airline manufactures work through a lot of this.
Jim, I have a film to recommend for you, based on just this plot:
http://en.wikipedia.org/wiki/No_Highway_in_the_Sky
...and...
http://www.aycyas.com/nohighwayinthesky.htm
It is available on video, and the trailer for it is here:
http://www.youtube.com/watch?v=Jn9gvBYKSkc
Best,
Dan.
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Of course there was always the Comet disasters (http://www.youtube.com/watch?v=_3JZ3wHlgvI). But with aviation metallurgy we are talking about a quantum leap in stress forces and repetitive cycling compared to a bike frame.
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This "tweaking" business gets into some really deep mysteries, how metals change properties through mechanical stress, corrosion, etc. A big smash-up can surely crack a frame. There must be some sort of relationship between how much of a load one is carrying and how big a bump one needs to hit before the frame falls apart. But there must be subtler ways a frame can weaken, short of cracking up.
No doubt, airline manufactures work through a lot of this. I fear that there just isn't enough money in bicycles to make it worth smashing up a few dozen to get the limits properly characterized!
My Utopia Kranich, a bike with a track record going back to 1936, is thoroughly tested by an independent laboratory run by Ernst Bruch. At first I thought this was because they redesigned the frame with special lightweight double-butted custom-made Columbus tubes, but in fact it is because these particular Germans who built my bike are obsessives. They test everything. Unfortunately their latest Radgeber (Advisor magazine, current one No. 17) at http://www.utopia-velo.de/relaunch/RRG_content.a4d?seq=R001048 concentrates on showing the test of the Big Bull rims with the electric motor, but in earlier issues they published photographs of the frame under test. Here are some images screen dumped from the earlier Ratgeber No. 16 of February 2011.
(http://www.coolmainpress.com/miscimage/Utopia%20photo%20of%20Ernst%20Bruch.tiff)(http://www.coolmainpress.com/miscimage/Utopia Kranich under test 1.tiff)(http://www.coolmainpress.com/miscimage/Utopia Kranich under test 2.tiff)
From the left: Ernst Bruch, boss of the independent laboratory; I'm not letting him near my bike again! Fitted-up Utopia Kranich under test. Utopia Kranich bare frame under load. (BTW, I hadn't noticed before that I loom over Herr Bruch's shoulder, protecting my bike against testing to destruction!)
But, before you (not addressing you, Jim, I mean everyone) start demanding that Robin Thorn lash out for such tests, be fully aware that this sort of probably unnecessary tests adds to the cost of the bike, probably in the case of a small maker like Thorn by about £1500-3000 per bike.
***
Note the words "probably unnecessary". My bike is actually much lighter than it looks; in standard ex-factory trim, it is about 5kg lighter than a Gazelle stadssportief (commuter with touring/sporting pretensions like my Gazelle Toulouse) with a Nexus 8 speed hub gearbox, or a Trek Benelux equivalent. So the testing may have been necessary either to determine the 170kg total load rating, or to ensure it as a design target. I don't mind paying for it because I'm an obsessive myself, and the sort of German who buys the Utopia top models is clearly middle-aged and comfortably off; they like owning a bike made by obsessives without regard for cost, and don't care what it costs, as long as it doesn't break. Thorn is in a different market, and is famous as a value for money bike. That's an image that no one, least of all the customers, want to disturb lightly....
But, in general, bikes, and especially steel bikes, have evolved to a very high stage of development in over a century of continuous improvement by experience. Testing won't reveal anything much, and offer only marginal improvements, unless you want to push the boundaries, most often by going to stupid-thin tubes. (Or you might consider guaranteeing the Kranich frame for ten years with a 170kg load rating an excessive ambition, but I'm still not sure all the testing is actually warranted on a cost-return or an opportunity-cost basis. That it is justified by the reaction of the customers is an entirely different matter.)
***
I wouldn't bet against you if you said Thorn won't find anything visibly wrong with Dan's Sherpa when they cut it open across a joint. I think it by far most likely that some part of the rear of the bike was overheated in the welding, and not properly stress-relieved, that it is therefore harder-responding than the rest of the steel around it, and thus causes an oscillation. (Dan's jokey remark about racing bike tubes going soft in hard use is exactly the opposite!) My second bet, second by several lengths, is inadequate weld penetration. My third bet is a wrong tube length, so that the butt was cut off and the weld is in the thin part of the tube, and my suspect is the seat tube rear end, or one of the tubes joining there; that could conceivably create a micro-wriggle when the rear of the bike is loaded which by the time it reaches the front wheel could cause a nasty shimmy, but at the seat end would be invisible to the naked eye.
Put your money on here.
Andre Jute
Bikes I mention are illustrated at http://coolmainpress.com/BICYCLING.html
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Andre did you ever think of writing a detective novel ;) you and Dan would make a great team ;D
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Andre did you ever think of writing a detective novel ;) you and Dan would make a great team ;D
Sure thing, Jags. CoolMain will be publishing a detective novel called EIGHT DAYS IN WASHINGTON in a couple of weeks. http://coolmainpress.com/home.html -- Andre Jute
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Nice one Andre i walked into that ::)
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Put your money on here.
Done. I'm betting on exactly one of the variety of factors you describe, Andre. Couldn't have put it better myself, and the scenarios you describe are about all that's left, given there's no flaws visible. Very nicely outlined and described and one of those flukey things one cannot really expect.
All the best,
Dan. (hat-tip to Andre)
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Dan,
I'm glad to hear that you're getting a replacement bicycle! I haven't been keeping up with your trials and tribulations recently as I've had some myself on the computer front.
I've got lots of reading to catch up on the forum and started by reading through this thread.
I'm interested to know what size frame you've settled on for the Nomad replacing your Sherpa, is it going to be the 590M, I hope you manage to get a good fit as when we talked about it before, you thought that your Sherpa was a better fit than the new range of Nomads would allow for your needs, but thought that the 590M would be the closest to the fit that you like.
It does open up scope for many future theads, the Nomad build, shake downs, thoughts on the Rohloff hub, etc etc. I'm looking forward to much more good reading!
All the best,
Iain.
:)
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Hi Iain!
Welcome back; sorry to hear you've had computer woes. They never go down at a good time, do they?
To answer your question directly, I am going with the 590M. To see the reasons, read on...
Sizing was one of the things I was not sure about, because the Nomad Mk2 has different geometry from the Sherpa Mk2, so I asked Andy, who kindly weighed in with suggestions and guidance.
Really, it was a matter of first going for a size that fit best given my selection of handlebars, then looking at which frame would give me the greatest cargo capacity and the most stability. As the brochure says, most people could ride two sizes of Nomad, and the choice depends on handlebars and whether one would use a sus fork or not. That gave me four possibilities:
565M = greatest weight capacity, a bit small, usable with drops
565L = lower weight capacity, better stability due to longer front-center, no drops
590M = 2nd highest weight capacity of the 4 choices, longest virtual TT I can use with drops, requires shorter stem
590L = greatest stability due to longest front-center, but lowest max weight rating, no possibility for drops
It is extremely unlikely I will ever run a suspension fork, so there is no need to allow for that. For the kinds of riding I do and where I go the softer ride would be nice, but I cannot accommodate the greater maintenance schedule of a sus fork, and it would also limit my pannier options (perhaps to only a Tubus Swing font rack; otherwise, HB bag and rear panniers only). If I need more suspension, then a change in tire pressure or section width/profile would be a better choice for me. A rigid fork also provides fixed geometry, and will eliminate a host of handling variables that would be present in a sus fork because of its range of travel and as a result of wear.
I agonized (truly!) over handlebar choice. I've always used drops, and now pretty much have to, thanks to a series of past injuries, including the long-ago car accident that started me cycling "with intent" while in high school. The capper was falling out of a hot-air balloon that was in pullout and catching myself on the way out (Didn't let go! Not for nothin'!!! :o). I find I need to ride in a position where my palms face each other or nearly so. I really thought I might be able to adapt to straght 'bars by using bar-ends to achieve an on-hoods position and gave it serious consideration.
To make sure, I needed to try some 5° 'bars and 'ends in my likely size, so I asked my same-size neighbor if I could try holding the ones on his MTB, and...it just didn't work for me. I discovered the bar-ends put my hands far wider than my usual 44cm drops' brake hoods, and I had no braking available while on the 'ends. When I moved in to get the brakes, my ex-hyperextended/hyperflexed wrists bent sideways, my tendonitis-y elbows went akimbo, and the old rotator cuff/shoulder separations yelled at me. I could manage briefly, but not for sustained riding. I remembered Tektro once offered an adapter that clamped onto the ends of brake levers to offer access from bar-ends, but a call to Tektro showed it was discontinued some time ago and is not even available through eBay (they came OEM on some pedalecs). Even if I could put my brake levers very close together with a narrow straight-bar option, I would have been too-wide on the 'ends where I would spend most of my time. So, drops it is. They just don't hurt. I really do use the drops when plowing into headwinds; otherwise yes, most of my time is spent atop the brake hoods. On the Folder I am building, I am going with a short-reach variation on bullhorn/pursuit 'bars that duplicate the tops and brake hoods position of my present drops sans hooks (makes a smaller fold, same 44cm width with reversed interrupter v-brake levers where the hoods would be). That is a possibility to consider in future for the Nomad, but the drops are a do-all solution for me with many more hand positions to alleviate fatigue.
So, no sus-fork meant I could go "bigger" and the drops meant I had to go "shorter", so a 590M it is. It is a compromise in the fewest ways, an advantage in most, and looks like the spot-on fit for me with drops if the stem reach is shortened. The rated maximum weight capacity is the second-highest (missing first by a small margin) and much higher than the 590L. The 590M Nomad's front-center measurement (using the virtual top tube as a proxy) is 35mm greater than my Sherpa Mk2, and the chainstays are longer, which should result in weight further within the bicycle's wheelbase, also for greater stability.
To make up for the longer top tube, I will need to drop some stem length, but the 80mm stem is the same as I use successfully on my tandem and three other touring bikes with similar-length top tubes. I am hoping a happy side benefit of the shorter stem will be less of my weight over the front hub, which is bound to help stability as well. It is generally accepted a handlebar bag should be lightly loaded because it carries weight high and forward. Well, what about the rider, who is heavier? It can only help having more of my hand-contact weight further within the bicycle's wheelbase.
If I get old someday, the shorter top tube allows for some adjustment to a more upright position using arc, H, or comfort 'bars to get my palms more parallel. I've asked the steerer remain uncut so I can best determine where to place the 'bars vertically (and can determine how best to package the Tout Terrain The Plug 2 and Power Amplification Technology booster cable). I have found long ago the "right" position for me is to have the tops of my drop handlebars at the same height as my saddle-top. My preferred position on the bike is with a 45° back and 45° arms when on the brake hoods (see pics). Doing so puts about equal weight on my hands and seat and puts my head/neck in a good position and has worked well on 300-400km day rides. This comes closest to the model picture labeled "Fairly Relaxed" in Thorn's very helpful new sizing guide, available here: http://www.sjscycles.com/thornpdf/SetUpHiRes.pdf
Mid-tube standover on the Nomad with 2.0" tires is the same as on my 560S Sherpa Mk2 with 1.75" tires, so I will have adequate standover even on damp desert playa and on goat-tracks. In fact, I could even go up one tire size on the Nomad and still equal the Sherpa's standover.
I have decided to pass on getting the newer Berthoud shifter in favor of mounting the standard Rohloff shifter on a 50mm T-bar under the stem on the right side. For a brief change of position and some trail/single-track use, I want to be able to mount and use my 'cross-top interrupter levers, and the Berthoud took up too much room for that (I could have gone with a single interrupter lever on the left side only). The T-bar placement is simple and about the same reach from the brake hoods as I currently have to a bar-end shifter. It also allows me to change handlebars at a later date and leave the Rohloff shifter and cabling undisturbed. I have downtube shifters on some of my other bikes, and the reach to the T-bar isn't as far, so hopefully it will be fine. If my choice proves disastrous, I could someday purchase a Berthoud and put it right.
The net result of choosing the 590M with a shorter stem and drop 'bars is my position should be very close or identical to what it was on the 560S Mark2 Sherpa, with the added benefit of greater cargo capacity and a longer front-center for stability.
Robin and Andy's response since getting involved has been outstanding, and they have worked as a team with me to define and refine and address my needs. They have both been in contact by email every single business day without fail, and all parties are copied so we are all on the same page. Their reponse has been phenomenal and is reassuring to us all. They have taken this problem very seriously indeed, and have worked very hard to address it. My sincere thanks to them.
Thanks for your kind words, Iain; I'm also looking forward to the Adventure ahead!
All the best,
Dan.
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Some of the people who write blithely and ignorantly on the net about bike fit should read Dan's post above, and Andy Blance's brochure, and smarten up their information base.
Can't be more than handful of bike-makers on the planet who can offer one chap of fixed size four bikes that will all fit him, each with a proper technical rationale.
What an amazing advertisement for their wares the people at Thorn have turned one rogue Sherpa into!
Andre Jute
Sometime creator of multinational household brands
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It's funny people bitching over sizing, whereas most bikes you are lucky if you get 5 sizes of them, with no choice of top tube length ;D
565M = greatest weight capacity, a bit small, usable with drops
565L = lower weight capacity, better stability due to longer front-center, no drops
590M = 2nd highest weight capacity of the 4 choices, longest virtual TT I can use with drops, requires shorter stem
590L = greatest stability due to longest front-center, but lowest max weight rating, no possibility for drops
###(newbie question...)
So, am I correct in thinking that longer top tube equals less weight carrying capacity compared to a frame of similar size with short top tube?
Due to more flex?
To make up for the longer top tube, I will need to drop some stem length, but the 80mm stem is the same as I use successfully on my tandem and three other touring bikes with similar-length top tubes.
###I had to do this for my XTC, so far no problems.
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most bikes you are lucky if you get 5 sizes of them, with no choice of top tube length
That's right! On some of my other bikes from the 1980s, only three or four sizes were offered across the entire line with only a single example that might have fit (i.e. 21", 23", 25" by c-t seat tube length...). Worse, these were often made "square", meaning they had identical geometry and top tube lengths to reduce production costs. "Sizes" meant the seat tubes and head tubes were simply cut longer or shorter to adjust standover. Stem sizing was the order of the day, especially if one was not fortunate enough to require the middle size, as I did. Everyone was the same distance behind the bottom bracket and (unless stem reach was adjusted) smaller people had a long reach to the 'bars and big people were cramped.
Also --just as you say -- no choice in top tube length. My sister had to deal with this. She is about your size, and she wanted a really nice mixte in the mid-'80s. Since all the offerings by her preferred maker had the same "square" geometry (only the virtual TT height differed), she was actually better off with the "21-inch" than the 19 because the larger frame was the same but put the handlebars a bit higher (and, thanks to the head tube angle, a bit closer as well, though it required a special quill stem with a 50mm reach). To get a reasonable seat tube angle, I had to use an SR MTB seatpost with a sliding track. The fit wound up perfect, but it took some real compensation to get it. And, that was the best sizing offered at the time. What is really nice here is once I settled on HB choice, I could hone in on other factors like getting the best fit (most important) and weight rating (also very important in my case). None of this would have been possible (or I would have had to be "lucky") with fewer offerings.
This is why some people "back in the day" could only get a decent fit by going for a custom frame. Compared to the "old days" of custom frames, Thorn's offerings are wide-ranging enough to comprise a near-custom fit. As close as can be without being truly bespoke.
am I correct in thinking that longer top tube equals less weight carrying capacity compared to a frame of similar size with short top tube? Due to more flex?
Spot-on, Jawine; that's exactly right.
For the same diameter, a longer tube will have more flex over its entire length than a shorter one. The opposite is also true; for a given diameter, a shorter tube will be stiffer over its length and more resistant to flex.
I had to do this for my XTC, so far no problems.
Good news! I am also fortunate to have had such good experience at the same 80mm length, so things bode well for a great outcome. I do have the option to change to a different 'bar at some point, and by leaving the steerer long, I have some height adjustment also. Once I see it and sit on it, I will have a much better idea. From all I can see, it will duplicate the Sherpa's fit as nearly as possible. It appears the 'bars will "float in air" at the same place as before, differing only in how they get there.
Best,
Dan.
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I still suspect my XTC was build for a much taller person (525L, 170mm cranks, I clear top tube by just an inch and an half) but where's a will... :D
So my other bikes also have a 55 cm top tube but...bar that slope back (roadster, moustache) make for a lot less reach than the traditional top bar. One comes in just two sizes (roadster, 700C) the other one comes in 5 sizes.
My parents bought Koga Miyata Signature, with Rohloff (so going to want to try one during Christmas for the Rohloff) not sure how many sizes they do. But they have butterfly bars and geometry similar to Dutch roadsters.
Luckily I didn't have as much hassle as your sister! :)
It's very hard to find short reach vintage parts, generally only mountainbike/bmx stems have short reach. That puts a lot of vintage bikes out of my reach, bar some very common road bikes made for shorter men ;) (but then you can FORGET about a vintage 38cm bar again)
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Thorn posted a couple videos with some commentary on their facebook page:
https://www.facebook.com/Touringbikes
They loaded a Nomad with 43 kg and took it on a high speed descent to check for any shimmy or wobble - which they did not find! .. ah, the first run had 65 kg of load!
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Hi All!
Thorn (The Company, Robin himself, and Andy the designer) have been pulling all stops to make sure my isolated shimmy problem was just that -- an isolated incident. They have really outdone themselves and have made the greatest possible effort all-'round, and have been in contact with me by email nearly every business day to advise, to update, and to include me in the process of equipping the new bike to best suit my needs.
Really, their efforts have been outstanding and beyond, and I am terrifically pleased!
The most recent effort has been to videotape and post footage of my new Nomad under test by Andy himself to thoroughly wring it out while carrying the same weight in similar conditions to what I will need to haul on occasion (as added benefit, Andy and I are nearly identical in height and weight). Robin has just passed the link from their Facebook page on to me, and has authorized me to share it with you. Here, go see for yourselves how the new bike handles under load, on downhill bumpy lanes with Andy at the helm at high speed (45mph/72kph): http://www.facebook.com/Touringbikes
Andy did the riding, Robin drove the van, and Cath Colenso did the video -- a real team effort.
I can't begin to tell you how heartened I am by their efforts and the results. It is the close of the business day for Thorn, but I will write and ask Andy if I may reproduce his last email verbatim, detailing his efforts and load strategy so we may all learn from it. If that is not possible, then I will summarize it instead. Thorn have done an incredible job in addressing a completely unanticipated and unexpected problem with one of their bikes, and it is so reassuring to find they have taken it so very seriously and have stood squarely behind their product. This is something we can all take reassurance in, and is very heartening indeed.
My sincere thanks to Robin, Andy, Cath Colenso, and all the team at Thorn Bicycles.
All the best,
Dan.
Well done! Well done, indeed!
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Andy and I are nearly identical in height and weight
Now that is what I call thorough above and beyond!
Certainly makes me happy that I picked such an exemplary producer for the bike I bought!
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Now that is what I call thorough above and beyond! Certainly makes me happy that I picked such an exemplary producer for the bike I bought!
Boy! I'll say!
You know...it is one thing to go carving downhill like that oneself, and something else altogether seeing someone else do it. I was genuinely concerned for Andy when he and Robin first proposed the fully-loaded road test. As hungry as I was for the data and results, just as much I didn't want Andy to get hurt.
I held my breath with all sphincters squinched when I saw those videos (even larger on the YouTube verson linked off the Thorn Facebook page). What if Andy meets a ca-- oh! There's one now! Neeeeeeeeowwwwwwwwwwwww! and it was past...and (from my perspective), on the wrong side of the road!!! And, don't forget, for Andy the brakes really were setup for the wrong-side of his road! And also drop handlebars, which are not his preference or what he is most recently used to.
I think he did a really outstanding job and was very brave indeed to give it a go. I am over the moon with joy, and very happy and relieved he came out safely as well.
Best,
Dan.
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No hands at 45mph. Don't do this at home, kids.
That is a truly impressive pair of videos, in any bicycling terms, but in this thread especially for what they represent in customer and product care and exceptional service.
Andre Jute
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on the wrong side of the road!!!
Yeah, my heart skipped a beat at that point in the video, the first car. Crazy!
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great bit of bike control ,they sure pulled out all the stops for this bike.
dan at last your going to ride one of the best touring bikes on the planet ;)
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mind you i hit 52mph on a decent in the uk somwhere in the cotswolds but i didn't let the bars go ::)
just shows how solid this bike is, my sherpa rides like a dream loaded and unloaded.
yeah great company Thorn not to many people would go to this trouble to satisfy a customer thats for certain..
bet everyone on the forum is chuffed they own a thorn bike ;D ;D ;D
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Hi All!
Andy kindly gave permission to post his email to me verbatim, detailing his testing strategy for the Nomad and detailing how much he carried on his test runs as well as how it was arranged. I found his packing scheme to be very useful. I have converted it to graphic form to keep in my handlebar bag for reference so I can duplicate his success on those occasions when I must carry a maximum load. I'll post that graphic later, but for now, I think Andy's description says it best in the man's own words...
Hi Dan,
How are you?
I have just come back from testing your Nomad Mk2 590M.
Robin drove the van behind me, whilst Cath took some video footage.
I let the bike roll down a moderately tricky and fairly bumpy descent, at various speeds.
I had 63.25Kg of load in total, including the actual bags themselves, this comprised of:-
3Kg in the bar bag.
10Kg in each front pannier.
2.5Kg in the 3 bottle cages.
7.75Kg mounted transversely in 2 dry bags, on the top of the rear carrier.
And 15Kg in each rear pannier.
This is more than I’d like to cycle with! And certainly more load than I’d wish to control with 44cm drop bars!
However, the bike behaved itself and I reached 42 miles per hour. As you will be able to see, when Robin sends you the link to the video, I was able to ride the bike “no hands” with my arms out like wings. I was able to tap the bars to promote a wobble and the bike corrected itself almost instantly. If I ever needed to carry a huge quantity of water, I’d feel confident that I could control the machine with an even greater load…it certainly wouldn’t be my idea of a fun day out though!
We also took footage of my second run, this time with the amount of luggage that I say the Nomad is nice to pedal with…”just” 10Kg at the front and we removed 10Kg from the rear panniers…so 43.25Kg in total.
You can see me cornering quite hard and deliberately hitting bumps without my hands on the bars. I also hit the bars fairly hard several times, whilst riding no hands in excess of 44mph and I also shook the bike…try as I may, there was no way that I could make the bike wobble. It handled superbly and it would have been great fun to carve some lines out of a technical hairpin descent.
I must admit to having been slightly nervous but now I have a warm glow of pride…I’m sure you’ll be very pleased with the way this machine behaves…we should be able to send it off tomorrow and I will make certain that it is very well packaged!
Best regards,
Andy B.
Andy Blance
Designer
Thorn Cycles Ltd
Andy the Designer has occasionally been referred to as "Andy the Test Pilot" and that surely held true in his load-testing my Nomad; what a nice job he did for all of us! The load figures and placement should come in really handy whenever large loads are to be carried, as these are proven-in-practice.
Best,
Dan.
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My n-1 bike is a Workcycles Super-Transport which is a very sturdy bike and capable of handing large loads. But it has Nexus-8 IGH and roller brakes, neither of which work in the mountains. So bike n is the Nomad. I didn't get it so much for touring as for long distance utility. Traveling with a purpose, and as often as not with a load. All my experience with it so far has confirmed that I made a good choice.
This report is really wonderful capstone. Well earned pride, Mr. Blance!
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Hi All!
Here are the loads and placements Andy Blance used in testing my Nomad. I used his metric (Kg) figures directly, and then rounded the poundage conversions to the nearest whole pound in each case. Because of that, the pounds won't exactly equal the kilograms if you add up the totals. Go with Andy's figures in Kg as most accurate to avoid rounding errors.
Since I find it helps to visualize things graphically, I made these little diagrams to carry in my handlebar bag so I can match Andy's loading scheme when I must carry greater weights (i.e. during my actual desert crossings, when I must carry extra weight in water and food to sustain me).
Please note the difference in weights and placement for the two schemes ("Maximum" and "Nice to pedal").
Best,
Dan.
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Wow thats brilliant Dan no idea how you do these things but that a fantastic way to show how to load your bike.
mind you i will never carry that kinda weight, i know you need it for your type of touring but i'll stick to plan b tarmac all the way nice and light. ;)
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i will never carry that kinda weight, i know you need it for your type of touring but i'll stick to plan b tarmac all the way nice and light. ;)
My credit card weighs 30 grams and the fellow in the sag wagon doesn't mind carrying it for me!
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;D ;D ;D way to go Andre.
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My credit card weighs 30 grams and the fellow in the sag wagon doesn't mind carrying it for me!
That would be the Titanium card, right? The Silver, Gold, and Platinum cards are simply too heavy! :D
Best,
Dan.
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Hi All!
Thorn Cycles' designer, Andy Blance, has expanded on his earlier views with some load schemes and suggested weights for touring – this time for typical European and Alpine touring with less than the Nomad's maximum capacity. He has kindly given his consent to share his comments for the benefit of the Forum.
Since loads – and how they are packed – directly affect a bike's stability, I think it is helpful to include his recommendations in this same thread. Unlike my more specialized requirements, the greater number of cyclists will likely tour with lesser loads, just as I do when in more populated areas. When I toured Europe for 5 weeks, I carried 25kg...there was simply no need to carry such enormous back-stocks of food and water I require in the wilderness.
Hi Dan,
Thanks for your email. Fiona and I are more than happy for you to publish our recommendations for loading bikes for touring in Europe, where supplies and services can usually be found every day.
Like you, we really enjoy many different types of cycle touring. We especially like to be at altitude in wilderness and we certainly agree that it is the quantities of food and water which are necessary that produces such extreme loads! The bonus is that these loads reduce…often on an hourly basis!
...I know when Fi and I go cycle camping in Europe, we very occasionally carry as much as 32.5Kg.
We carry either a bar bag or a saddle bag depending upon the type of tour we are planning.
Bar bag set up…ideal for really long tours. Includes plenty of appropriate clothes for cultural activities.
We aim to carry as little as possible in our bar bags…phone, camera, binoculars, passport, glasses, wallet and bean bag for use as a camera support…this also line the bottom of the bag. Total 1.75Kg
We carry 2 x litre coke or sprite bottles of water in the seat tube and under down tube cages and 1 x 0.75l bottle of drink in the down tube cage Total 2.75Kg.
We carry alternative shoes some provisions and clothes we won’t use during the ride in the front bags. Total 6Kg
We use a large, transversely mounted dry bag with our share of the tent, air mattress and sleeping bags. Total 5Kg
Our rear panniers carry our share of heavier tools and spares, food, cooker, yet more clothes and hopefully, some wine! Total 17Kg
Grand total 32.5Kg
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Saddle bag set up…ideal for serious cycle tours in the Alps. Includes one set of lightweight smart casual clothes, to prevent us from feeling self-conscious, should we decide to stay at a hotel and go out for a meal.
We carry 2 x litre coke or sprite bottles of water in the seat tube and under down tube cages and 1 x 0.75l bottle of drink in the down tube cage Total 2.75Kg.
We carry alternative shoes some provisions and clothes we won’t use during the ride in the front bags. Total 4.25Kg
We use a large saddle bag with a warm layer, waterproofs, snacks, simple tools inc. tubes and a document bag with passport and extra cash .We have all the things we are likely to need for the day’s cycling in our saddlebags. We also carry phone, camera, binoculars, glasses and wallet in the pockets of the saddlebag. If we wish, we can leave all the other kit at a hotel or in the tent and go for a day ride, without having to extensively re-pack. Total 5Kg
Our rear panniers carry our share of heavier tools and spares, food, cooker, tent, sleeping mats, sleeping bags, yet more clothes inc. down jacket, which doubles as a pillow and hopefully, some wine! Total 14Kg
Grand total 26Kg. This is the set up you can see Fiona and me using in the Nomad brochure on pages 3 and 15. There is no need to carry too much food but we always carry a whole day’s rations in addition to what we plan to eat that day. When the bikes are set up like this, I believe that they will out handle any racing bike or mountain bike!
Best regards,
Andy B.
Something that really caught my eye as useful and appealing is Andy and Fiona's inclusion of clothing and footwear appropriate to off-bike use and for attending cultural events. If the bike is used for a "balanced holiday" of touring, one doesn't always wish to look like a cyclist off the bike! Touring is *supposed* to be fun; not all wish to Adventure Tour in the most extreme of climates and locales, and even for those who do, the variety of an occasional break in routine is welcome. And nearly everyone will agree...carrying less weight is a whole lot more fun. Besides, a bike designed to handle maximum loads provides an extra margin of security at something less than maximum carriage.
I (Dan) have made some graphics that show how Andy and Fiona distribute the two kinds of loads described above, and attached them below.
Best,
Dan.
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What a superb outcome! (See, I told you Thorn would see you right!) Thorn has fully justified your decision to buy the right bike for you even over the big ocean.
I look forward avidly to your reports of your Nomad in the other threads that will follow, Dan.
We should also take a moment to send a good thought to Robin Thorn and his shareholders, if any, for taking a financial hit by putting the customer first.
Congratulations to all parties on sorting the matter in a civilised, transparent manner -- and turning the whole into a major, truly useful, educational effort.
Andre Jute
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Dan - a great conclusion and service from the Thorn team! So glad it all worked out well. I knew there were many great reasons to buy a Thorn and this shows yet another when things, on rare occasions, go terribly wrong. Looking forward to more desert touring tales on the new Nomad! :)
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Fantastic news all round Dan very best of luck with the new bike.
will we be getting any photos of the nomad sure hope so.
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Hi All!
Thorn followed-up on their outstanding efforts and warranty response to my Sherpa's shimmy problem by having Andy do a complete test ride. Robin wrote me yesterday, saying...
"...Andy tested it last week:
http://www.youtube.com/watch?v=xNQzNKl8B6E&feature=plcp
I (like you) no doubt wasn't expecting this to be the result!"
I am as surprised at the result as Robin -- there isn't a single sign of shimmy during Andy's test-ride. Sadly the bike shimmied under me at even a jogging pace with half the load arranged identically -- also while coasting, sitting upright and hands-free like Andy.
Thorn's careful follow through and testing is further sign of their concern for the customer.
Shimmy remains a difficult problem to solve, much less grasp. In my research I have read of bikes that shimmied unusably under one rider and were then sold on to perfectly happy buyers who never had a problem. Similarly, bikes with no problem have developed shimmy with new riders of the same size and mass, and it appears every brand and geometry and size of bike can be affected if the right factors all come into play. The hard part is determining those factors and addressing them. My example is the only Thorn I have known to shimmy, a sign they have a much better handle on avoiding the problem than other makers.
Rivendell's Grant Petersen wrote a short summary of the issues related to shimmy and the difficulty in identifying and resolving the problem in Rivendell Reader 42 ("Early 2010"), reproduced here: http://www.rivbike.com/kb_results.asp?ID=80
Best,
Dan.
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This gets me thinking about bicycle black boxes. We already have such amazing tools for tracking physiology... heart rate monitors etc. I wonder what sorts of little mechanical gauges are available to measure e.g. strain at various points around the frame, the rotational position of the steering tube inside the head tube. What about the way the tire is supporting the rim.
One of my nephews has a tricky heart and sometimes they have him carry a little EKG unit around for a few days to try to catch whatever funny business is up at the time.
It doesn't take too much complexity in a system to open up enough territory and enough corners into which freaky behavior can tuck itself and hide. Sure frustrating though!
Did they run this test using your luggage racks? Ah, this is a mystery that is just going to stay a mystery, I fear!
Glad though that your Nomad is pulling through for you!
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...Did they run this test using your luggage racks?...
Hi Jim! Nope. I had been running the Surly Nice Rack (rear) on the Sherpa and I kept my (separately purchased) Throrn Low-Loader MkV pannier racks for use on the Nomad.
It is possible something there was amiss, but fitting the Thorn EXP rack to the rear of the Sherpa didn't help, and the same Low-Loader MkV racks on the Nomad has made no difference on it. While it is arguable I could try the Surly rear rack on the Nomad, I don't want to tempt fate! Andy Blance has done a very nice job designing the EXP rack and it works extremely well in practice, so I am inclined to leave well enough alone...even for physics!
Glad though that your Nomad is pulling through for you!
Thank you Jim; me too! The Sherpa was a lovely bike I loved dearly, but did not work for me. The Nomad is also a lovely bike, and works like a champ in the same conditions with the same loads. Similar geometry overall, but heavier tubing or perhaps the greater top tube slope/longer top tube/shorter seat tube/trussed and longer fork may have changed the resonance with my body/position/whatever. Though very similar in many ways, the bikes are also very different in some key ways that might matter. Or not. I think someday, real-time finite-element analysis may give us the definitive answers we seek when approaching the question of shimmy and its causes/cures.
Ah, this is a mystery that is just going to stay a mystery, I fear!
I think you're right, Jim.
All the best,
Dan.
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We were all expecting a fault with the bike/racks but maybe you have special powers that make bikes shimmy as a side effect ;D
But it just gets to show Thorn quality control is spot on, and so is the warranty :)
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It was the ultra high frequency cerebral wave oscillations that did it ;D
Ian
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Similar geometry overall, but heavier tubing or perhaps the greater top tube slope/longer top tube/shorter seat tube/trussed and longer fork may have changed the resonance with my body/position/whatever.
Then do you still need the seat tube with the extra setback? Did Andy test with that? Such a mystery!
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do you still need the seat tube with the extra setback? Did Andy test with that?
Hi Holly!
<nods> Yes, I still need the long-layback seatpost to get the proper position in relation to the bottom bracket (the seat tube angles on the Sherpa and Nomad are similar).
Such a mystery!
It has me baffled!
Best,
Dan.
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Photos, reports, etc of the new Nomad ??
[edit] Ah, just found your thread in the Member's Gallery that I have missed while out in the wilds of the Red Centre. Cool bike set-up.
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out in the wilds of the Red Centre.
Welcome back! Would love any reports, photos, etc.!
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That's on the 'to do' list. I will get a journal up on CGOAB, but at the moment (along with getting back to work) there are the 700+ photos to sort and edit. I also do have some video from the Go Pro Hero 2, but it tends to lack impact in the generally flat lands with the fish-eye lens.
At the moment there are some photos up here on Facebook (https://www.facebook.com/peter.signorini).