Speed wobbles on a carbon fork?
 

About a year ago I was coasting down a hill (20 mph) without my hands on the bars and my fork started wobbling a disturbing amount, it looked like it was about to snap. I grabbed the bars and started pedaling again, all was fine.

That incident was the only time I have gotten any sort of wobble/play out of the fork until last night. I was on a longer descent, spinning away on a higher gear when my left foot unclipped. At this point I was riding at ~32 or so. The second my foot unclipped my fork started wobbling violently again. My weight was displaced a bit when my foot unclipped, when the fork took its first wobble the whole bike got thrown to the right.

I was able to straighten out, that said, what's going on? I have been over 40 mph on her without any problems. I assumed it was just when I was riding hands free, but, even then it seemed a bit out of the ordinary, no?

That happened to me last year at about 35 mph. Scarred me, turns out I didn't have my stem tightened down far enough on my fork, there was a bit of wobble. I tightened it better and the wobble is gone......

I've heard others here speak of a wobble having something to do with harmonic vibration. One poster awhile back said that he would touch his knee to his frame and the wobble would go away...........

Shoulda used Tegaderm. Now you know.

It is an issue of harmonic vibration. So lots of thing change the equation, including speed, weight distribution etc.

Make sure everything is adjusted correctly. If the wobs happen, press a knee into the TT. Or HTFU and accelerate.

on fast descents i have had this same issue on my caad-9. i have tried the knee theory and it works great and has helped pull me out of the dreaded head shake. just press a knee into your top tube on a descent and not worry anymore.

Thanks guys. Scared the **** out of myself on that descent the other day. I'll check the headset tightness as well—honestly the whole ride is probably due for service.

Danke.

We had a friend break his collarbone this May on a descent down a mountain on the Blue Ridge Parkway. He is a really tall person on a large frame. His bike shook violently and he crashed.

Examination of causes is that it is believed the front wheel was not tightened (clamped/skewered) properly that morning and this was the first downhill of the day. The wheel was mis-aligned.

He exacerbated the problem by unclipping. We had not heard of the "press knee into frame" at that time but I now preach it to fellow riders when we are doing hills and to have them double check their front wheel as well.

Other posters to this problem mention that poor tolerances (out of quality spec.) front forks can cause this problem and this makes sense to me.

Might want to check your front fork. I would advise to get this fixed or disaster could occur in the future. I would not ride this bike on a hill until fixed.
Regards, curtwally

I just about lost it at 46mph on Carson Pass this past weekend due to speed wobble. The bike is fine. Everything is true, tight, and good.

It was an issue of harmonic oscillation. I'm tall, the bike had a long wheelbase, etc. Perfect conditions for it.

I didn't know about the knees on the top tube trick, so I consider myself lucky to have not lost a lot of skin.

Just read up about speed wobble on wikipedia. You can even watch a video of a guy inducing it and correcting it on youtube. It's no longer scary.
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I had a crack in the steerer tube. That crack was hidden by the head tube. I think that's what caused the wobble.

I don't think everything is fine if you get this speed wobble. Something is terribly wrong and needs fixing. Bikes should not be sold that cannot go 50mph down a hill without wobble. What bike/fork is this and frame size?

curtwally