What to do about speed wobble?

"Chris Walters" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Only just recovered enough from the fright to ask a question following
yesterday's ride.

I was dropping down the hill from Baydon into Lambourn, nice smooth road
~1 in 15-20, 60 km/h, when the whole bike began to wobble violently.

Seemed to start at the back (wind coming from rear at 45 degrees) and then
carry on until it got to the front. I used the rear brake to slow me down
and it didn't really finish until I'd stopped. Started again, and it came
back, slower speed this time. I almost felt as if a tyre had left the rim.
Fine after that, but didn't do any speeds appraoching 60 again (run out of
hills, run out of bottle!)

So the questions:
1) What causes it?
2) What's the best avoidance strategy?
3) What's the best recovery strategy?

It's called 'speed shimmy', and what causes it is explained in some detail
here, amoung other places:
<url: http://www.yarchive.net/bike/shimmy.html>

Rich

In message <[email hidden]>, Richard Goodman
<[email hidden]> writes

Quoted message said:

"Chris Walters" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Only just recovered enough from the fright to ask a question following
yesterday's ride.

I was dropping down the hill from Baydon into Lambourn, nice smooth road
~1 in 15-20, 60 km/h, when the whole bike began to wobble violently.

Seemed to start at the back (wind coming from rear at 45 degrees) and then
carry on until it got to the front. I used the rear brake to slow me down
and it didn't really finish until I'd stopped. Started again, and it came
back, slower speed this time. I almost felt as if a tyre had left the rim.
Fine after that, but didn't do any speeds appraoching 60 again (run out of
hills, run out of bottle!)

So the questions:
1) What causes it?
2) What's the best avoidance strategy?
3) What's the best recovery strategy?

It's called 'speed shimmy', and what causes it is explained in some detail
here, amoung other places:
<url: http://www.yarchive.net/bike/shimmy.html>

Suggestion in the CTc rag a few issues ago to stop it was to rest your
leg against the top tube, this helps damp out the shimmy.

changing the bike setup can help, such as stem length, tyres weight
distribution
--
Chris French, Leeds

chris French said:

In message <[email hidden]>, Richard
Goodman <[email hidden]> writes

Quoted message said:

Quoted message said:

It's called 'speed shimmy', and what causes it is explained in some
detail here, amoung other places:
<url: http://www.yarchive.net/bike/shimmy.html>

Suggestion in the CTc rag a few issues ago to stop it was to rest your
leg against the top tube, this helps damp out the shimmy.

changing the bike setup can help, such as stem length, tyres weight
distribution

Thanks both, now I know the common term, google has opened up a whole
resource for me to scare myself on :-)

Cheers,
Chris

--
_____________________________________________________

Chris Walters
Hungerford, UK
_____________________________________________________

Richard Goodman [email hidden] opined the following...

Quoted message said:

It's called 'speed shimmy', and what causes it is explained in some detail
here, amoung other places:
<url: http://www.yarchive.net/bike/shimmy.html>

Interesting reading. My habit of gripping the top tube with my legs when
coasting downhills may have a beneficial effect above and beyond a vague
feeling of aerodynamics.

Jon

chris French said:

Quoted message said:

"Chris Walters" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Quoted message said:

Quoted message said:

1) What causes it?
2) What's the best avoidance strategy?

Other than always cycling very slowly, I don't think you can avoid it if
your bike is prone to it without changing components and/or riding
position.

Quoted message said:

Quoted message said:

Quoted message said:

3) What's the best recovery strategy?

Gently swerving from side to side worked for me--difficult but is possible
while the bike is having hysterics.

Quoted message said:

Quoted message said:

It's called 'speed shimmy', and what causes it is explained in some
detail here, amoung other places:
<url: http://www.yarchive.net/bike/shimmy.html>

Suggestion in the CTc rag a few issues ago to stop it was to rest your
leg against the top tube, this helps damp out the shimmy.

changing the bike setup can help, such as stem length, tyres weight
distribution

That did the trick for me. Well, I don't know what precisely did it for
me because a lot of thing were changed, like everything! Raleigh Royal:
used to shimmy badly, often; now never does at all. So one thing I can be
sure of is that it's not /purely/ down to frame & forks..... Hold on, I
did change something about the frame: spread stays from 125 to
133mm--probably not relevant though. In fact just putting the stem down
and altering the saddle helped a bit before the major upgrade job.

~PB

On Tue, 28 Sep 2004 00:20:18 +0100, Jon Senior

jon_AT_restlesslemon_DOTco_DOT_uk said:

Richard Goodman [email hidden] opined the following...

Quoted message said:

It's called 'speed shimmy', and what causes it is explained in some detail
here, amoung other places:
<url: http://www.yarchive.net/bike/shimmy.html>

Interesting reading. My habit of gripping the top tube with my legs when
coasting downhills may have a beneficial effect above and beyond a vague
feeling of aerodynamics.

It definitely can help stop the shimmy. One of my bikes will very
often shimmy when I reach a certain speed, clamping top tube between
my thighs controls the wobble immediately.
--

"Bob"

'The people have spoken, the [censored]'

Email address is spam trapped.
To reply directly remove the beverage.

Pete Biggs said:

That did the trick for me. Well, I don't know what precisely did it

for

Quoted message said:

me because a lot of thing were changed, like everything! Raleigh

Royal:

Quoted message said:

used to shimmy badly, often; now never does at all. So one thing I

can be

Quoted message said:

sure of is that it's not /purely/ down to frame & forks..... Hold

on, I

Quoted message said:

did change something about the frame: spread stays from 125 to
133mm--probably not relevant though. In fact just putting the stem

down

Quoted message said:

and altering the saddle helped a bit before the major upgrade job.

~PB

My Royal used to suffer speed wobble when loaded at speeds above 15mph.
Once I got home from my World Tour I got the frame realigned at Jack
Taylors and it has been much much, very nearly perfect since. I put the
problem down to mu cak handed method of spreading the stays and it
being crashed and thrown around at airports. Good old steel can easily
be bent back into shape. On my recent Sottish Tour I had more weight up
front than I used to have and the bike was very stable at speed. NB
None of my ligthweight racing machines have ever suffered such
problems.

"Chris Walters" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Thanks both, now I know the common term, google has opened up a whole
resource for me to scare myself on :-)

Hence the term "scares resource".

--
Dave...

"Call me Bob" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

...clamping top tube between
my thighs controls the wobble immediately.

OooErr Missus!! Fnaar! Fnaar! :-)

--
MatSav

Chris Walters said:

Only just recovered enough from the fright to ask a question following
yesterday's ride.

I was dropping down the hill from Baydon into Lambourn, nice smooth road ~1
in 15-20, 60 km/h, when the whole bike began to wobble violently.

Seemed to start at the back (wind coming from rear at 45 degrees) and then
carry on until it got to the front. I used the rear brake to slow me down
and it didn't really finish until I'd stopped. Started again, and it came
back, slower speed this time. I almost felt as if a tyre had left the rim.
Fine after that, but didn't do any speeds appraoching 60 again (run out of
hills, run out of bottle!)

It's a harmonic vibration of the whole bike. Individual components are
probably not to blame. Basically you have to change things (like tyres
and forks) until it happens to go away, or just sell the bike and buy
something different. Oddly, if you jump off when it's shimmying the
bike will instantly return to normal and ride itself, so the rider
weight and position obviously affect it. Yes, I did do this once,
before anyone asks...

Whatever you do, don't grip the handlebars tighter but do grip the top
tube between your legs (more difficult on a compact frame). This can
damp the vibrations, which motorcyclists call a "tank-slapper".

Dave Kahn said:

"Chris Walters" <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Thanks both, now I know the common term, google has opened up a whole
resource for me to scare myself on :-)

Hence the term "scares resource".

Don't give up the day job :-)

--
_____________________________________________________

Chris Walters
Hungerford, UK
_____________________________________________________

On Tue, 28 Sep 2004 13:03:12 +0100, "MatSav"

matt.savage@No_Spam_Please_I_am_British.dti.npl.co.uk said:

"Call me Bob" <[email hidden]> wrote in message

Quoted message said:

...clamping top tube between
my thighs controls the wobble immediately.

OooErr Missus!! Fnaar! Fnaar! :-)

Hehe, you know, I though *exactly* the same thing when I wrote that.

I used to own a Finbar Saunders t-shirt, I wonder where that went....
--

"Bob"

'The people have spoken, the [censored]'

Email address is spam trapped.
To reply directly remove the beverage.

One potential cause is having the headset just a smidgen too loose.
I had a mild wobble coming down my local 40mph hill, which was at least
mildly alarming. I rechecked the headset and found it had a touch of play
which was just enough to cause a problem; the bike being very stable
normally.

Don't go mad and torque it down tight as that will ruin it - it needs to be
just right.

This isn't necessarily the cause - since all sorts of other things e.g
geometry, too much luggage, etc could all be a factor, but the headset is
easy to fix. I guess wheel wobble - either being out of shape, or loose hubs
could also cause a problem, and be an easy fix too.

As a general rule with fixing things, it usually pays to get everything
correct as it should be before modifying things to make them better if that
makes sense.

Hywel

Hywel Davies said:

One potential cause is having the headset just a smidgen too loose.

I don't believe that is a cause. How can it be?

~PB

Pete Biggs said:

Hywel Davies said:

One potential cause is having the headset just a smidgen too loose.

I don't believe that is a cause. How can it be?

If you are trying to feather the front brake it gets interesting.. been
there.

My headset on the road bike had cracked on the fork crown race. I could
never get it appropriately tight. Bike would still do 45+ without a problem
of wobble.

...d

"David Martin" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Pete Biggs said:

Hywel Davies said:

One potential cause is having the headset just a smidgen too loose.

I don't believe that is a cause. How can it be?

If you are trying to feather the front brake it gets interesting.. been
there.

My headset on the road bike had cracked on the fork crown race. I could
never get it appropriately tight. Bike would still do 45+ without a

problem

Quoted message said:

of wobble.

Based on (a single) experience, so won't satisfy the h**t statisticians
(only joking )

Normally come down my local steep hill flat out at 40mph - no wobble, all
lovely, just normal bounciness over the bumps.
One day got a mildly scary wobble. Checked headset - slightly loose - duly
rectified.
Next, and subsequent times, no wobble, no worries.

It could have been unrelated, but there you go.

Or another way of looking at it, if the headset is correctly set, then it
can't be that then can it ?

Hywel