Sherpa Shimmy resolved with superb warranty response by Thorn Cycles

[Andre Jute]

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

[Danneaux]

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!"  

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.

[philb0412]

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

[Danneaux]

...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!" 

Congratulations

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.

[jags]

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

[triaesthete]

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

[JimK]

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!

[Danneaux]

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.

[Danneaux]

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.

[Andre Jute]

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

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

[Danneaux]

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.

[Relayer]

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.

[mickeg]

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.

[Andre Jute]

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

[Danneaux]

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.