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Speed wobbles


Audible Anarchy
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Hi All

 

Id like to find out if anyone has experience with speed wobbling road bikes and what solutions fixed the problems.

 

Ive had a new road bike for around 7000kms now and as of today have had 3 x serious wobbles - the latest at around 70km/h. The other times i could stop it by clamping the top tube with my knees and moving the weight a little forward. but this mornings one was no joke.

 

2 of the incidents were going down the dainfern dip and the other was on a relatively flat road at much slower speed around 35km/h

 

I'm now puzzled as to what could be causing it? I've read all the theories about harmonic resonance etc... Bike has been serviced regularly, headset is not loose, wheels are fine etc...

 

the only thing I've changed on the original bike was put on a shorter stem when i did the initial setup, could this be the problem? whats confusing the most is that it doesn't happen all the time - e.g. i hit over 90km/h defending boulders during jock without any issues.

 

Pls if anyone could help offer some advice? its seriously messing with my head and confidence.

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The only time I ever feel a wobble like that is when I have one hand on the bars. Then the one arm is working overtime to steer and keep balance and it wobbles a bit but this is only when picking up a lot of speed down a mountain. Flat road its more stable.

 

Since you are only getting it now after 7000km, from the sound of it sound like something is wearing out. How was your tyre pressure as well? I think if its too hard then it could do that as well.

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first time was about 2000kms in. 2nd at approx 6000kms (the slower one) and the other today.... all with hands on the bars.

 

bike was serviced about 2 weeks ago. i can't see anything mechanically wrong? maybe is should try a longer stem .. its an XL frame with a 80mm stem - I'm gonna put the orig 100mm on again and see...

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On my MTB I had an issue where one of my brake pads were slightly rubbing on my rotor. Big downhill, touch my front brake and the bike would become uncontrollable from wobbling. SERIOUSLY scary. It messes with your head big time.

 

Can't help with your issues, but I know how you feel. Perhaps take it to your LBS and ask them?

 

Good luck dude.

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Yeah the 100mm stem should be better to level out the reach. Maybe there is a bit too much weight on the front with the shorter stem or the geometry is not what the designers designed the bike for. Perhaps keeping the bike as close to stock in terms of geometry will help stabilize it.

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The more nervous you get, the tighter you grip, the worse the wobble becomes - at least, that's my experience. I think Traaidmark also has a point. How does your bike feel on a flat road if you take your hands off the bars? Should give an indication if she's too twitchy - my headset was a fraction loose and she behaved like a baitch with PMS.

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The more nervous you get, the tighter you grip, the worse the wobble becomes - at least, that's my experience. I think Traaidmark also has a point. How does your bike feel on a flat road if you take your hands off the bars? Should give an indication if she's too twitchy - my headset was a fraction loose and she behaved like a baitch with PMS.

 

i generally only take my hands off the bars when I'm going say under 30km/h and it feels fine - i have to plant my weight a little more forward than with previous bikes I've had, but it feels solid?

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A mate of mine had the same problem last year. I have been riding bikes for a loooong time, so as good engineers do, we applied some good problemsolving techniques, but I could not solve the issue. Then he mentioned that he pumped his tyres to between 10 and 11 Bar!!!!!!

 

WOW

 

Dropped the pressure to something more reasonable, and problem fixed!! Seems that this might not be your issue?

 

Also check if your headset is pitted?

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This topic has been commented on here on the hub - I think under "shimmy" or "high speed shimmy". It is caused buy a wave like resonance developing in the bike similar to a wheel wobble in a car with an unbalanced wheel. Can have a host of causes - from rider tension to wheels to fork alignment and everything in between. Once you have eliminated any obvious damage as a cause you are reduced to resting a leg on the top tube or gripping the tube with your knees. My solution was to change my frame. I could control my bike but could not get up the confidence to really let loose on the descents. I suspect that my build (long legs, short trunk) was not compatible with the very compact frame I had. The distance from BB to top tube was short relative to the top tube to saddle measurement. My new frame is less compact and I have had no hassles.

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A mate of mine had the same problem last year. I have been riding bikes for a loooong time, so as good engineers do, we applied some good problemsolving techniques, but I could not solve the issue. Then he mentioned that he pumped his tyres to between 10 and 11 Bar!!!!!!

 

WOW

 

Dropped the pressure to something more reasonable, and problem fixed!! Seems that this might not be your issue?

 

Also check if your headset is pitted?

 

Pitted?

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Pitted?

 

Lift up the front of the bike and turn the steering from side to side. Does it have a notch in the straight ahead position or can you feel many notches from side to side?

 

Does the wheel "fall" left and right under its own weight?

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Lift up the front of the bike and turn the steering from side to side. Does it have a notch in the straight ahead position or can you feel many notches from side to side?

 

Does the wheel "fall" left and right under its own weight?

 

aaah, like when you ride on rollers too much - i had that happen to an old bike i had? no i reckon this headset is fine? all very confusing indeed....

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Pitted?

 

Yep, haven't open up a headset in a while, but the essence is that if a headset was slightly loose, the bearings us to hit smallist indents on the surface its runs on - "pitting" the surface, so when the headset is tightened, the bearings naturally tends to try to move towards those indents, with the result that the steering is less than smooth. Again, not sure if that can cause speed wobble, but hey at least you eliminated a possible cause!

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In my experience (I am no expert BTW, so feel free to flame, I can take it ;) )

 

Wobbles can be caused by a few things. I believe 2 of them to be:

 

1. Your headset bearings have a problem.

 

2. You don't have enough weight on the front of the bike, which comes down to the fact that the bike is not set up correctly for your build.

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