High speed wobble question

[Stéphane Tran]

On our ride today through the Highlands I was descending at 55 km/h+ and my front end started a sort of high frequency side-to-side wobble, which was kind of scary at that speed. I was able to slow down to 30 km/h or so and the wobbling stopped. I have experienced this before on my other bike too, usually on high-speed descents but also a couple of times at low speed when I had both hands off the handlebar. Can anybody enlighten me as to a cause and solution?

[leftcoaster]

I've had it happen a couple of times on high speed descents.

What happens is that your front wheel may hit a small stone or something to cause it to wobble slightly in one direction. Your body/hand strength (over)corrects and then has to over-correct back. It's kind of like a pendulum and the only way to stop it is to slow down. It's weird and both times I checked the bike over from top to bottom and found nothing. Don't panic, just slow down and it will go away.

[luke.koolman]

I had the same thing on my old bike. If you can't brake because the wobble becomes to much try squeezing your knees against the top tube, this will help to tighten up your position and reduce the wobble to a manageable amount.

[JohnT]

I had that at even higher speed coming down Mt. Washington. Increasing the pressure on the back brake and reducing it up front helped. Adjusting the headset to ensure it's as tight as possible without grinding bearing might help (but I am sure you've checked that).

JT

[Jimmy]

I'm guessing you put yourself in an aggressive aero position and perhaps had your weight to far forward loading up your front wheel. Keeping an even weight balance by keeping your hips back should correct. Can't see wheel flex or mechanical looseness (beyond the obvious) being your issue.

[Stéphane Tran]

Thanks for the input guys. I don't think it is a mechanical problem with the bike but rather a positioning and weight distribution issue.

[Lister Farrar]

Sounds like it can be frame and wheel design and weight distribution. None of these articles is definitive though. One even says holding on too tight makes it worse! ('when you're scared out of your wits, loosen your grip.' Sure.)

http://www.sheldonbrown.com/brandt/shimmy.html
http://en.wikipedia.org/wiki/Speed_wobble
http://davesbikeblog.blogspot.ca/2005/1 ... himmy.html

[JohnT]

I had a quick look at those articles Lister - Never occurred to me that the oscillations might match human shivering - I was really cold by the time I hit the bottom of Mt. Washington.

JT