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High speed wobble question(10 posts)

High speed wobble questionwolfereeno
Nov 5, 2002 12:21 AM
Woa - I've been getting high speed front wobbles at around 35 mph when I start braking on a slightly rough downhill.
On smoother roads I've been able to go faster than this with no wobbles. I don't know if it's the bike, road, or my nerves. I'm probably a bit white knuckled on the washboard stuff. And to make it scarier, feathering the brakes to slow down slightly suprisingly doesn't really help much.

This happend while going down Bear Mountain in NY the other day. The road's not that great and coupled with the traffic and hikers on the road I was not really at ease.

I'm ridding a new bike- 51" Kestrel 200sci, kestrel fork, and Cosmos. I've read in other msg threads to have the headset tightened and will look into that, but it doesn't seem loose to me. Also other threads have suggested that the frame is flexy but it's a pretty stiff carbon frame.

Is it more mechanical or is it me? Any suggestions or should I just relax, clamp the seat tube with my knees, and pray...

Thx
-Bill
re:I had a bike that did this very unpredictably.dzrider
Nov 5, 2002 7:55 AM
After the first few instances any time I felt the wobble start I'd let go of the bars for a few seconds and the bike would kind of right itself and act normally. Others have suggested knees against the top tube, but since my present bikes don't have the problem I can't comment on that cure.

The problem had nothing to do with the headset and may have had something to do with head winds. I believe, without being able to explain it, the theory about sympathetic vibrations. Holding the brakes made it feel even worse.

If you're talking about the narrow, winding road on the east side of the Bear Mt bridge, I'd figure something out before trying that one again. I found it pretty scary w/o speed wobbles the one time I rode through there.
Not too unusual...some possible causes:retro
Nov 5, 2002 8:33 AM
That comes up here from time to time, and people have suggested some possible fixes. Headset is the main one; also make sure the wheel is true and properly tensioned. Swap tires front to rear to see if that cures it, or borrow a front wheel/tire from a friend and try that.
FWIW, I had a Motobecane years ago that had a bad wobble at about 35, and nothing we tried made any difference. I don't go that fast very often anyway, so I finally just lived with it. Touching the brakes lightly seemed to help.
That road's downright nastyvelocity
Nov 5, 2002 9:15 AM
Definitely confirm that your bike is mechanically sound but, knowing that descent, and since you say the wobble doesn't occur otherwise, I'd guess that the wobble is caused by the downright nasty road surface and your "white-knuckled" braking.
That road's downright nastywolfereeno
Nov 5, 2002 12:40 PM
Thanks all, especially NJ/NY guys.

The other location that I always feel close to being out of control is flying down Sheriff's Hill in Palisades State park. Just a little bit of roughness along with trying to brake starts the wobbles. The roads a little rough but not like potholes or anything.

I guess I'm too used to 2" wide MTB tires - this is my first roadbike.

-Bill
nasty, nasty, nastywolfereeno
Nov 5, 2002 12:57 PM
My best most terrifying downhill ever (I prefer going up hills!) was in the desert in Las Vegas on a rented full suspension mountain bike with sh*tty brakes. The hill was a jeep road at the very end of the ride as we headed back to the van. It wasn't that steep but was about a mile long and totally straight. There were rocks everywhere and gulleys on each side. Since I couldn't get the brakes to slow me down, I just hung on for dear life which was passing before my eyes. That moment of taking my fingers off of the brake levers altogether so I could concentrate on holding onto the bars was pretty intense!

Once I was at the bottom, it actually seemed better that I had let myself roll down the hill and let momentum do its thing. But that's a tough leap of faith. And the thought of crashing on a road versus dirt makes it even scarier.

One of these days maybe I can bomb sherrif's hill without touching the brakes at all. (I'll probably be doing 60 before flying off the cliff.)
re: High speed wobble questionHeron Todd
Nov 5, 2002 2:55 PM
Check the FAQ:

http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html

Todd Kuzma
Heron Bicycles
LaSalle, IL 815-223-1776
http://www.heronbicycles.com
re: High speed wobble questionwolfereeno
Nov 5, 2002 4:20 PM
Thanks! Interesting article.

Makes sense that the bike+rider system is ocsillating at some natural resonant frequency.

Their suggestion is to just get up out of the saddle.

While it makes sense that moving what amounts to the node of the standing wave (the non moving portion of the oscillation - ie: where my ass meets the bike) would change the dynamics of the system, common sense suggests that standing would be even less stable. The natural tendancy is to clamp everything down and hold on tight. But if the theory in that article is true, that would make it even worse.

Very interesting if that's all it takes to stop it. I'll have to give it a try :-)
Rim problem?Kerry
Nov 5, 2002 5:23 PM
If this is only triggered by braking, you might examine the rim braking surface. If there is any uneven surface or surface contamination, then the rim could be grabbing with braking. That might trigger oscillation that would otherwise not occur.
re: High speed wobble questionpcmtngoat
Nov 6, 2002 11:57 AM
I've had frame wobble on two bikes and have searched for the solution. There are a lot of different opinions and as far as I know, no definitive answer. I got an expensive DeRosa Merak in hopes of curing the problem and was dismayed when I got severe wobble at 40+ MPH going down a steep canyon with a head wind. I had the frame checked, got new wheels Ksyriums, etc. and still had the problem. Pinching the top tube helped some but I don't like having to do that or worry about the problem occuring. I finally decided that one last solution could be the forks. Mine were CF 1" Time forks from the first year DeRosa used them. They have since gone to a much beefier fork. I put on Ouzo Pro forks and have not had wobble since! I'm on a much larger frame- 59- and that is supposed to be one of the potential causes. If possible you could try swapping out the fork for a ride and see if that cures it. People who haven't experienced high speed wobble have no idea how bad it can be. Good luck.