Thorn Cycles Forum
Technical => Wheels, Tyres and Brakes => Topic started by: bikerwaser on August 16, 2012, 06:38:15 PM
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Hi All
just recently purchased a Thorn Sherpa and it's a great bike but i'm getting fork vibration at low to medium speeds (8 mph to 15 mph).
it's fitted with Rigida Grizzly's and Panracer tourgaurd tyres.
i've tried towing in the pads more and also tried a different make which helped very slightly.
i've read a few posting on other forums about this topic but wondered if anyone here could help.
a posting on here on a similar vein mentioned having different weighted rims.
i was wondering if anyone else is using this rim/tyre combo and getting the same problem?
any input is appreciated.
thanks !
BikerWaser
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can't help sorry my sherpa is solid as a rock.
is your headset adjusted properly check for any movement.
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Hi Warren,
Welcome to the Forum!
I'm so sorry you're having problems with a fork vibration on your new Sherpa.
I urge you to contact Thorn Cycles at the earliest possible opportunity to ask for their help and assistance. I have found them to be very helpful in every way, and they have a vast store of experience on which to draw for problem-solving.
Meantime, can you tell us a bit more about the fork vibration?
Here's some questions that might shed a bit more light on the issue --
= Does it occur all the time, or only during braking? Heavy braking?
= On all road surfaces?
= When loaded, or riding unladen?
= Do you experience vibration in corners or while just riding along?
Some suggestions...
= Have you checked to see if the headset is properly adjusted? No matter how carefully installed, I have seen headsets (particularly the lower cup) settle farther into the head tube with use, causing them to effectively loosen. My guess at this point is the headset adjustment...worth checking first.
= It is possible the centering cone or other interior headset part is inverted from its usual position. If you have the usual FSA Orbit headset, you can check it against the diagram here: http://img87.imageshack.us/img87/5164/fsaorbitxliidiagram.jpg
= Check the quick-release on the front hub to make sure it is tight and the hub/wheel is properly centered in the fork with the hub fully in the dropouts.
= Check to make sure the v-brake bolts are tight in their mounting bosses.
= Try switching to Kool-Stop Salmon-colored brake pads if you have a set available. They do have different friction characteristics than the stock Shimano offerings.
Hoping this helps!
Best,
Dan.
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Hi Dan
thanks for your reply.
i did contact Thorn but they said they haven't ever had any problems. they said that maybe the pads would settle in.
i had an issue with a previous bike. a felt qx80. their was no fork vibration when i bought the bike but the hub had problems so i changed the wheel and got severe fork vibration. i tried everything. the only thing that worked in the end was to use the existing rims that came with the bike . i had to rebuild the wheel myself.
i've heard of the brake pads you mentioned and may give them a go.
i don't think it's any of the other things you mentioned. it has to be some sort of incompatibility between the pads and rims.
i've noticed that mavic do rims that address this issue. i wonder if anyone else has tried them.
thanks again
Bikerwaser
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Hi Bikerwaser
It is still not quite clear to me whether vibrations occur during braking or when you ride along, but if the latter then I had a very similar problem on my Raven, and vibrations occurred (or where most noticeable) at medium speeds. In the end it turned out it was a problem with my front hub (new XT hubs are really rather useless). Servicing the hub and putting in new bearings sorted this out right away.
So maybe try another wheel, if you have a pare set, and see if this makes a difference for starters (if it dues then you know it's not the frame or the headset). If you don't have another 26' wheel, you may try spinning the front wheel to see if there is any friction or noise in the hub. It should be very smooth, slightest friction or noise would suggest it's servicing time (and with my XT hub this was afetr 6 months use and 2,000k so I really wasn't entirely happy with that).
Good luck!
Kuba
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Thanks Kuba
i have the standard Deore hub but will try another wheel.
also... Dan, I forgot to answer the questions you asked me:
it does happen all the time at the speeds mentioned.
it only happens while breaking on all surfaces but when on a track or the like it's less noticable as the vibration is mingled with the bumps in the track.
it also happens on corners.
it happens only at the bottom of the fork which sounds similar to another posting on this forum about a Thorn Raven.
thanks again Dan for your input. i've read quite a few of your posting and their very helpful.
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Mick F had juddering brakes after fitting new rims, once the brake area wore down a bit the problem went.
see: http://forum.ctc.org.uk/viewtopic.php?f=5&t=55031 (http://forum.ctc.org.uk/viewtopic.php?f=5&t=55031)
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I also had "BAD VIBRATION'S" when I was running "Paul's" brakes >:( only fixed by fitting Avid Shorty 6 Cyclocross Brakes in place of the U.S. made "Paul's".
???
Pete...........................
;)
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Are you using CSS rims? I have a similar experience at low speeds when braking hard with CCS rims, especially in wet weather. Typically, for example, when just coming to a stop on a steep incline for a junction.
A friend with a Sherpa had no such issue until she fitted CSS rims after her old rim wore out. the judder then appeared.
I have had the same thing on both a Raven and another frame/forks.
My experience is that it gets better as the rims wear in a bit but doesn't disappear. However, I think I have modified my breaking technique to accommodate the judder as it rarely happens!
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god you lot a very unlucky with your bikes the only problem i have with mine is i can't go fast,other that that perfect ::)
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Oh, my bikes go very very fast ;D
Seriously though, the judder only happens on occasions. When it is very wet and on steep slopes (at least 20% hills) and at low speed.
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thanks everyone for your input. i've just tried a wheel of my mountain bike. with an "Araya TM 820" rim and the vibration wasn't there at all.
it seems the same as when i had problems with my Felt QX80. there was problems with the hub so i just changed the whole wheel. with a different wheel i got fork vibration so i built up a wheel myself using the new hub and the old rim. the vibration was gone again meaning that it's deffinately the rim.
my issue now is what to do about my Rigida Grizzly rim? do i go for a Rigida Andra which is a bit heavier but that would probably have the same rim surface.
one thing i've thought of is trying the Mavic XM 317 which is lighter and has so called "UB control machine sidewalls for efficient braking". i wonder if anyone has these ?
thing is i could try these and they may not work . another posting on this forum about a Thorn Raven was talking about there could be an issue with using a lighter rim with heavier spokes.
if anyone has any more advice it would be appreciated.
thanks
Bikerwaser
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Take heart, Warren; I'm sure we can solve the problem -- or at least identify it -- through collective effort.
Another couple threads you might find helpful if you haven't seen them already are here:
http://www.thorncycles.co.uk/forums/index.php?topic=4025.0
http://www.thorncycles.co.uk/forums/index.php?topic=3563.0
1) First question, so we know for sure what we're dealing with --
*Are your Rigida Grizzly rims CSS or plain?*
From the sound of it, I would guess they have the Carbide SuperSonic sidewall treatment, but we need to know for sure.
2) The Rigida Andra rim has the same substrate (alloy) but is a different extrusion and weighs more because there is more material (it is intended for heavier-duty use). The Andra also uses no rim eyelets -- instead, it has a center-rib as part of the extrusion, and this rib has cupped nipple seats that work with the nipple to provide a ball-and-socket effect so the spokes take a more direct route to the hub. So far as I have seen, the Rigida Andra and Grizzly have the same sidewall surface, depending of course on whether they are plain or CSS-treated.
An illustration of the Andra in cross-section is here:
http://www.jejamescycles.co.uk/product-images-large/rigida-andra-30-mtb-rim-black-51412.jpg
The Grizzly is shown here:
http://www.jejamescycles.co.uk/product-images-large/rigida-grizzly-700c-se-road-rim-black-51469.jpg
3) Rigida (the company) has been through a number of changes recently, and they aren't done yet. Please see a thread I contributed to here: http://www.thorncycles.co.uk/forums/index.php?topic=3571.0 The upshot of it is, some people have noticed variations in their rims depending on where and when they were made. This is referenced nicely in the CTC link Erudin provided earlier, here: http://www.thorncycles.co.uk/forums/index.php?topic=3571.0
4) Mavic's "UB Control machine sidewalls" is their term meaning the rim sidewalls have been lathe-turned to provide a consistently level surface and parallel sidewalls (or, as they put it, "Usiné Brut Control. The braking surfaces are milled to improve braking friction and eliminate shuddering". "Usiné Brut" is French for "Gross machined"). The process is not unique to Mavic, and the two sets of Rigida Andras currently in my possession all have similarly machined sidewalls. Same with a pair of Alex Adventurers in 700C size (and those are very poor stoppers; go figure). Grant Petersen of Rivendell has written about machined versus plain rim sidewalls here: http://www.rivbike.com/kb_results.asp?ID=52
The topic is discussed further here:
http://www.thechainlink.org/forum/topics/machined-vs-nonmachined?commentId=2211490%3AComment%3A164858
http://bostonfixed.us/forum/comments.php?DiscussionID=1961
http://www.bikeforums.net/showthread.php/346535-Brakes-w-Non-machined-Rims
Mavic's ceramic-coated offerings (as distinct from Rigida's Carbide coatings) tend to fare less well than Rigida's CSS in the wet, and there have been reports on other forums of very poor wet-weather braking and the occasional cracking aroound the spoke nipples or of cracks through the ceramic on Mavic sidewalls.
5) The issue with building light rims with heavy spokes relates to distortion around the spoke holes. Light rims built with heavy spokes show evidence of this with continued braking -- those wheels develop a dot-and-dash pattern on the sidewalls below each spoke hole where the extrusion has bulged from the greater localized tension. This eventually wears even, but can be an issue at first, especially when braking in the wet. Generally -- unless there is some special need -- I prefer to match the spoke gauge to the rim to prevent such problems. So do most wheelbuilders.
I so hope something in this post will help. It is a frustrating problem that interferes with the pleasure of riding and yes, it does appear to be the rim that is contributing directly.
Best,
Dan.
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Mick F had juddering brakes after fitting new rims, once the brake area wore down a bit the problem went.
see: http://forum.ctc.org.uk/viewtopic.php?f=5&t=55031 (http://forum.ctc.org.uk/viewtopic.php?f=5&t=55031)
+1 to Erudin's advice ... Bikerwaser, your problem sounds very much like brake judder to me.
Don't go changing rims or anything drastic until you've given the Brake blocks a chance to wear in.
As in Hamish and Dan's posts above it would be useful to know if you have CSS rims, and I would add it would be useful to know which brake blocks you used to begin with and which ones you changed to.
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Hi Dan and Relayer
thanks for your replys.
i'm not using the CSS rims, just the normal ones.
the pads i started out with were shimano pads that are fitted as standard on the Sherpa.
i changed to a cheap set bought from Asda ( i know that probably sounds like sacrilege on such a wonderful bike but i've found them to work really well. they definitely make the fork vibration a little better).
as you say Relayer , i won't go changing (reminds me of a Barry White song) for the moment. will give the pads a while longer to bed in or in actual fact it's more the rims which should smooth down presenting me with my own "UB control" rims.
Dan .... can i ask you , as you seem extremely knowledgeable , with regard to the lighter Mavic rim , which is about 100grams lighter than the Rigida Grizzly's , would that make a difference in this case ? in other words, would they be too light a rim for the spokes that came as standard with the bike ?
thanks again for all your input.
Bikerwaser
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i'm not using the CSS rims, just the normal ones.
Okay! That helps a lot; thanks.
the pads i started out with were shimano pads that are fitted as standard on the Sherpa. i changed to a cheap set bought from Asda
I would definitely suggest a change to Kool-Stop Salmon pads as the next step to try. If you're using (or still have) the Shimano pad holders, Kool-Stop make a Salmon cartridge pad insert that slips right into the same holder, replacing the original Shimano pad. Much nicer to carry only the cartridge inserts on-tour, as they require less space in your kit. Given their low rate of wear and how "kind" they are to rims, they will last you a long time, so are a good value for the money.
with regard to the lighter Mavic rim , which is about 100grams lighter than the Rigida Grizzly's , would that make a difference in this case ? in other words, would they be too light a rim for the spokes that came as standard with the bike ?
Yes, I would probably go to a 15ga (1.8mm) spoke with the Mavic instead of the 14ga (2.0mm) spokes used on the Grizzly.
But first, I would have a good talk about your intended use, your own weight, the weight you intend to carry, and the roads you'd be using the bike on. The Mavics would simply build-into a lighter wheel overall, and that is a huge consideration. Those are all things I would want to know before building a set of wheels for someone -- and the same questions I ask myself when building my own.
But wait...there's more!
It doesn't appear possible to do a simple "rim swap", as the ERD (Effective Rim Diameter) of the two rims differs. ERD is "...the rim diameter measured at the nipple seats in the spoke holes, plus the thickness of the two nipple heads. The E.R.D. is needed for calculating the correct spoke length" (ref. Sheldon Brown, http://sheldonbrown.com/gloss_e-f.html ).
According to SJS Cycles ( http://www.sjscycles.co.uk/mavic-xm317-26-%28559%29-mtb-all-mountain-rim-silver-prod10607/ ) the Mavic XM317 has an ERD of 539.5mm (for the rim-brake, non-disc version; SJSC carry only the 32-hole version at present).
SJS Cycles say the Rigida Grizzly has an ERD of 534mm ( http://www.sjscycles.co.uk/rigida-grizzly-26-%28559%29-mtb-rim-black-36-hole-prod18844/ ).
[Please note: The ERDs listed for these two rims vary widely depending on vendor and spoke-calculator listings; be sure to check the ERDs are all for rim-brake versions.]
According to SJSC's listings, the spokes used to build the Rigida wheel would be too short for re-use in the Mavic. The thought of a direct rim-swap may not have crossed your mind, but I thought I'd mention it, since you had rebuilt the Felt wheels reusing the same rims.
Best,
Dan.
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A possible ready solution to your problem might be here:
http://www.thorncycles.co.uk/forums/index.php?topic=4509.msg21890;boardseen#new
...a 26'' Rigida Grizzly MTB front wheel for sale by a new member in our Forum's Bike Bits/Accessories For Sale board. Handbuilt by Thorn for a Sherpa, minimal mileage, same kind of wheel, but evidently working well for the seller (Disclaimer: I have no interest in the sale).
Best,
Dan.
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wow !
thanks for the info Dan.
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fork vibration gone now after 2000 miles. it would seem that my initial thought was right about the rims being the issue. after they get ground down the surface becomes smoother. only thing is it was a bit frustrating having to wait 2000 miles until i got rid of it. my only thought now is when i want to replace my front Rigida Grizzly do i go for another one ( because i like the wheel ) and put up with another 2000 miles of "bedding in" or try a different wheel with machined rims?
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Wonderful news, Warren, glad the vibration is gone! Followups like this are really helpful to others with similar problems; thanks!
As for what next...that's a tough question. I have sometimes seen individual differences between rims when building. You might not have the same extended break-in period the next time around. The Grizzly is a popular rim, and the vibration problem is not widely reported, so you might have gotten a bad example.
It would be interesting to see if swapping brake pads now made a difference. I doubt it would, or would be worth the effort, but it would tell you for sure if the problem was the rim or the pads.
Me? I'd leave it alone now it is working fine! :D
Best,
Dan.
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HI Dan
changed the pads recently and still no vibration. so it all points to the "bedding in" of the rims.
Bikerwaser
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changed the pads recently and still no vibration. so it all points to the "bedding in" of the rims.
Oh, this is grand news; wonderful!
I've flagged this topic for future reference in the event others report similar problems. It is a matter that arises from time to time on other bike-related Fora but seldom is there any sort of long-term followup, so it is hard to pinpoint a definitive causality.
In this case <nods> yep! Sure does seem to be a case of the rim bedding in; your initial thought was right indeed. If it helps as an additional data point, the non-CSS Rigida Andra rims on my Nomad now have a darker gray "braking track" where the Kool-Stop salmon pads have been in contact, so some sort of deposition/oxidation is occurring. I can't put it down to any significant rim wear, as the machined ribs are still there to catch my fingernail and I really can't measure any loss of aluminum compared to new. Similar effects have occurred with rims on my other bikes, so yes, "bedding in" sounds like a reasonable explanation.
Thanks for the followup; best wishes for many troublefree rides ahead,
Dan.