Speed Wobble! Advice needed.

Mark73

Hi,

I suppose I should kick off by saying that I know this is a fairly well documented problem. But I have never experienced it before, until yesterday evening that is on 35-40MPH descent! on the second ride out on my new Carbon steed (A Cinelli Man Machine,)

Luckily I managed to keep it under control, but the front wheel was all over the place. I thought I was a goner for a few seconds. Very, very scary!

I did a lot of research on it when I got home, and discovered there are quite a few causes and quite a few suggestions to help stop it or prevent it: Knees on top tube, lift off saddle, legs at 3 and 9 etc, lighter grip on bars, move computer magnet etc

My problem/question is. Do I have to resign myself to the fact that this is something that will always happen with my bike or can a few adjustments fix it for good? I have just shelled out the best part of £1500 on this bike (and I absolutely love it) so I would hate to think that this will be something I have to put up with every time I hit 30-40MPH.

I am hoping some of you good folk will have an answer to my dilemma. has anyone overcome the problem with adjustments or does it ultimately mean you have to think about getting another bike?

Thanks

Mark

(Just for the record I am a bit of a lean bloke weighing only 11.5 stone and I am 6 foot. My bike has the standard Cinelli set up that came with the bike including the Cinelli Crabon forks, but I upgraded to Mavic Ksyrium Elites, to which I had just fitted a set of GP4000 700/23 tyres. dont know if that helps, but I thought it must be useful additional info)

IShaggy

My first thoughts would be to check the headset to see if there is any play. If there is then that's the cause. Beyond that then I suspect it's just a matter of relaxing - which is easier said than done after a scare. And knee against the top-tube is how I correct the problem if it occurs - as it's all about resonance apparently, so knee against the top-tube changes the frequency of the frame, and hence kills the resonance.

CiB

Is everything in balance and secure? Tyres up to recommended pressures, neatly and evenly seated on the rims, no play in the hubs, QR properly done up? As above, is the headset correctly adjusted? Wobbles can arise when some minor problem is amplified by the speed, so worth checking that everything is as it should be.

The glib answer to a speed wobble is to ride through it by going faster. Some cars in the 70s had the same problems - ok up to about 45, dire at around 55mph and ok beyond that.

Smokin Joe

It has nothing to do with the headset, hubs or anything else on the bike. Adjustments to these will have no effect.

It is something that can happen on a lightweight bike with a steep steering geometry, in the motorcycle world it is a well known problem on sharp handling sports bikes but never happens on long legged cruisers.

Yours might just have been a one off caused by a sudden gust of crosswind or a particular ripple in the road surface. If it happens again just press your knees against the top tube and that stops it.

Flambes

I've stopped getting severe wheel wobble by shifting my weight right back over the rear wheel on descents, like going down a steep slope on a mountain bike.
Got it a bit the other day when I went over a cattle grid at 40+ mph, but just relaxed and it cancelled out. I've always had speed wobble on lightweight bikes (starting with my Vitus 979), but I now put that down to trying to descend like Sean Yates with my nose well over the stem.

sneakerfreaker

Smokin Joe wrote:

It has nothing to do with the headset, hubs or anything else on the bike. Adjustments to these will have no effect.

I have found 'wobbling' when tyre pressures are low, worth checking..

huuregeil

In answer to your questions - yes, for a given bike, you're always going to suffer it, pretty much, because it's a fundamental issue with a lack of stiffness in the forward triangle. However, this doesn't mean you can't ameliorate things and live quite happily with a bike that suffers from some speed wobble.

I've had a couple of bikes that suffer from this. The main reason is that I'm tall and my centre of gravity is quite high off the ground, plus my bike frames tend to be on the large side, so naturally suffer from a lack of stiffness (think mass on a bendy stick!). One bike i had to sell, it was really flexy and wobbled *real* bad! My current bike is bearable, but does suffer a bit. However, I'm reasonably comfortable with it and riding it down hills is simply a case of adopting a few techniques, which make sense even if your bike doesn't speed wobble. These are:

- Moving weight backwards
- Losening grip on the handlebars
- Unweighting the saddle slightly
- Pedals at 3 and 9 o-clock, thus making your legs work like shock absorbers
- Resting one knee on the top-tube at all times. I also find this makes cornering much more solid feeling.

Do all of these, then you should have no problem. If you still do, or don't feel comfortable, then new frame it is I think. Sitffer forks might help also, but I'm not sure about this.

I'm going to really hunt down stiffness on my next bike to see if I can't eliminate this for good!

PS I'm 6'2" and 12 stone.

Mark73

Thanks so much for all your advice. Its really appreciated. This is such a great forum and the lack of ego's makes it really welcoming.

I have been over my bike with a fine tooth comb, can't find any cracks in the frame, looseness or play in either the wheels or headset. I am going to employ a few of these suggestions/ tips / techniques on my next jaunt downhill and see what happens.

IncidentallyI had my tyres pumped right up to 120PSI I have read in quite a few places that its a good idea to let pressure out and not increase it. don't know if anyone has experience to the contrary but it would be good to know.

Thanks again and keep the suggestions and thoughts coming. Its a horrible experience, so I hope this might also be of benefit to other readers too.

geoff_ss

Smokin Joe wrote:

It has nothing to do with the headset, hubs or anything else on the bike. Adjustments to these will have no effect.

It is something that can happen on a lightweight bike with a steep steering geometry, in the motorcycle world it is a well known problem on sharp handling sports bikes but never happens on long legged cruisers.

Yours might just have been a one off caused by a sudden gust of crosswind or a particular ripple in the road surface. If it happens again just press your knees against the top tube and that stops it.

I'm afraid it does happen on touring motor cycles.

A friend of mine had a Sunbeam S7 (the one with the big fat tyres) which went into a speed wobbles at about 40 mph. The then current theory was that increasing speed helped the bike recover. He was doing almost 60 mph by the time he fell off. Of course that was a long time ago and motor cycles are probably much improved these days and accelerating on a pedal cycle isn't really an option.

The maths concerning the stability of conditionally stable vehicles (like bicycles) is complicated and there are variables that are usually trivial that can come into play after a small disturbance. Getting the rake and trail right by matching forks and head angle is perhaps the most important but other things like weight distribution and the relative stiffness of the components matters too.

We're all doomed

Geoff