High speed wobblying

Glenn Spray said:

Hello all,

Don't laugh at this one,butiwas wondering if anyone had any ideaswith regard
to a problem I am having .

After many years awayfrom road racing (20) I got my trusty road bike out and
refurbed it and started training again .

The problm is when I hit top speed The front of the bike starts to wobble /
vibrate violently from left to right which as you can imagine is a little
bit annoying /as well as terrifying .

What does anyone think it could be : os a; the wheel bearings ? or the fork
ball bearing races

The problem also is aggravated when going downhill at pace .

thanks for any help

It's called "shimmy".

Read the thoughts of Jobst Brandt, the arch-curmudgeon of rbt, on the
causes of shimmy:

http://www.sheldonbrown.com/brandt/shimmy.html

Glenn Spray said:

Hello all,

Don't laugh at this one,butiwas wondering if anyone had any ideaswith regard
to a problem I am having .

After many years awayfrom road racing (20) I got my trusty road bike out and
refurbed it and started training again .

The problm is when I hit top speed The front of the bike starts to wobble /
vibrate violently from left to right which as you can imagine is a little
bit annoying /as well as terrifying .

What does anyone think it could be : os a; the wheel bearings ? or the fork
ball bearing races

The problem also is aggravated when going downhill at pace .

thanks for any help

Glenn

http://www.sheldonbrown.com/brandt/shimmy.html

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

Tony Raven said:

Glenn Spray wrote:

Quoted message said:

Quoted message said:

The problm is when I hit top speed The front of the bike starts to
wobble / vibrate violently from left to right which as you can imagine
is a little bit annoying /as well as terrifying .

Quoted message said:

http://www.sheldonbrown.com/brandt/shimmy.html

I suspect that if you speed up a bit, it will go away.

Al C-F said:

Tony Raven said:

Glenn Spray wrote:

Quoted message said:

Quoted message said:

The problm is when I hit top speed The front of the bike starts to
wobble / vibrate violently from left to right which as you can
imagine is a little bit annoying /as well as terrifying .

Quoted message said:

http://www.sheldonbrown.com/brandt/shimmy.html

I suspect that if you speed up a bit, it will go away.

The Chuck Yaeger approach!

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

Glenn Spray said:

Hello all,

Don't laugh at this one,butiwas wondering if anyone had any ideaswith regard
to a problem I am having .

After many years awayfrom road racing (20) I got my trusty road bike out and
refurbed it and started training again .

The problm is when I hit top speed The front of the bike starts to wobble /
vibrate violently from left to right which as you can imagine is a little
bit annoying /as well as terrifying .

What does anyone think it could be : os a; the wheel bearings ? or the fork
ball bearing races

The problem also is aggravated when going downhill at pace .

thanks for any help

Glenn

Mine was went away whilst holding the handlebars when I had the frame
re-tracked. Then went away for no handed riding when I replaced the bent
handlebars.

Tony Raven said:

Al C-F said:

Tony Raven said:

Glenn Spray wrote:

> The problm is when I hit top speed The front of the bike starts to
> wobble / vibrate violently from left to right which as you can imagine
> is a little bit annoying /as well as terrifying .

Quoted message said:

http://www.sheldonbrown.com/brandt/shimmy.html

I suspect that if you speed up a bit, it will go away.

The Chuck Yaeger approach!

The Alan Holmes approach!

"Tim Binns" <[email hidden]> wrote

[snip]

Quoted message said:

It's called "shimmy".

Read the thoughts of Jobst Brandt, the arch-curmudgeon of rbt, on

the

Quoted message said:

causes of shimmy:

http://www.sheldonbrown.com/brandt/shimmy.html

I had it once. I attributed it to a "brinelled " headset, i.e. a
headset with dents in the race, owing to the ball bearings having
been hammered into the race, thanks, I think, to the poor state of
the roads in Washington DC.

Anyway, after a new headset, the problem didn't come back

Jeremy Parker

in message <[email hidden]>, Glenn Spray

(') said:

Hello all,

Don't laugh at this one,butiwas wondering if anyone had any ideaswith
regard to a problem I am having .

After many years awayfrom road racing (20) I got my trusty road bike
out and refurbed it and started training again .

The problm is when I hit top speed The front of the bike starts to
wobble / vibrate violently from left to right which as you can imagine
is a little bit annoying /as well as terrifying .

What does anyone think it could be : os a; the wheel bearings ? or the
fork ball bearing races

It's a dynamic speed wobble. They aren't unknown; most of us have
probably had one at one time or another. Any structure has a harmonic
frequency. You can't prevent your bike having a harmonic frequency, but
you can change the one it has. One solution is to change the weight of
the steering bit - the front wheel, stem and handlebars. If you've got a
bar bag, take it off. If you haven't got one, get one and put it on -
and put some weight (e.g. your water bottles) in it.

This won't stop the wobble, but it will change the speed at which it
happens, hopefully to one you never ride at.

If you're thinking of another bike, stiffer frames are on the whole less
susceptible; but /every/ bike has a harmonic frequency.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; This email may contain confidential or otherwise privileged
;; information, though, quite frankly, if you're not the intended
;; recipient and you've got nothing better to do than read other
;; folks' emails then I'm glad to have brightened up your sad little
;; life a tiny bit.

Glenn Spray said:

Hello all,

Don't laugh at this one,butiwas wondering if anyone had any ideaswith regard
to a problem I am having .

After many years awayfrom road racing (20) I got my trusty road bike out and
refurbed it and started training again .

The problm is when I hit top speed The front of the bike starts to wobble /
vibrate violently from left to right which as you can imagine is a little
bit annoying /as well as terrifying .

What does anyone think it could be : os a; the wheel bearings ? or the fork
ball bearing races

The problem also is aggravated when going downhill at pace .

It's a holistic behaviour of the bike + rider combination and not easy
to track down. It is not caused by a loose headset, but it can be
caused by poor steering geometry, odd weight distribution (do you sit
really far back or really far forward?) bent frame/forks or something to
do with resonant frequencies in the road surface and the bike.

The way to stop it when it happens is to lay one thigh on the top tube
to damp the vibrations, and relax your grip on the bars. Curing it
permanently is difficult and there is no logical place to start swapping
components.

Glenn Spray said:

What does anyone think it could be : os a; the wheel bearings ? or the fork
ball bearing races

I had a particularly bad episode when descending Garrowby Hill in the
Yorkshire Wolds a few years ago; in my case it was caused by incorrect
dishing of the rear wheel, so maybe this needs checking, i.e. do front
& rear wheels follow essentially the same line when the bike is going
dead straight ahead? If not, this *could* be a cause of your troubles.
As it happens, I'm currently off my bike for a few weeks after another
unfortunate descending episode on Ilkley Moor last Friday evening (out
of which the bike emerged almost unscathed, unlike me). Nothing to do
with speed wobble this time, though, just a combination of taking a
curve too quickly and on the wrong line in the vicinity of a 6ft stone
wall, and maybe tyres not being as grippy as they should be. I was on
the training bike, and its handling through corners isn't up to the
standard of the race bike, which I found out to my cost. Looking
forward to being back on the road, though....eventually :-(

David Belcher

MSeries said:

Glenn Spray said:

Hello all,

Don't laugh at this one,butiwas wondering if anyone had any ideaswith regard
to a problem I am having .

After many years awayfrom road racing (20) I got my trusty road bike out and
refurbed it and started training again .

The problm is when I hit top speed The front of the bike starts to wobble /
vibrate violently from left to right which as you can imagine is a little
bit annoying /as well as terrifying .

What does anyone think it could be : os a; the wheel bearings ? or the fork
ball bearing races

The problem also is aggravated when going downhill at pace .

thanks for any help

Glenn

Mine was went away whilst holding the handlebars when I had the frame
re-tracked. Then went away for no handed riding when I replaced the bent
handlebars.

I had a really bad case of this when on my way back from shopping. I
had a weedy rack, heavily overloaded. Tap the rear of the bike and you
could see the oscillations.

Having this find it's natural frequency was interesting as it was a)
low and b) at a not very high speed.

...d