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I have been getting some speed wobbles lately. It has to be under certain conditions like a head/cross wind while descending down a long and fairly steep straight road. I am usually in the drops and if I hit the brakes to shed speed, my bike starts to wobble. It can be scary. I have a 2005 Specialized S-works bike and all the parts are in great shape. My hubs and headset have no play in them. Got any suggestions? I have changed wheelsets to try and fix this problem, but its still there.
 

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tofurkey hunting
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i'm no expert, but typically....relax. bikes are incredibly stable. you will find many debates about high speed wobble if you search these forums. but mostly, tense hands/arms/rider can help allow this. also, try placing a thigh on the top tube. i even like to "pinch" it with both my thighs/knees.
 

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Discussion Starter · #3 ·
Speed wobbles

When the speed wobble happens and I try to pinch the top tube with my knees it makes the wobble worse. The only way that I can get the wobble to go away is to let off the brakes and stand up and back off the seat? I am usually very relaxed while descending and very confident.
 

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a pitted headset is a common cause.

to calm the wobbles, weight the pedals, push down, this lowers the center of gravity.
anytime we tense up the tendency is to pull up from the pedals, puttin more weight on the saddle, raising the center of gravity.


Ordinarybikes said:
I have been getting some speed wobbles lately. It has to be under certain conditions like a head/cross wind while descending down a long and fairly steep straight road. I am usually in the drops and if I hit the brakes to shed speed, my bike starts to wobble. It can be scary. I have a 2005 Specialized S-works bike and all the parts are in great shape. My hubs and headset have no play in them. Got any suggestions? I have changed wheelsets to try and fix this problem, but its still there.
 

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As noted by others, grabbing the top tube with the knees / thighs BEFORE a wobble often keeps it from happening. This also allows you to be lighter with your weight on the bars and seems to help keep it from occuring.
 

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jaded bitter joy crusher
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Zinn wrote last week in VeloNews (http://www.velonews.com/tech/report/articles/9786.0.html) that Craig Calfee reported that wobble is sometimes caused by the fork dropouts not being parallel.
Calfee Design has identified a cause of speed wobble (a.k.a. shimmy) and instability that can be prevented. Speed wobble is a dangerous condition that can cause the rider to lose control of the bicycle and crash. While loose headsets and out of true wheels and frames can contribute to speed wobble, we have found that fork asymmetry can also cause speed wobble.​
 

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Ow, ow, ow!

odeum said:
a pitted headset is a common cause.

to calm the wobbles, weight the pedals, push down, this lowers the center of gravity.
anytime we tense up the tendency is to pull up from the pedals, puttin more weight on the saddle, raising the center of gravity.
Wow, this is so wrong, my head hurts!

A pitted headset causing a shimmy (resonance) is often repeated, but it is a myth. There is no cause and affect between them. Plenty of bikes have pitted headsets and don't shimmy. Plenty of bikes shimmy with perfect headsets. If a bike with a pitted headset shimmies, it just a coincidence, nothing more.

Standing on the pedals does not lower the center of gravity. Center of gravity is at the center of mass, so unless you lower the mass (i.e lower the rider), the mass is just as high as before. However, unweighting the saddle can stop a shimmy, but for a completely different reason. A shimmy is caused by a resonant vibration of the front of the bike. The rider's mass on the saddle is typically the "anchor point" for the flex and vibration of the front of the bike. Getting off the saddle eliminates this "anchor point", instantly changing the resonant frequency, and squeelching the vibration.
 

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Grain of salt

Fredke said:
Zinn wrote last week in VeloNews (http://www.velonews.com/tech/report/articles/9786.0.html) that Craig Calfee reported that wobble is sometimes caused by the fork dropouts not being parallel.
Calfee Design has identified a cause of speed wobble (a.k.a. shimmy) and instability that can be prevented. Speed wobble is a dangerous condition that can cause the rider to lose control of the bicycle and crash. While loose headsets and out of true wheels and frames can contribute to speed wobble, we have found that fork asymmetry can also cause speed wobble.​
I would take Craig Calfee's White Paper with a grain of salt. Firstly, even he admits that the results were unrepeatable, so the contribution of fork assymetry is at best a guess. In addition, he seems to believe that loose headsets and out of true wheels also can cause shimmy, which are also dubious claims.

Shimmy is caused by a lateral/torsional resonance of the front of the bike - that includes the wheel, the fork, the steerer, and the front triangle. A misaligned fork will tend to bias the steering to one side, which would tend to disturb the resonance, and prevent it from building up, rather than cause it. Additionally, a loose headset tends to de-linearize the coupling between frame and fork, also also tend not to tranfer the resonance.
 

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Lighter grip...

Sounds like you are wobbling in the kinds of conditions that would make me want to white-knuckle the bars... which causes my bike to wobble, too. Which is some scary stuff.

For me, I found the following things helped... sort of in order of significance

1) Much lighter grip
2) braking a lot less, or smoother, or by sitting up...
...
3) getting my hands to the tops, elbows in and way down, chest down parallel to the top tube, eyes WIDE OPEN, looking for any hint of danger ahead... I don't know if this helps the wobbles by lowering center of gravity- but I'm descending much faster (2-3 mph) and it's smooth as glass now. That's also accounting for almost a year getting used to the new bike.

well, as a counter to 3) I'd like to add that in nasty cross-winds my buddy with deeper V rims than me blows around a lot more, and as I go faster UP the hills, the less I'm willing to even consider getting blown in to the gravel at high speed by some insane gust in a feeble attempt of immitating the great bike handlers (or insane youth) around my area.

Play safe

'Meat
 

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jaded bitter joy crusher
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Mark McM said:
I would take Craig Calfee's White Paper with a grain of salt. Firstly, even he admits that the results were unrepeatable, so the contribution of fork assymetry is at best a guess. In addition, he seems to believe that loose headsets and out of true wheels also can cause shimmy, which are also dubious claims.
Your comments are thoughtful and perceptive. Thanks.
 

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Question... If your brakes are off center so that one pad touches the rim before the other, maybe leading to more resistance on that side of the rim as the rider applies increasing pressure... could that lead to some sort of change in the front end dynamics that would lead to shimmy or wobble... just wondering if any of you engineering types have any insight here since it is difficult to get both sides perfectly matched.
 

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Won't cause a problem

bc165 said:
Question... If your brakes are off center so that one pad touches the rim before the other, maybe leading to more resistance on that side of the rim as the rider applies increasing pressure... could that lead to some sort of change in the front end dynamics that would lead to shimmy or wobble... just wondering if any of you engineering types have any insight here since it is difficult to get both sides perfectly matched.
The affect you are talking about won't cause a wobble. A wobble is a lateral/torsional resonance, and there is nothing about braking more on one side of the rim than then other which will cause the lateral/torsional oscillation required. Beside, rims are flexible enough that they easily bend sideways a few millimeters, and there isn't as much imbalance between one side of the rim and the other as you might expect.

irregularities in rim sidewalls won't cause speed wobble either. Enough people have had pulsing brakes without wobble to show that.
 

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Clearly high-speed wobble is a complex subject. There are many factors involved. Some tend to discount just how much the rider influences it. Many bikes are ridden that had a speed wobble with one person, yet never with a different person. Like any complex problem, no one thing can be pointed to as the cause, or even the dominant factor.
 

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at what speeds does a speed wobble start to occur? just wondering as i dont think ive ever had one (knock on wood) and ive hit some pretty high speeds on descents (47-53mph). i always tuck one of my thighs onto the tob tube at the start of a descent, never really thought about it.
 

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CC09 said:
at what speeds does a speed wobble start to occur? just wondering as i dont think ive ever had one (knock on wood) and ive hit some pretty high speeds on descents (47-53mph). i always tuck one of my thighs onto the tob tube at the start of a descent, never really thought about it.
I've only had this happen to me twice. Both times were around 45-48 mph (looking at my computer's speed record after the fact). Many other times I've descended that fast or even a good deal faster without wobble, so it's not just the speed.

One time when I got the wobbles it was on very rough pavement and the other time there was a gusting crosswind. In both cases, I was desending in a moderate tuck (but nothing extreme) with my cranks parallel to the ground, hands on the drops, and not braking. In both cases, gently braking to reduce my speed to about 40 stopped the wobble. In neither case was I gripping the bars with white knuckles. One time I was a bit nervous because I was in heavy traffic, but the other time I was alone on the road, descending a hill in a straight line and was as relaxed as could be.
 
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