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While I know that this issue has been discussed before, I need some help. This past weekend I rode the IMUSA bike course on Saturday as a training ride. Anyone familar with the ride knows the long downhill into Keene. As I got my road bike (not tri bike) up to speed 42 mph and still accelerating I began to have the wobbles!! I was able to control the bike, even though I was sure that I was going to crash. I basically gave my wife (who was riding behind me) a heart attack.
I have had this road for around 2.5 years and I have had the shimmys since getting the bike. However it almost always occurs on a decent and usually shows up at the worse time (ie over 40 mph). While all will tell me to check the headset etc. everything is mechanically fine with the bike. I was wondering if there is anything I could do to stop this from happening. For example, would adding a fork with more rake help? Do I need a new bike? I am no longer comftorble riding the bike the way it is, eventually she will throw me and I am not looking forward to meeting the pavement.
Also for reference, I have been a triathlete for over 8 years, completed two IMs one of them sub-11, so I spend a lot of time on my bikes and I consider my self a good rider. For comparison when I decend in my Cyfac tri bike, I have no problems, in or out of the aerobars at speeds over 50 mph.
Any help would be much appreciated.
Thanks,
Neal Dunn
what wheels?
what tires?
what fork?
Is it the OEM fork?
Does it do it with any wheel set on the bike?
Does it go away if you shift your weight?
Did you have (can you) have your fork tips aligned? (yes that is important but for some reason most people never have it done).
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What if the Hokey Pokey is what it is all about?
It is a custom Columbus Foco bike. WIth an easton Ec70 fork. Mavic Kysirum wheels. Vrendestein (sp?) tires. I have not tried other wheels, however so many people ride with Kysirums I can't believe that is the problem, however the wide spokes may create a problem.
I have never had the fork aligned but I have also never been in a crash so I am not sure why this would be a problem. No brakes rubbing, or anyother mechanical issues I can think of.
I do not know if it goes away if I shift my weight because at that point I am just trying to get the bike under control.
Neal
I would check the direction first...
did you make sure it was tight enough?
Check the rec.bicycles FAQ:
[url "http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html"]http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html[/url]
Shimmy is not related to frame alignment (although an aligned frame is *more* likely to have a high-speed shimmy!).
Ken Lehner
Might not be the wheels, however - it could be a wheel - fork combo.
I would suggest that you install a high quality tube (latex?) and not put anything on the valve stem (meaning nuts or caps). I would also change out your tire. You need to take the wheels off of your wifes bike next time and try it with her hoops. That will at least indicate that is infact your problem.
Any decent shop should be able to check that for for you - free. I have seen brand new forks that were off by 5-8mm at the center point with the Park FFG-1 in the fork.
What I think that some people may take for granted on a bike, is that all car tires are balanced. If your car tire is out of balance by as much as 1/4oz you will feel it driving at 40-50mph. I am certain that I have felt my valve stem causing a bounce in my wheels in fast decents in the past (including the Keene hill at 60+ mph). I actually put stickers on my wheels opposite the valve stem and try to even the weight of my wheels. On my Zipp 909 disk it was kinda handy that there is a giant Zipp sticker on the wheel that with out a tire will always rest down (heavy) and with a tire mounted the wheel is balanced about even.
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What if the Hokey Pokey is what it is all about?
I've seen Leonard Zinn mention many times that larger size frames produce a lot more shimmy than smaller frames. He's had several articles on shimmy in his Q & A on VeloNews/InsideTri. I go poking around there for more ideas.
as for myself, getting an actual mechanic (instead of the high school kids at the LBS) to check it over removed 90% of the shimmy on my 58cm cannondale. he checked the frame alignment, which was fine, adjusted the headset which seemed fine to him, trued the wheels which were not too bad, and dished both the front and rear wheels. the wheels were unadjusted from the factory, but he said they both were significantly out of dish, which would likely cause some wobble.
all things have resonance, and the wobble is just the manifestation of your bikes natural frequency, if you're tall, you probably need to just get used to a certain amount. if you're feeling ballsy, you could just speed up. the harmonics should go away at a different (higher) speed. :)