"Speed Wobble"

[I.OWN.U]

I always try go balls to the wall be it going up a hill or down it.... Then a couple of weeks ago, coming back from the cradle on on one of the bigger downhills doing about 65km/h my bike started to wobble to the point that I almost lost it, gave the bike a once over on the side of the road and all seemed fine. Got back on and a bit rattled slowly made my way back home.

Mate told me my back wheel was not true and I then thought that might be the "Wobble" problem.

Took the back wheel to lbs to have the hub serviced and wheel trued. Got the wheel back a bit later and went for another ride.... same thing this time starting at 50km/h.

Can anybody please give me some advice or tell me why I would suddenly be getting these "wobbles"

Really breaking my confidence on downhill sections

[seven]

From the net.

 

1. Sometimes speed wobble can result simply because of a poorly manufactured and designed frame. The wheels may be misaligned (front wheel and back wheel aren’t tracking in the same spot) and the bike is fighting itself. There are very few frames this poorly made these days, but you’ll still find them.

 

2 A scenario seen relatively often is that the top tube of the bike is under-built. If you put a lot of weight on the saddle the front end of the bike can pivot around the seat tube and create oscillation. An under-built top tube isn’t stiff enough to stop that from happening. Another thing that can happen is that the trail (the product of head angle and fork rake) of the bike is too large. What happens is that the bike becomes too stable at speed and the large trail over corrects itself and brings the wheel past center, and the wheel moves back and recorrects itself again which is where the wobble comes from. This is relatively common problem that Baum tells me he’s seen in the past.

 

3. Incorrect weight distribution is a very common cause of speed wobble. Quite often, speed wobble has just as much to do with the rider as it does with the bike. If speed wobble starts occurring, many people will intuatively put their weigh towards the back of the bike instead of putting their weight towards the front to actually stop it and dampen it out. The best thing to do to get out of a wobble is to weight one of your legs down at the 6/12 o’clock position, put some weight on the front end by bending your elbows (use soft hands – don’t grip handlebars firmly!), and take some weight off your seat (to take the pivot point away) which puts more weight back on the handlebars, which puts more weight on the front wheel. This will usually bring stability back to the bike and correct the oscillation. The reason it’s suggested that the pedals be in the 6/12 o’clock position (rather than the 3/9 o’clock position) is because this will bring your body weight into a better balanced position which will calm the bike down.

 

Different riders may experience speed wobble on different bikes. A bike can descend like a dream for one rider, while another will get the fright of his life on the very same bike. Things like stem length on a particular geometry and weight distribution of the rider can have a lot to do with it.

Edited January 11, 2014 by seven

[-Az-]

On a motorbike I could help so for now I can only offer this -->http://cyclingtips.com.au/2011/03/speed-wobble-when-the-bike-shakes-its-head/

[David Marshall]

Extensivly covered under "shimmy" or "high speed shimmy" some time ago. Horrible and can have any number of reasons to set it off. In most cases it is niether the bike nor the rider but a combination of both. A frame change sorted mine out.

[I.OWN.U]

Thanks so much SEVEN , -Az- and David Marshal al you comments and links have been very informative reading I now also think its a combination of me and my bike.... will definitely take all this info onto my ride tommorow....

[Cellar]

Have you ridden the same section at the same speed before with no problem?

[I.OWN.U]

Same section same speed and or Faster before..... I have been fiddling with riding position and cleat and seat adjustment.... will reset and see if it still continues

[LeTurbo]

Try this: clamp your top tube between your legs. It seems there's a kind of resonance that sets up through the frame - of course, braking only makes it worse. But gripping the middle seems to deaden the effect.

[Cheese]

Had the same issue for the first time a tear or so ago and then again in the 94.7 last year. reading up a lot and of the things Seven explains the bike design very rarely still a problem unless a different bike. With me same as you once it happened to you, you are now scared of it happening again making you more tense and ensuring it actually happens more.

 

I still need to test a bit more, but what I have found is that you need to pedal, the fact that you are tense make you to stop pedalling as you are afraid to loose control. Get more weight on the front wheel, this I did by adjusting my seat forward.

 

It happened to me in the double century and a team mate fell back speaking to me telling me to pedal, which I did and we went down fast without the wobble occurring again.

 

The wobble occurs at more or less the same frequency as the human shiver, so being do not be tense and grip the bar to hard, get to front of saddle. I will also report back on my next downhill her later this week.

[kosmonooit]

There was a discussion on the phenomenon on Velonews recently

 

Bifurcation and high-speed shimmy

 

 

Follow up here