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Scared to death on my Dura Ace wheels!(8 posts)

Scared to death on my Dura Ace wheels!IG
Aug 26, 2003 1:52 PM
I need some help:

This morning I was descending a local canyon after an uneventful climb to the top. About halfway down, I was going approximately 30-35 mph when the front end of my bike started oscillating wildly between two corners.

It all happend very quickly and I can't be sure, but it appeared that the front wheel had potato chipped and I was waiting for it to collapse. I thought I was going down, but managed to get the bike slowed down and under control. Post ride there isn't any apparent damage and both wheels are true.

My bike is a Waterford Paramount with a Look HSC3 carbon fork. The wheels are 2002 Dura Ace WH-7700 with less than 500 miles on them.

I recently did a long ride with multiple descents at greater speeds and experienced no such drama. I am more than a little nervous about repeating today's performance and I'm looking for some feedback.

Have you or anyone you know had a similar experience with Dura Ace wheels?

Thanks for reading.

IG
sounds more like the fork nmgtx
Aug 26, 2003 2:46 PM
re: Scared to death on my Dura Ace wheels!Birddog
Aug 26, 2003 3:00 PM
You have a speed shimmy. Try doing it again, and when it starts to shimmy, loosen your grip.Many times shimmy is a product of you and the bike, so loosening "death grip" alleviates it. If that doesn't work, press aginst the top tube with your knees.
Birddog
re: Scared to death on my Dura Ace wheels!Caadrider
Aug 26, 2003 10:46 PM
Look up speed wobble on google, I found an item that solved it for me. Its not the bike but its you. I now stand up when it happens, this stops it. But it takes some guts to do!

Hope you get past it, the wobbles suck!!!!!!
Every Mechanical System has a natural harmonic frequencyKeeponTrekkin
Aug 28, 2003 6:39 AM
... like a guitar string or a car, which has shock absorbers to dampen oscillations. The combination of bike and rider has a natural harmonic frequency too. If it starts and is not dampened, it will get your attention.

All successful strategies for dealing with the problem add dampening like a shock absorber (press your knee against the top tube) or change the natural harmonic frequency (loosen your grip on the handlebars; stand up [so the bike vibrates at a different frequency] or slow down [so the road irregularities which induce and reinforce the vibration come at a different frequency]).

The problem starts when the right circumstances come together, the essential element being that external force which induces and reinforces the vibration which then runs out of control.

It can be hard to reproduce or can happen at the worst time as so many uncontrollable parameters contribute.

These are all good suggestions. It's never happened to me and if it ever does, I hope I can respond with a cool head!

KoT
Every Mechanical System has a natural harmonic frequencyIG
Aug 29, 2003 10:48 AM
Thanks to all who responded.

I agree that I may have had a death-grip on the bars; I was trailing chatty Kathy in a Suburban at the time. Now that I've had time to think about it, I can see where my actions may have contributed to the problem.

And, even though it had never happen before, the variables that lead to the head-shake (motorcycle vernacular) are infinite and may not be duplicated - I'm torn over whether I should even try. Tempting fate and all that.

Thanks again
Each descent will restore some confidence.dzrider
Aug 29, 2003 12:51 PM
After a while you'll be back to normal down hill riding. Some day a few years from now it may happen again. Or, it may not. You can't be sure other than to say you will be scared spitless when it happens.
Every Mechanical System has a natural harmonic frequencyBirddog
Aug 29, 2003 4:48 PM
I recommend that you try to duplicate this with a "death grip". I did, and when I played around a little with it, I found out about how firm a "grip" I should have on the bars. It helped my confidence. The natural tendency is to tighten the grip when the shimmy starts, and doing the opposite takes a little practice and a leap of faith.
Birddog