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Speed wobble


Shaunpr
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50km may not be super fast but hitting tar at that speed is the problem

Its just strange that getting a speed wobble at that speed, normally on a windy ride get 75km/h and no wobble. What bike is it? How old the tyres? Something not right if wobbling at 50km/h

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I seem to catch a speed wobble around the same area on a pretty fast decent, the bike goes into a serious wobble, the first time I used brakes to slow down but it actually made it worse so now I try peddle through it. What would be the cause of this and what can I do to stop it from happening. The bike is sized right for me so I am puzzled and pretty scared too.

You say you get a wobble with and without braking, but braking makes it worse.

 

Start by standing over your bike (feet on the floor and your bike between your legs - some people I know don’t understand cycling jargon).

Pull the front brake and then try rock the bike forwards and backwards. If you get movement in the fork/steerer, then chances are your headset is (1) worn, or (2) loose. Get it checked out.

 

As for the tips on lowering your centre of gravity... drop your chest as low over the bars as possible, to lower the CoG and to put more weight over the front wheel. Try this at slower speeds and gradually ramp the speed up. You’ll find you’ll be able to take corners at higher speeds too.

 

The tip about leaning on your outside pedal works, but also requires practicing it at slower speeds and building up the speed from there.

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Its just strange that getting a speed wobble at that speed, normally on a windy ride get 75km/h and no wobble. What bike is it? How old the tyres? Something not right if wobbling at 50km/h

Canyon Ultimate SLX, tyres Conti 5000 tubeless 28mm

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You say you get a wobble with and without braking, but braking makes it worse.

 

Start by standing over your bike (feet on the floor and your bike between your legs - some people I know don’t understand cycling jargon).

Pull the front brake and then try rock the bike forwards and backwards. If you get movement in the fork/steerer, then chances are your headset is (1) worn, or (2) loose. Get it checked out.

 

As for the tips on lowering your centre of gravity... drop your chest as low over the bars as possible, to lower the CoG and to put more weight over the front wheel. Try this at slower speeds and gradually ramp the speed up. You’ll find you’ll be able to take corners at higher speeds too.

 

The tip about leaning on your outside pedal works, but also requires practicing it at slower speeds and building up the speed from there.

Thanks will certainly look at the fork/headset.

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Check the tyre for a bulge anywhere on the casing. Often hitting cateyes or shards of glass with a cut through a ply (Conti's are 3 ply like good  toilet paper). If this happens then the plys below can start to slide over each other creating a slight bulge before developing a hop. Spinning the wheel should reveal it quickly enough.

 

Headset should be tensioned correctly.

 

A large tyre imbalance can also cause this. Are you running the tyre  tubeless and is the sealant still liquid? if you have a lot of dried sealant collecting at one point it will be a large  mass causing the imbalance.

Maybe using a longer heavier valve than the wheel was supplied with?

 

Could be the rim has a heavy spot.

 

Are your wheel bearings running with a lot of play in the bearing?

 

Then harmonics is the other issue. Could be a combination of weight speed and imbalance combining so changing the weight or balancing something rotating better than current helps

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Canyon Ultimate SLX, tyres Conti 5000 tubeless 28mm

 

 

I run the identical combination with the DT-swiss PRC 1400 Disk wheels and have (touch wood) not experienced anything like this.

 

D&D above has listed some of the causes for creating the harmonics, check them out.

 

Ultimately, it is a combination of weight, speed, frame, wheels, tyres, road condition, etc and speed that causes it. Change any one of those and the wobble won't occur. 

 

Apparently, you can accelerate the shimmy away, although I don't know anyone brave enough to have done that.... 

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Speed wobble is to cycling what like swing is to cricket, many different theories.

 

Apparently it is not harmonics, it’s a nonlinear bifurcation phenomenon called “Hopf Bifurcation.” Wtf?

 

Lennard Zinn has written extensively about it, you will find a lot on Velonews.

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Speed wobble is to cycling what like swing is to cricket, many different theories.

 

Apparently it is not harmonics, it’s a nonlinear bifurcation phenomenon called “Hopf Bifurcation.” Wtf?

 

Lennard Zinn has written extensively about it, you will find a lot on Velonews.

 

 

a Hopf Bifurcation isn't as severe as mechanical resonance i.e. the structure usually won't shake itself apart. It's a point of rising instability which then abates once you go over it. Sort of like the sound barrier for a layman example.

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Check the tyre for a bulge anywhere on the casing. Often hitting cateyes or shards of glass with a cut through a ply (Conti's are 3 ply like good  toilet paper). If this happens then the plys below can start to slide over each other creating a slight bulge before developing a hop. Spinning the wheel should reveal it quickly enough.

 

Headset should be tensioned correctly.

 

A large tyre imbalance can also cause this. Are you running the tyre  tubeless and is the sealant still liquid? if you have a lot of dried sealant collecting at one point it will be a large  mass causing the imbalance.

Maybe using a longer heavier valve than the wheel was supplied with?

 

Could be the rim has a heavy spot.

 

Are your wheel bearings running with a lot of play in the bearing?

 

Then harmonics is the other issue. Could be a combination of weight speed and imbalance combining so changing the weight or balancing something rotating better than current helps

Agree with Diesel, I would not ride on that part of the road until you have sorted it out.

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50km/h is a bit slow to get a speed wobble. I got one on suikerbossie at 75km/h, there's a section half way down where the wind comes off the left and there's a bit of buffeting which can set it off.

Check both wheels are centered front and rear. Also, I have found that it definitely helps if you keep the pedals turning.

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