Speed Wobble!

[bikeman66]

Hi all,

This is predominantly a post to try to settle a point of curiosity more than anything else!

Talking to mate the other day, who runs, cycles, does triathlons, ultra marathons etc etc, we got talking about big rides we had done recently when he said about a trip to Norway last summer. He said he had been descending a long hill at speed, when he got what he described as a "serious speed wobble". Apparently, he couldn't do anything to ride it out and ended up having to gingerly slow down and stop. He inspected his bike and there were no mechanical reasons or other issues that might have caused this. He re-mounted and finished his ride.

Talking to another cyclist, he was told that certain aluminium frames can reach a critical frequency of vibration, which can in turn induce a speed wobble. I had never heard of this, and to be honest, find it slightly far-fetched. Any of you guys experienced this yourselves, or perhaps heard of it happening?

 

[Hacienda71]

I have had a speed wobble on an aluminium bike and ridden with someone having a speed wobble on a carbon framed bike. I think frame material is unlikely to make any difference.

 

[oldroadman]

Probably caused by a headset not being properly adjusted, or a wheel alignment (frame?) problem. In any case the way to stop a wobble is simply to clamp the top tube with your knees and put a bit more weight on the bars. Fixed. Slowing down means you go through all the problems at a slower speed.
Never heard of a problem with aluminium frames as described, if there was one the makers would soon find out (from users) and would have to sort it.
Was your mate using tri-bars? This is not a good control position at high speed (80km/hr plus), being a bit stretched can have some odd effects.

 

[Tim Hall]

It's a resonance thing. A combination of tyre size, tyre pressure, frame geometry, frame material, rider weight, rider size, rider position and a few others.

 

[Slioch]

The only speed wobbles I have had were on a fully laden touring bike on a steep, long & fast downhill freewheel. As suggested above, clamping the top tube between the knees brings things back under control again.

 

[kiriyama]

I had one of these once. Wet day, tailwind, 80kph. ... absolutely pood my pants. Just slowed down slowly, the wobble didn't stop till I stopped. Less a vibration, more a sort of slow wavey feeling. Felt a bit like aquaplaning. Bizarre.

 

[Fab Foodie]

It's a resonance thing. A combination of tyre size, tyre pressure, frame geometry, frame material, rider weight, rider size, rider position and a few others.

This ^^^
All you need to know is here: http://www.sheldonbrown.com/brandt/shimmy.html
I go with Jobst.

 

[Broadside]

It is a horrible thing to experience, I have had it on my alu road bike and my carbon one. A mate had it on his carbon road bike, so straight after I took it down the same hill at the same speed and it was fine. It happens when a number of frequencies line up and you get that resonance and then the amplitude picks up. Horrible.

I have put it down to not having enough weight on the bars. You can induce it with lightly loaded bars, but I find it will steady down if you put more weight on them. Trouble is once it starts you tend to lean back away from it, but what you need to do is lean in. Easier said than done when it is happening though!

 

[2IT]

Hi all,

This is predominantly a post to try to settle a point of curiosity more than anything else!

He said he had been descending a long hill at speed, when he got what he described as a "serious speed wobble". Apparently, he couldn't do anything to ride it out and ended up having to gingerly slow down and stop. He inspected his bike and there were no mechanical reasons or other issues that might have caused this. He re-mounted and finished his ride.

Any of you guys experienced this yourselves, or perhaps heard of it happening?

This happened to me on and off and I finally found out what caused the serious wobble on the downhill. I was only tightening the quick lease levers with my fingers, not hand tight.

I take my wheels on and off after every ride to put it in the trunk of the car where it's safe and dry. There were times riding wondering why I was so shaky that day. It didn't happen the same way every ride. Was I losing my nerve on the downhills? Was it the tremors in my left hand? Some days were fine and others were pretty scary.

Then I was on a club ride with a former pro and it happened. It scared the blank out of me because we were hitting the downhills pretty fast. At the stop sign I was shaking. The pro told me my wheels were too loose with "Finger tight is not tight enough". He used the palm of his hand to do both the front and back wheels. The rest of the ride was fine. Using my full hand to tighten the quick release lever has taken care of the problem since.

Good luck.

 

[RedRider]

I have had a speed wobble on an aluminium bike and ridden with someone having a speed wobble on a carbon framed bike. I think frame material is unlikely to make any difference.

I've had it on steel.I was descending behind a mate who didn't see so was a bit confused by my gibbering afterwards.

 

[Levo-Lon]

In my experience they have all been down to the tyres and too much throttle..motorbikes..
Tarmac shimmy and tar ,white lines etc..once it has upset the bikes steering it just gets worse..
grip top tube or tank and gentle deceleration..or wheelie lol..

i had one on a test ride on a new Yamaha exup ..serious tank slapper..the front tyre was too hard..
to this day i dont know how i saved it..

 

[Julia9054]

It is a horrible thing to experience, I have had it on my alu road bike and my carbon one. A mate had it on his carbon road bike, so straight after I took it down the same hill at the same speed and it was fine. It happens when a number of frequencies line up and you get that resonance and then the amplitude picks up. Horrible.

I have put it down to not having enough weight on the bars. You can induce it with lightly loaded bars, but I find it will steady down if you put more weight on them. Trouble is once it starts you tend to lean back away from it, but what you need to do is lean in. Easier said than done when it is happening though!

This.
It has only happened to me once and, funnily enough, I had been reading about it on here the week before so I knew what to do.
I was descending at about 30mph when a mahoosive lorry overtook me. It gave me plenty of space but due to the speed I was going, I felt a bit scared and automatically tensed up and leaned back. Felt like the front wheel was made of cheese! I lifted my weight off the saddle and leaned in and it stopped.

 

[ColinJ]

I witnessed it happen to the same rider twice in the same place, on different bikes, in different weather conditions (LINK)! That makes me think that riding style is a big factor. I was on the same high speed descent just behind him and had no problems.

 

[raleighnut]

I've had it in cold weather, generally when I've not long set off, on a couple of my bikes it can get pretty bad and the stiffer framed ones (531 and 653 steel) are the worst. Set off by shivering I think.


Shimmy that concerns riders the most occurs with hands firmly on the bars and it is rider generated by muscular effect whose natural response is the same as the shimmy frequency, about that of Human shivering. Descending in cold weather can be difficult for this reason. The rider's "death grip" only enhances the incidence of shimmy in this situation. Loosely holding the bars between thumb and forefinger is a way of avoiding shimmy when cold.
(copied from Sheldon)

 

[Broadside]

I witnessed it happen to the same rider twice in the same place, on different bikes, in different weather conditions (LINK)! That makes me think that riding style is a big factor. I was on the same high speed descent just behind him and had no problems.

I agree, it is mostly rider induced IMO.