Wheel wobble

dag_on_a_bike

Not sure where to post this, so here goes.

Bit of an 'off' today, resulting in broken bike and fractured clavicle (hence one handed on the keyboard - apologies for any typos).

Going down hill, straight line descent, at about 30mph. Front wheel starts an uncontrollable wobble, eventually dumping me on the road/verge.

So I can try and avoid an action reply, what is likely to cause this? What do I do to control/stop it if it happens again?

Recently had a week in S. France/Pyrennees yet never experienced it once, despite much longer and faster descents.

All help appreciated, as at 52 I really don't want a repeat. It HURTS!

Monty Dog

Search for speed shimmy or speed wobble - you're not the first to experience the phenomena and won't be the last.

downfader

Crikey, sorry to hear of your accident. Get well soon! No idea as to what caused it though...

nicklouse

http://www.bikeradar.com/forum/viewtopi ... highlight=

same here.

Ivor Sorarse

How bizarre. Have just made my first post on here about the same phenomenon and a search on Google brought me to your post! Sorry to hear of your accident. Hope you make a speedy recovery. Fortunately I managed not to come off but not before sweaty palms and brown trousers!

Sorarse

mercsport

Sorry to hear of your 'off' , and injuries resulting . Yes , the older we get , the more it seems to hurt .

I rode a classic geometry , aerospace bonded , Dural Vitus for years ( like the ones Sean Kelly - and others - rode early in his career ). It managed to near petrify the life out of me on countless occasions ( I don't know about these 'brown trouser moments ' which are always quoted , it's my heart that seems to swell to uncontainable volume when 'certain doom ' threatens ! ) . It was always a lottery on a fast downhill whether a tank-slapper - to borrow a term from motorcycling - happened or not . I seem to remember moments when my top tube appeared , as if viewed with a stroboscope , to oscillate a high frequency , sinuous , 'S' shape . And , I'd suppose the rest of the frame was similarly flexing wildly .
Somehow , I don't know why , it never dumped me . I did develop a kind of relaxed attitude to it when it started up a wobble . It helped . That is , when you automatically tense up and want to grip the bars for dear life - don't . A looser , relaxed ( resigned to your - fate ? ) grip is probably the way to go . If you can keep your wits collected and also bring your knees together to clamp the top tube that may help too .
The link to Sheldon Brown's page on shimmy is a decent summation . There are too many variables to pin it down to one cause .
My personal theory , or , rather , the one that seems to have worked for me , is to get a smaller frame ( in my case , very much smaller ), and , like the racers of today , employ more seat stick-up , longer stem and so on . This will bring you back to where you were comfortable before . Frame material and design is bound to have a bearing on this too ( I'm a convert to titanium ) . There are a few hills around where I live where I can , often enough , bring up 50mph+ on the computer ( it's the one compensation for being heavy and fat ) - the joy ! - only nowadays I do it without the near morbid dread of the 'wobble' happening .

dodgy

Some say that clamping your knees against the top tube during a speed wobble can help.

boybiker

It seems to be very dependant on your bike geometry and your weight, I have been over 45 on my bestest road bike and never had a hint of wobbly wheels.

dag_on_a_bike

Thanks for the feedback everyone.

Strangest thing is I've ridden the same stretch of road previously and perhaps a little quicker.I don't recall any wobble before.

Oh well, it seems to 'just happen'. No doubt I will be petrified for my first few rides when back on the bike.

DavidBelcher

I've had speed wobble some years back; turned out to be due to the wheels not being properly dished, so that they sat a little off-centre in the frame. Might be worth popping your wheels along to the LBS for a quick check-over.

David