Speed wobbles

cborrman wrote:
3) are
[quote=cborrman]
3) are obsessed with slicks and weight alone, a bit of tread is a good thing!

:/ tread may be good for off road but with a contact area about the size of a penny (ish) the last thing I would want is bits missing from my road tyre, even in the wet there is enough capillary action from the road surface to remove water – and that’s the only reason tread is needed, moto gp and f1 prove this. perhaps a compound with more grip would be better advice in this situation? imho

Swapping my forks for a
Swapping my forks for a stiffer, heavier, straight-bladed model worked for me. But I was sure there were no defective or misaligned parts, and doing the same may have no effect for you.

The only corrective measure
The only corrective measure when it happens is to grip the top tube with your legs. Helps dampen the oscillations.

I assume you weren’t braking were you? I’ve suffered severe judder when braking at about 30mph. Scares the c–p out of you. The cause was a build up of brake rubber on the rim. Good clean of the rim and blocks – no further problems.

Only time I got a death
Only time I got a death shimmy ( at 75kph ) it turned out later that the bike had a crack around the seat tube/top tube join

I guess this helped it to be less rigid and so more prone to vibration

Having read a couple of the
Having read a couple of the links, getting more weight over the front wheel sounds like a good idea.

as many say above, it should
as many say above, it should not happen at that speed!

My first suspicion is always spoke tension, you would be amazed what a difference it can make. many shops are obsessed with the wheel being perfectly true (which is a huge step above not giving a sh@t if its less than 2mm out!) rather than even tension, fortunately my latest LBS has a physics genius in the workshop and understands that even tension is the key, even if that means the wheel being slightly out, to avoid a myriad of sins, including wobble.

anyway, technical probs aside, which you no doubt have to get a wobble at that speed, to be able to help get yourself out of these and other problems when this happens, in mountainbike world we put a bigger/grippier tyre and/or run less pressure on the front, so the rear should be telling you that you are on the edge before the front does, and is easier to correct a rear slipping than the front. In road world this translates to running 5-10 psi less in the front and or 5/10psi more out back (all other things being equal. ie if you are already running way too little or way too high a pressure in your tyres then 5psi is not going to make a diffierence)

the biggest problem is that in road world a lot of people do the following:

1) run way too much pressure in both tyres: no way out of a wobble: 5/10 psi meams sod all if you are already 20/30psi too high!

2) put a thinner tyre on the front, less grippy tyre at the front, swap a skidded out rear for the front, etc

3) are obsessed with slicks and weight alone, a bit of tread is a good thing!

4) never ride a mountain bike – there is no better way to learn wobble recovery than hacking it on a mountain bike and managing squirm, wobble, traction loss, etc at least once a week/month

sermon over, get your wheels/hubs checked 🙂

dave_atkinson wrote:
If you

dave_atkinson wrote:

If you do have an unbalanced wheel, then you can balance it by weighting it like you would a car wheel. a bit of extra inner tube inside the tyre can be enough to balance things out.

I never thought of using inner tube, i did an “old skool” scalextric trick that used to weight the back of the car down a bit, a lump of blue tack 🙂

I’m familiar with speed
I’m familiar with speed wobbles on 4 wheeled boards – longboards and mountainboards – but on 2 wheels it’s a different phenomenon. It could be, as Dave suggested, a slightly misbalanced wheel, or something in the road surface resonating with some part of the bike geometry (this seems more likely – have you done that descent at that speed before?)