Steering oscillation ... what to do?

[Doug McLaren]

So, I'm riding to work today, on the most scary part of my ride -- 0.6
miles over a bridge on a pretty busy highway with 65 mph traffic. 12"
of unridable curb. (Alas, any other options are miles out of my way.)
It's slightly downhill, so I usually get a pretty good speed going,
perhaps 35 mph if I pedal 25-30 mph if I don't. It's perfectly
straight, and perfectly flat -- no turning, no bumps. It scares me,
but it's usually over in about a minute, so I do it.

Today I'm not pedalling, right in the middle of the lane, and I'm
crouched down on the lower handlebars (no aerobars or anything like
that) and my odometer says my top speed was 28 mph, so that's probably
what my speed was. And then the steering starts oscillating back and
forth, at about 2 Hz. It starts weak, but turns into a pretty strong
oscillation in about two seconds, and I'd say I was a second or two
away from a serious crash. I hit the brakes, and as I slow, the
oscillation goes away.

I stop and walk the bike somewhere safe, and check it out. Wheels are
well secured, steering column is tight, etc. I can't find anything
wrong. I ride it slow at first, no problems, and the later I'm going
down another hill (in a much safer place) and hit 30 mph and no
problems (but so ready to hit those brakes!)

It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
much stock, except that it has 700x28c tires, and a luggage rack. And
interrupter brake handles, but I wasn't on the top part of the bars
this time. (This might be relevant -- I do most of my riding with my
hands on the top part of the bars. I don't race, I just ride for
exercise, fun and to get from point A to B.)

The bike is pretty new to me, but I'm not the first owner. I've
personally only got about 70 miles on it now. No problems like this
before, but this was probably the fastest I'd been on it until today
too.

This part of my ride makes me nervous, and so I might have been
holding on tighter than usual, but I doubt I was actually shaking
(well, I was after ...)

I've found a number of pages that talk about this --

http://www.sheldonbrown.com/brandt/shimmy.html
http://en.wikipedia.org/wiki/Speed_wobble

.... but I don't really know what to do about it. I was pretty close
to losing it, and if I had, it would have been very bad.

One of the articles suggests putting a leg against my top tube, which
I'll try, but is there more that can be done? Something that doesn't
rely on me remembering to ride the right way?

--
Doug McLaren, [email protected]
Marge, this ticket doesn't just give me a seat. It also gives me the
right, no, the duty, to make a complete ass of myself. --Homer Simpson

 

[Tom Kunich]

Congratulations on entering the wobble club. That usually happens with metal
frames and forks when you hit the front wheel EXACTLY right. Above or below
the critical speed you won't get the wobble but once it starts it will often
get progressively worse as you slow up and then at the critical speed it
will simply disappear.

In case it's something else:

1) Hold the front brake on and rock the front end. If it clicks the headset
might be loose or some such. This is an adjustment. This is also somewhat
rare on bikes as new as your Giant.

2) With the front brake on push the front wheel side to side at the forks.
If there's a clicking it can mean that the bearings in the wheel are loose
or bad. This is pretty rare as well.

3) Spin the front wheel and see if you broke a spoke or knocked the front
wheel out of alignment in some manner.


"Doug McLaren" <[email protected]> wrote in message
news:[email protected]...
> So, I'm riding to work today, on the most scary part of my ride -- 0.6
> miles over a bridge on a pretty busy highway with 65 mph traffic. 12"
> of unridable curb. (Alas, any other options are miles out of my way.)
> It's slightly downhill, so I usually get a pretty good speed going,
> perhaps 35 mph if I pedal 25-30 mph if I don't. It's perfectly
> straight, and perfectly flat -- no turning, no bumps. It scares me,
> but it's usually over in about a minute, so I do it.
>
> Today I'm not pedalling, right in the middle of the lane, and I'm
> crouched down on the lower handlebars (no aerobars or anything like
> that) and my odometer says my top speed was 28 mph, so that's probably
> what my speed was. And then the steering starts oscillating back and
> forth, at about 2 Hz. It starts weak, but turns into a pretty strong
> oscillation in about two seconds, and I'd say I was a second or two
> away from a serious crash. I hit the brakes, and as I slow, the
> oscillation goes away.
>
> I stop and walk the bike somewhere safe, and check it out. Wheels are
> well secured, steering column is tight, etc. I can't find anything
> wrong. I ride it slow at first, no problems, and the later I'm going
> down another hill (in a much safer place) and hit 30 mph and no
> problems (but so ready to hit those brakes!)
>
> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
> much stock, except that it has 700x28c tires, and a luggage rack. And
> interrupter brake handles, but I wasn't on the top part of the bars
> this time. (This might be relevant -- I do most of my riding with my
> hands on the top part of the bars. I don't race, I just ride for
> exercise, fun and to get from point A to B.)
>
> The bike is pretty new to me, but I'm not the first owner. I've
> personally only got about 70 miles on it now. No problems like this
> before, but this was probably the fastest I'd been on it until today
> too.
>
> This part of my ride makes me nervous, and so I might have been
> holding on tighter than usual, but I doubt I was actually shaking
> (well, I was after ...)
>
> I've found a number of pages that talk about this --
>
> http://www.sheldonbrown.com/brandt/shimmy.html
> http://en.wikipedia.org/wiki/Speed_wobble
>
> ... but I don't really know what to do about it. I was pretty close
> to losing it, and if I had, it would have been very bad.
>
> One of the articles suggests putting a leg against my top tube, which
> I'll try, but is there more that can be done? Something that doesn't
> rely on me remembering to ride the right way?
>
> --
> Doug McLaren, [email protected]
> Marge, this ticket doesn't just give me a seat. It also gives me the
> right, no, the duty, to make a complete ass of myself. --Homer Simpson

 

[Tim McNamara]

<snip classic description of shimmy>

I find that just slightly standing up on the pedals- just enough to ease
my weight off the saddle, not to actually stand up- stops the shimmy.

 

[[email protected]]

Doug McLaren wrote:

> So, I'm riding to work today, on the most scary part of my ride --
> 0.6 miles over a bridge on a pretty busy highway with 65 mph
> traffic. 12" of unridable curb. (Alas, any other options are miles
> out of my way.) It's slightly downhill, so I usually get a pretty
> good speed going, perhaps 35 mph if I pedal 25-30 mph if I don't.
> It's perfectly straight, and perfectly flat -- no turning, no bumps.
> It scares me, but it's usually over in about a minute, so I do it.

> Today I'm not pedaling, right in the middle of the lane, and I'm
> crouched down on the lower handlebars (no aero bars or anything like
> that) and my odometer says my top speed was 28 mph, so that's
> probably what my speed was. And then the steering starts
> oscillating back and forth, at about 2 Hz. It starts weak, but
> turns into a pretty strong oscillation in about two seconds, and I'd
> say I was a second or two away from a serious crash. I hit the
> brakes, and as I slow, the oscillation goes away.

> I stop and walk the bike somewhere safe, and check it out. Wheels
> are well secured, steering column is tight, etc. I can't find
> anything wrong. I ride it slow at first, no problems, and the later
> I'm going down another hill (in a much safer place) and hit 30 mph
> and no problems (but so ready to hit those brakes!)

> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
> much stock, except that it has 700x28c tires, and a luggage rack.
> And interrupter brake handles, but I wasn't on the top part of the
> bars this time. (This might be relevant -- I do most of my riding
> with my hands on the top part of the bars. I don't race, I just
> ride for exercise, fun and to get from point A to B.)

> The bike is pretty new to me, but I'm not the first owner. I've
> personally only got about 70 miles on it now. No problems like this
> before, but this was probably the fastest I'd been on it until today
> too.

> This part of my ride makes me nervous, and so I might have been
> holding on tighter than usual, but I doubt I was actually shaking
> (well, I was after ...)

You don't need to shake, although that can help initiate shimmy.
Unless you hold onto the bars differently (loose grip) or can calm you
response, you are reinforcing the natural frequency of bicycle shimmy.
Generally the tighter you grip the bars the tenser your arm muscles
are and worry about this occurring, the more certainly it will be
initiated,

> I've found a number of pages that talk about this --

http://www.sheldonbrown.com/brandt/shimmy.html
http://en.wikipedia.org/wiki/Speed_wobble

> ... but I don't really know what to do about it. I was pretty
> close to losing it, and if I had, it would have been very bad.

First you must recognize that your natural response frequency is the
same as the shimmy so even if you are not initiating it, you are
reinforcing it.

> One of the articles suggests putting a leg against my top tube,
> which I'll try, but is there more that can be done? Something that
> doesn't rely on me remembering to ride the right way?

This should become natural to you. I think experimenting would help.
Coast no-hands down a grade where this shimmy speed can be achieved
and see whether it occurs. Then you will know what the natural
critical speed is and know when to be prepared to suppress it.

That it occurs with hands on the bars makes me suspect you are not at
ease at higher speeds. That is another solution.

Jobst Brandt

 

[Tom Kunich]

<[email protected]> wrote in message
news:[email protected]...
>
> You don't need to shake, although that can help initiate shimmy.
> Unless you hold onto the bars differently (loose grip) or can calm you
> response, you are reinforcing the natural frequency of bicycle shimmy.
> Generally the tighter you grip the bars the tenser your arm muscles
> are and worry about this occurring, the more certainly it will be
> initiated,

Hmm I forgot that - most of the shimmy is caused by your fear and the
tightness of your grip on the bars. If you can completely relax that
sometimes stops the shimmy but I was never able to do that. Eventually I
became relaxed enough on the bike that I never gripped the bars tight enough
to support a shimmy.

This is why Jobst is a good addition to this group. He has the ability to
explain all the correct procedures when the rest of us have forgotten it
after learning good practices that prevent such things from happening.

>> I've found a number of pages that talk about this --
>
> http://www.sheldonbrown.com/brandt/shimmy.html
> http://en.wikipedia.org/wiki/Speed_wobble
>
>> ... but I don't really know what to do about it. I was pretty
>> close to losing it, and if I had, it would have been very bad.
>
> First you must recognize that your natural response frequency is the
> same as the shimmy so even if you are not initiating it, you are
> reinforcing it.
>
>> One of the articles suggests putting a leg against my top tube,
>> which I'll try, but is there more that can be done? Something that
>> doesn't rely on me remembering to ride the right way?
>
> This should become natural to you. I think experimenting would help.
> Coast no-hands down a grade where this shimmy speed can be achieved
> and see whether it occurs. Then you will know what the natural
> critical speed is and know when to be prepared to suppress it.
>
> That it occurs with hands on the bars makes me suspect you are not at
> ease at higher speeds. That is another solution.
>
> Jobst Brandt

 

[Mike Jacoubowsky]

> The Brandt article is definitive. Shimmy is a 'phenomenon' not a 'defect'.
> Mike Jacoubowsky reported success with a much heavier weight of grease in
> headset bearings than is normally used. If it's chronic, try that besides
> damping the top tube with your knee
> --
> Andrew Muzi

Wonderful. I don't even remember saying that! OK, I dimly recall it now.
Basically all it did was damp the steering a bit, and the effect would go
away pretty quickly as the grease moves out of place. Maybe I used taffy?

The problem with shimmy is that it's *not* the bicycle, but the combination
of bicycle and rider. A bicycle isn't inherently stable; if it were, you
could give it a push and get it to head down the road a ways. In all cases
(with normal bikes) the bike is dependent upon rider input for stability.
Which is a problem, since a nervous rider does things that reinforce a
tendancy to shimmy. It's all in the FAQ, but I don't think the FAQ hits hard
enough on the fact that a bicycle is inherently unstable until you add a
person to it. That should be enough to get people thinking in the right
direction.

I actually had a scary bit of shimmy last week, for the first time in ages.
I was heading down the fast, pretty straight grade on Highway 1 towards
Tunitas Creek (Northern California) with my camera in one hand, taking
pictures of the coast, while trying to not lose ground to a fast-moving
group that was a bit ahead of me. I think I got a bit nervous about doing
39mph while taking photos (I generally have a rule of putting away the
camera at 35mph+), and that was all it took to set up the shimmy. I didn't
feel comfortable putting the camera away (so I couldn't get two hands on the
bars) and I was having a very difficult time convincing myself that the
right thing to do was to move my left hand from the brake lever towards the
center of the bar. I *did* know that there was no issue with the bike, and I
*did* know the right things to do. That I resisted doing so is evidence that
even somebody who knows all the right stuff can still have problems doing
the right stuff.

In the future, I'm going to stick to my "no photos above 35mph" rule. :>)

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA




"A Muzi" <[email protected]> wrote in message
news:[email protected]...
> Doug McLaren wrote:
>> So, I'm riding to work today, on the most scary part of my ride -- 0.6
>> miles over a bridge on a pretty busy highway with 65 mph traffic. 12"
>> of unridable curb. (Alas, any other options are miles out of my way.)
>> It's slightly downhill, so I usually get a pretty good speed going,
>> perhaps 35 mph if I pedal 25-30 mph if I don't. It's perfectly
>> straight, and perfectly flat -- no turning, no bumps. It scares me,
>> but it's usually over in about a minute, so I do it.
>>
>> Today I'm not pedalling, right in the middle of the lane, and I'm
>> crouched down on the lower handlebars (no aerobars or anything like
>> that) and my odometer says my top speed was 28 mph, so that's probably
>> what my speed was. And then the steering starts oscillating back and
>> forth, at about 2 Hz. It starts weak, but turns into a pretty strong
>> oscillation in about two seconds, and I'd say I was a second or two
>> away from a serious crash. I hit the brakes, and as I slow, the
>> oscillation goes away.
>>
>> I stop and walk the bike somewhere safe, and check it out. Wheels are
>> well secured, steering column is tight, etc. I can't find anything
>> wrong. I ride it slow at first, no problems, and the later I'm going
>> down another hill (in a much safer place) and hit 30 mph and no
>> problems (but so ready to hit those brakes!)
>>
>> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
>> much stock, except that it has 700x28c tires, and a luggage rack. And
>> interrupter brake handles, but I wasn't on the top part of the bars
>> this time. (This might be relevant -- I do most of my riding with my
>> hands on the top part of the bars. I don't race, I just ride for
>> exercise, fun and to get from point A to B.)
>>
>> The bike is pretty new to me, but I'm not the first owner. I've
>> personally only got about 70 miles on it now. No problems like this
>> before, but this was probably the fastest I'd been on it until today
>> too.
>>
>> This part of my ride makes me nervous, and so I might have been
>> holding on tighter than usual, but I doubt I was actually shaking
>> (well, I was after ...)
>>
>> I've found a number of pages that talk about this --
>>
>> http://www.sheldonbrown.com/brandt/shimmy.html
>> http://en.wikipedia.org/wiki/Speed_wobble
>>
>> ... but I don't really know what to do about it. I was pretty close
>> to losing it, and if I had, it would have been very bad.
>>
>> One of the articles suggests putting a leg against my top tube, which
>> I'll try, but is there more that can be done? Something that doesn't
>> rely on me remembering to ride the right way?
>
> The Brandt article is definitive. Shimmy is a 'phenomenon' not a 'defect'.
> Mike Jacoubowsky reported success with a much heavier weight of grease in
> headset bearings than is normally used. If it's chronic, try that besides
> damping the top tube with your knee
> --
> Andrew Muzi
> <www.yellowjersey.org/>
> Open every day since 1 April, 1971
> ** Posted from http://www.teranews.com **

 

[peter]

On Jun 13, 4:28 pm, "Mike Jacoubowsky" <[email protected]>
wrote:
> > The Brandt article is definitive. Shimmy is a 'phenomenon' not a 'defect'.
> > Mike Jacoubowsky reported success with a much heavier weight of grease in
> > headset bearings than is normally used. If it's chronic, try that besides
> > damping the top tube with your knee
> > --
> > Andrew Muzi
>
> Wonderful. I don't even remember saying that! OK, I dimly recall it now.
> Basically all it did was damp the steering a bit, and the effect would go
> away pretty quickly as the grease moves out of place. Maybe I used taffy?
>
> The problem with shimmy is that it's *not* the bicycle, but the combination
> of bicycle and rider. A bicycle isn't inherently stable; if it were, you
> could give it a push and get it to head down the road a ways.

And you can. Sure, it'll eventually fall over when it slows down
enough, but the normal steering geometry does result in pretty good
stability of an unridden bike above 5mph or so (beach cruiser geometry
is better for this than road bike).

Guess you didn't participate in one of my neighborhood's pastimes as a
child. A couple kids would ride their bikes straight toward each
other and then jump off while still a few hundred feet apart. The
idea was to to have the bikes still going fast enough to cause a good
collision (and generate additional revenue for bike shop owners).

I've encountered shimmy a few times and have found the 'knee against
top tube' to work very well at damping the oscillation.

 

[jim beam]

[email protected] wrote:
> Doug McLaren wrote:
>
>> So, I'm riding to work today, on the most scary part of my ride --
>> 0.6 miles over a bridge on a pretty busy highway with 65 mph
>> traffic. 12" of unridable curb. (Alas, any other options are miles
>> out of my way.) It's slightly downhill, so I usually get a pretty
>> good speed going, perhaps 35 mph if I pedal 25-30 mph if I don't.
>> It's perfectly straight, and perfectly flat -- no turning, no bumps.
>> It scares me, but it's usually over in about a minute, so I do it.
>
>> Today I'm not pedaling, right in the middle of the lane, and I'm
>> crouched down on the lower handlebars (no aero bars or anything like
>> that) and my odometer says my top speed was 28 mph, so that's
>> probably what my speed was. And then the steering starts
>> oscillating back and forth, at about 2 Hz. It starts weak, but
>> turns into a pretty strong oscillation in about two seconds, and I'd
>> say I was a second or two away from a serious crash. I hit the
>> brakes, and as I slow, the oscillation goes away.
>
>> I stop and walk the bike somewhere safe, and check it out. Wheels
>> are well secured, steering column is tight, etc. I can't find
>> anything wrong. I ride it slow at first, no problems, and the later
>> I'm going down another hill (in a much safer place) and hit 30 mph
>> and no problems (but so ready to hit those brakes!)
>
>> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
>> much stock, except that it has 700x28c tires, and a luggage rack.
>> And interrupter brake handles, but I wasn't on the top part of the
>> bars this time. (This might be relevant -- I do most of my riding
>> with my hands on the top part of the bars. I don't race, I just
>> ride for exercise, fun and to get from point A to B.)
>
>> The bike is pretty new to me, but I'm not the first owner. I've
>> personally only got about 70 miles on it now. No problems like this
>> before, but this was probably the fastest I'd been on it until today
>> too.
>
>> This part of my ride makes me nervous, and so I might have been
>> holding on tighter than usual, but I doubt I was actually shaking
>> (well, I was after ...)
>
> You don't need to shake, although that can help initiate shimmy.
> Unless you hold onto the bars differently (loose grip) or can calm you
> response, you are reinforcing the natural frequency of bicycle shimmy.
> Generally the tighter you grip the bars the tenser your arm muscles
> are and worry about this occurring, the more certainly it will be
> initiated,
>
>> I've found a number of pages that talk about this --
>
> http://www.sheldonbrown.com/brandt/shimmy.html
> http://en.wikipedia.org/wiki/Speed_wobble
>
>> ... but I don't really know what to do about it. I was pretty
>> close to losing it, and if I had, it would have been very bad.
>
> First you must recognize that your natural response frequency is the
> same as the shimmy so even if you are not initiating it, you are
> reinforcing it.

jobst, he's a piece of floppy harmonic meat. he can't help reinforce it
if his dynamics coincide with that of the bike.



>
>> One of the articles suggests putting a leg against my top tube,
>> which I'll try, but is there more that can be done? Something that
>> doesn't rely on me remembering to ride the right way?
>
> This should become natural to you. I think experimenting would help.
> Coast no-hands down a grade where this shimmy speed can be achieved
> and see whether it occurs. Then you will know what the natural
> critical speed is and know when to be prepared to suppress it.

that is a band-aid and does not fix the problem. worse, it doesn't
prevent it from starting, something a proper cure does.



>
> That it occurs with hands on the bars makes me suspect you are not at
> ease at higher speeds. That is another solution.

typical - blame the rider.

 

[jim beam]

Doug McLaren wrote:
> So, I'm riding to work today, on the most scary part of my ride -- 0.6
> miles over a bridge on a pretty busy highway with 65 mph traffic. 12"
> of unridable curb. (Alas, any other options are miles out of my way.)
> It's slightly downhill, so I usually get a pretty good speed going,
> perhaps 35 mph if I pedal 25-30 mph if I don't. It's perfectly
> straight, and perfectly flat -- no turning, no bumps. It scares me,
> but it's usually over in about a minute, so I do it.
>
> Today I'm not pedalling, right in the middle of the lane, and I'm
> crouched down on the lower handlebars (no aerobars or anything like
> that) and my odometer says my top speed was 28 mph, so that's probably
> what my speed was. And then the steering starts oscillating back and
> forth, at about 2 Hz. It starts weak, but turns into a pretty strong
> oscillation in about two seconds, and I'd say I was a second or two
> away from a serious crash. I hit the brakes, and as I slow, the
> oscillation goes away.
>
> I stop and walk the bike somewhere safe, and check it out. Wheels are
> well secured, steering column is tight, etc. I can't find anything
> wrong. I ride it slow at first, no problems, and the later I'm going
> down another hill (in a much safer place) and hit 30 mph and no
> problems (but so ready to hit those brakes!)
>
> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
> much stock, except that it has 700x28c tires, and a luggage rack.

ok, the luggage rack, if loaded, can easily start an harmonic - [this
has been discussed here before]. were you using it, and what was on it?


> And
> interrupter brake handles, but I wasn't on the top part of the bars
> this time. (This might be relevant -- I do most of my riding with my
> hands on the top part of the bars. I don't race, I just ride for
> exercise, fun and to get from point A to B.)
>
> The bike is pretty new to me, but I'm not the first owner. I've
> personally only got about 70 miles on it now. No problems like this
> before, but this was probably the fastest I'd been on it until today
> too.
>
> This part of my ride makes me nervous, and so I might have been
> holding on tighter than usual, but I doubt I was actually shaking
> (well, I was after ...)
>
> I've found a number of pages that talk about this --
>
> http://www.sheldonbrown.com/brandt/shimmy.html
> http://en.wikipedia.org/wiki/Speed_wobble
>
> ... but I don't really know what to do about it. I was pretty close
> to losing it, and if I had, it would have been very bad.
>
> One of the articles suggests putting a leg against my top tube, which
> I'll try, but is there more that can be done? Something that doesn't
> rely on me remembering to ride the right way?
>

i've experimented with extensively since i had a crash from a
shimmy-prone bike and cracked a hip. pain focuses the mind tremendously.

here's the formula:

shimmy frame + shimmy wheels = disaster.

shimmy frame + stiffer wheels = better, but still not perfect.

stiff non-shimmy frame + stiffer wheels = rock-solid stability.

stiff non-shimmy frame + shimmy wheels = shimmy only if you really try,
and it damps itself quickly.

all this assumes you're not using the rack. if you are and it's loaded,
all the above is academic because racks always have a substantial
lateral flex and therefore harmonic. i suggest back-packing your
luggage as a much safer solution.

 

[jim beam]

A Muzi wrote:
> Doug McLaren wrote:
>> So, I'm riding to work today, on the most scary part of my ride -- 0.6
>> miles over a bridge on a pretty busy highway with 65 mph traffic. 12"
>> of unridable curb. (Alas, any other options are miles out of my way.)
>> It's slightly downhill, so I usually get a pretty good speed going,
>> perhaps 35 mph if I pedal 25-30 mph if I don't. It's perfectly
>> straight, and perfectly flat -- no turning, no bumps. It scares me,
>> but it's usually over in about a minute, so I do it.
>>
>> Today I'm not pedalling, right in the middle of the lane, and I'm
>> crouched down on the lower handlebars (no aerobars or anything like
>> that) and my odometer says my top speed was 28 mph, so that's probably
>> what my speed was. And then the steering starts oscillating back and
>> forth, at about 2 Hz. It starts weak, but turns into a pretty strong
>> oscillation in about two seconds, and I'd say I was a second or two
>> away from a serious crash. I hit the brakes, and as I slow, the
>> oscillation goes away.
>>
>> I stop and walk the bike somewhere safe, and check it out. Wheels are
>> well secured, steering column is tight, etc. I can't find anything
>> wrong. I ride it slow at first, no problems, and the later I'm going
>> down another hill (in a much safer place) and hit 30 mph and no
>> problems (but so ready to hit those brakes!)
>>
>> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
>> much stock, except that it has 700x28c tires, and a luggage rack. And
>> interrupter brake handles, but I wasn't on the top part of the bars
>> this time. (This might be relevant -- I do most of my riding with my
>> hands on the top part of the bars. I don't race, I just ride for
>> exercise, fun and to get from point A to B.)
>>
>> The bike is pretty new to me, but I'm not the first owner. I've
>> personally only got about 70 miles on it now. No problems like this
>> before, but this was probably the fastest I'd been on it until today
>> too.
>>
>> This part of my ride makes me nervous, and so I might have been
>> holding on tighter than usual, but I doubt I was actually shaking
>> (well, I was after ...)
>>
>> I've found a number of pages that talk about this --
>>
>> http://www.sheldonbrown.com/brandt/shimmy.html
>> http://en.wikipedia.org/wiki/Speed_wobble
>>
>> ... but I don't really know what to do about it. I was pretty close
>> to losing it, and if I had, it would have been very bad.
>>
>> One of the articles suggests putting a leg against my top tube, which
>> I'll try, but is there more that can be done? Something that doesn't
>> rely on me remembering to ride the right way?
>
> The Brandt article is definitive.

no it's not! it doesn't properly address frame torsion, lateral wheel
stiffness, or the harmonics between the two.


Shimmy is a 'phenomenon' not a 'defect'.

it's a defect if it's just the frame/normal wheelset. it can and should
be addressed. torsional frame stiffness is the #1 way to cure it. old
frames with narrow tubesets are notorious for this. modern oversize
tubesets are significantly improved. this is not coincidence.


> Mike Jacoubowsky reported success with a much heavier weight of grease
> in headset bearings than is normally used. If it's chronic, try that
> besides damping the top tube with your knee

that's band-aid - doesn't address the cause at all.

 

[[email protected]]

On Jun 13, 5:28 pm, "Mike Jacoubowsky" <[email protected]>
wrote:

[snip]

> A bicycle isn't inherently stable; if it were, you
> could give it a push and get it to head down the road a ways. In all cases
> (with normal bikes) the bike is dependent upon rider input for stability.
> Which is a problem, since a nervous rider does things that reinforce a
> tendancy to shimmy. It's all in the FAQ, but I don't think the FAQ hits hard
> enough on the fact that a bicycle is inherently unstable until you add a
> person to it. That should be enough to get people thinking in the right

[snip]

Dear Mike,

Like you, I thought that a riderless bicycle was inherently unstable
and would topple over shortly after being released.

Several posters enjoyed setting me straight with movies like this:

http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/bicycle_stability.mov

Cheers,

Carl Fogel

 

[[email protected]]

On Jun 13, 6:30 pm, jim beam <[email protected]> wrote:
> [email protected] wrote:
> > Doug McLaren wrote:
>
> >> So, I'm riding to work today, on the most scary part of my ride --
> >> 0.6 miles over a bridge on a pretty busy highway with 65 mph
> >> traffic. 12" of unridable curb. (Alas, any other options are miles
> >> out of my way.) It's slightly downhill, so I usually get a pretty
> >> good speed going, perhaps 35 mph if I pedal 25-30 mph if I don't.
> >> It's perfectly straight, and perfectly flat -- no turning, no bumps.
> >> It scares me, but it's usually over in about a minute, so I do it.
>
> >> Today I'm not pedaling, right in the middle of the lane, and I'm
> >> crouched down on the lower handlebars (no aero bars or anything like
> >> that) and my odometer says my top speed was 28 mph, so that's
> >> probably what my speed was. And then the steering starts
> >> oscillating back and forth, at about 2 Hz. It starts weak, but
> >> turns into a pretty strong oscillation in about two seconds, and I'd
> >> say I was a second or two away from a serious crash. I hit the
> >> brakes, and as I slow, the oscillation goes away.
>
> >> I stop and walk the bike somewhere safe, and check it out. Wheels
> >> are well secured, steering column is tight, etc. I can't find
> >> anything wrong. I ride it slow at first, no problems, and the later
> >> I'm going down another hill (in a much safer place) and hit 30 mph
> >> and no problems (but so ready to hit those brakes!)
>
> >> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
> >> much stock, except that it has 700x28c tires, and a luggage rack.
> >> And interrupter brake handles, but I wasn't on the top part of the
> >> bars this time. (This might be relevant -- I do most of my riding
> >> with my hands on the top part of the bars. I don't race, I just
> >> ride for exercise, fun and to get from point A to B.)
>
> >> The bike is pretty new to me, but I'm not the first owner. I've
> >> personally only got about 70 miles on it now. No problems like this
> >> before, but this was probably the fastest I'd been on it until today
> >> too.
>
> >> This part of my ride makes me nervous, and so I might have been
> >> holding on tighter than usual, but I doubt I was actually shaking
> >> (well, I was after ...)
>
> > You don't need to shake, although that can help initiate shimmy.
> > Unless you hold onto the bars differently (loose grip) or can calm you
> > response, you are reinforcing the natural frequency of bicycle shimmy.
> > Generally the tighter you grip the bars the tenser your arm muscles
> > are and worry about this occurring, the more certainly it will be
> > initiated,
>
> >> I've found a number of pages that talk about this --
>
> > http://www.sheldonbrown.com/brandt/shimmy.html
> > http://en.wikipedia.org/wiki/Speed_wobble
>
> >> ... but I don't really know what to do about it. I was pretty
> >> close to losing it, and if I had, it would have been very bad.
>
> > First you must recognize that your natural response frequency is the
> > same as the shimmy so even if you are not initiating it, you are
> > reinforcing it.
>
> jobst, he's a piece of floppy harmonic meat. he can't help reinforce it
> if his dynamics coincide with that of the bike.
>
>
>
> >> One of the articles suggests putting a leg against my top tube,
> >> which I'll try, but is there more that can be done? Something that
> >> doesn't rely on me remembering to ride the right way?
>
> > This should become natural to you. I think experimenting would help.
> > Coast no-hands down a grade where this shimmy speed can be achieved
> > and see whether it occurs. Then you will know what the natural
> > critical speed is and know when to be prepared to suppress it.
>
> that is a band-aid and does not fix the problem. worse, it doesn't
> prevent it from starting, something a proper cure does.
>
>
>
> > That it occurs with hands on the bars makes me suspect you are not at
> > ease at higher speeds. That is another solution.
>
> typical - blame the rider.

An age ago I was in a group coming down Gates Pass by Tucson, AZ, and
a guy on a tall Colnago Super developed a shimmy. It was crazy; the
rest of us were having a good time and this poor slob was almost
wetting himself, thinking he was going to die. He blamed the bike.
Said the headtube angle was too steep. Of course, this was the early
70s and there was a lot of voodoo in cycling. Now that we have Science
all the voodoo is gone. Right?

tf

 

[jim beam]

[email protected] wrote:
> On Jun 13, 6:30 pm, jim beam <[email protected]> wrote:
>> [email protected] wrote:
>>> Doug McLaren wrote:
>>>> So, I'm riding to work today, on the most scary part of my ride --
>>>> 0.6 miles over a bridge on a pretty busy highway with 65 mph
>>>> traffic. 12" of unridable curb. (Alas, any other options are miles
>>>> out of my way.) It's slightly downhill, so I usually get a pretty
>>>> good speed going, perhaps 35 mph if I pedal 25-30 mph if I don't.
>>>> It's perfectly straight, and perfectly flat -- no turning, no bumps.
>>>> It scares me, but it's usually over in about a minute, so I do it.
>>>> Today I'm not pedaling, right in the middle of the lane, and I'm
>>>> crouched down on the lower handlebars (no aero bars or anything like
>>>> that) and my odometer says my top speed was 28 mph, so that's
>>>> probably what my speed was. And then the steering starts
>>>> oscillating back and forth, at about 2 Hz. It starts weak, but
>>>> turns into a pretty strong oscillation in about two seconds, and I'd
>>>> say I was a second or two away from a serious crash. I hit the
>>>> brakes, and as I slow, the oscillation goes away.
>>>> I stop and walk the bike somewhere safe, and check it out. Wheels
>>>> are well secured, steering column is tight, etc. I can't find
>>>> anything wrong. I ride it slow at first, no problems, and the later
>>>> I'm going down another hill (in a much safer place) and hit 30 mph
>>>> and no problems (but so ready to hit those brakes!)
>>>> It's a Giant OCR2 2003 or so -- aluminum frame, fork. It's pretty
>>>> much stock, except that it has 700x28c tires, and a luggage rack.
>>>> And interrupter brake handles, but I wasn't on the top part of the
>>>> bars this time. (This might be relevant -- I do most of my riding
>>>> with my hands on the top part of the bars. I don't race, I just
>>>> ride for exercise, fun and to get from point A to B.)
>>>> The bike is pretty new to me, but I'm not the first owner. I've
>>>> personally only got about 70 miles on it now. No problems like this
>>>> before, but this was probably the fastest I'd been on it until today
>>>> too.
>>>> This part of my ride makes me nervous, and so I might have been
>>>> holding on tighter than usual, but I doubt I was actually shaking
>>>> (well, I was after ...)
>>> You don't need to shake, although that can help initiate shimmy.
>>> Unless you hold onto the bars differently (loose grip) or can calm you
>>> response, you are reinforcing the natural frequency of bicycle shimmy.
>>> Generally the tighter you grip the bars the tenser your arm muscles
>>> are and worry about this occurring, the more certainly it will be
>>> initiated,
>>>> I've found a number of pages that talk about this --
>>> http://www.sheldonbrown.com/brandt/shimmy.html
>>> http://en.wikipedia.org/wiki/Speed_wobble
>>>> ... but I don't really know what to do about it. I was pretty
>>>> close to losing it, and if I had, it would have been very bad.
>>> First you must recognize that your natural response frequency is the
>>> same as the shimmy so even if you are not initiating it, you are
>>> reinforcing it.
>> jobst, he's a piece of floppy harmonic meat. he can't help reinforce it
>> if his dynamics coincide with that of the bike.
>>
>>
>>
>>>> One of the articles suggests putting a leg against my top tube,
>>>> which I'll try, but is there more that can be done? Something that
>>>> doesn't rely on me remembering to ride the right way?
>>> This should become natural to you. I think experimenting would help.
>>> Coast no-hands down a grade where this shimmy speed can be achieved
>>> and see whether it occurs. Then you will know what the natural
>>> critical speed is and know when to be prepared to suppress it.
>> that is a band-aid and does not fix the problem. worse, it doesn't
>> prevent it from starting, something a proper cure does.
>>
>>
>>
>>> That it occurs with hands on the bars makes me suspect you are not at
>>> ease at higher speeds. That is another solution.
>> typical - blame the rider.
>
> An age ago I was in a group coming down Gates Pass by Tucson, AZ, and
> a guy on a tall Colnago Super developed a shimmy. It was crazy; the
> rest of us were having a good time and this poor slob was almost
> wetting himself, thinking he was going to die. He blamed the bike.
> Said the headtube angle was too steep. Of course, this was the early
> 70s and there was a lot of voodoo in cycling. Now that we have Science
> all the voodoo is gone. Right?
>

apparently voodoo is alive and well if people think this is a problem
without a technical solution. farting about with one thigh stuck to the
frame is not exactly technical. and 70's colnagos had the old fashioned
slim diameter tubes that give more torsional flex, especially in larger
sizes.

 

[Ryan Cousineau]

In article
<c9d7726e-5d98-4e09-9313-3da9667a6ad3@g16g2000pri.googlegroups.com>,
[email protected] wrote:

> On Jun 13, 5:28 pm, "Mike Jacoubowsky" <[email protected]>
> wrote:
>
> [snip]
>
> > A bicycle isn't inherently stable; if it were, you
> > could give it a push and get it to head down the road a ways. In all cases
> > (with normal bikes) the bike is dependent upon rider input for stability.
> > Which is a problem, since a nervous rider does things that reinforce a
> > tendancy to shimmy. It's all in the FAQ, but I don't think the FAQ hits
> > hard
> > enough on the fact that a bicycle is inherently unstable until you add a
> > person to it. That should be enough to get people thinking in the right
>
> [snip]
>
> Dear Mike,
>
> Like you, I thought that a riderless bicycle was inherently unstable
> and would topple over shortly after being released.
>
> Several posters enjoyed setting me straight with movies like this:
>
> http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/bicycle_stability.mov

I don't think the first part was news to me, since I remember the
phenomenon of "ghost riding" bicycles as a kid, but the second part of
the video, where he slaps the saddle of the ghost-riding bike and it
RECOVERS was a bit of an eye-opener.

And that on a bike moving slowly enough that he was able to chase it
down in sandals,

--
Ryan Cousineau [email protected] http://www.wiredcola.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."

 

[Mike Jacoubowsky]

http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/bicycle_stability.mov

Wait a sec. You mean I have to take personal responsibility if I crash? It's
not my bike's fault?

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


<[email protected]> wrote in message
news:c9d7726e-5d98-4e09-9313-3da9667a6ad3@g16g2000pri.googlegroups.com...
On Jun 13, 5:28 pm, "Mike Jacoubowsky" <[email protected]>
wrote:

[snip]

> A bicycle isn't inherently stable; if it were, you
> could give it a push and get it to head down the road a ways. In all cases
> (with normal bikes) the bike is dependent upon rider input for stability.
> Which is a problem, since a nervous rider does things that reinforce a
> tendancy to shimmy. It's all in the FAQ, but I don't think the FAQ hits
> hard
> enough on the fact that a bicycle is inherently unstable until you add a
> person to it. That should be enough to get people thinking in the right

[snip]

Dear Mike,

Like you, I thought that a riderless bicycle was inherently unstable
and would topple over shortly after being released.

Several posters enjoyed setting me straight with movies like this:

http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/bicycle_stability.mov

Cheers,

Carl Fogel

 

[Colin Nelson]

<[email protected]> wrote in message
> news:c9d7726e-5d98-4e09-9313-3da9667a6ad3@g16g2000pri.googlegroups.com...
> On Jun 13, 5:28 pm, "Mike Jacoubowsky" <[email protected]>
> wrote:
>
> [snip]
>
> > A bicycle isn't inherently stable; if it were, you
> > could give it a push and get it to head down the road a ways. In all cases
> > (with normal bikes) the bike is dependent upon rider input for stability.
> > Which is a problem, since a nervous rider does things that reinforce a
> > tendancy to shimmy. It's all in the FAQ, but I don't think the FAQ hits
> > hard
> > enough on the fact that a bicycle is inherently unstable until you add a
> > person to it. That should be enough to get people thinking in the right
>
> [snip]
>
> Dear Mike,
>
> Like you, I thought that a riderless bicycle was inherently unstable
> and would topple over shortly after being released.
>
> Several posters enjoyed setting me straight with movies like this:
>
> http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/bicycle_stability.mov
>
> Cheers,
>
> Carl Fogel
>
>

Unable to see that site for some reason ... Is it the one where the forks were reversed? (but bikes need to negotiate bends as well as straights <wink>




--
Colin N.

Lincolnshire is mostly flat ... But the wind is mostly in your face

 

[[email protected]]

On Jun 13, 2:10 pm, "Doug McLaren" <dougmc
[email protected]> wrote:

> It's a Giant OCR2 2003 or so -- aluminum frame, fork.  It's pretty
> much stock, except that it has 700x28c tires, and a luggage rack.

What's on the rack, if anything? I've had floppy panniers cause a
seemingly intermittent wobble on a touring bike, at the beginning of a
tour in the Rockies. Cured 100% by wrapping spare bungee cords tight
around the rack and front packs, whose "shock cords" had rotted
internally, not obvious until used some and then they could be seen to
be "lumpy" and had suddenly lost all ability to hold tension. I
thought for sure it was the bike as this was the first trip on this
one, while the packs had been used in previous years, same general
riding area and conditions, but on a different frame, with no
problems. Spooky because there didn't seem to be a threshold speed
where the wobble would start, and no other obvious cause. --D-y

 

[[email protected]]

someone wrote:

>> It's a Giant OCR2 2003 or so -- aluminum frame, fork.  It's pretty
>> much stock, except that it has 700x28c tires, and a luggage rack.

I think there is still a misunderstanding about shimmy from this.
Shimmy is generated by gyroscopic steering effects of the rotating
front wheel and torsional compliance of the top- and downtube. The
rider mass firmly seated on the saddle and the front tire contact
patch is the axis about which the shimmy oscillates at a fairly fixed
rhythmic frequency. It is not an intermittent wobble or divergence.
Beyond that, when riding from a wet area onto dry pavement, the tire
track shows that its path is practically a straight line with
negligible lateral excursions.

> What's on the rack, if anything? I've had floppy panniers cause a
> seemingly intermittent wobble on a touring bike, at the beginning of
> a tour in the Rockies. Cured 100% by wrapping spare bungee cords
> tight around the rack and front packs, whose "shock cords" had
> rotted internally, not obvious until used some and then they could
> be seen to be "lumpy" and had suddenly lost all ability to hold
> tension. I thought for sure it was the bike as this was the first
> trip on this one, while the packs had been used in previous years,
> same general riding area and conditions, but on a different frame,
> with no problems. Spooky because there didn't seem to be a
> threshold speed where the wobble would start, and no other obvious
> cause.

Baggage, unless tight and solidly part of the bicycle frame, acts as a
damper. Beside that, it is not part of shimmy but can cause unsure
steering by shifting. Shimmy occurs at about 4Hz, something baggage
will not follow and therefore acts as a damper.

Jobst Brandt

 

[[email protected]]

On Sat, 14 Jun 2008 11:45:53 +0100, "Colin Nelson"
<[email protected]> wrote:

> <[email protected]> wrote in message
>> news:c9d7726e-5d98-4e09-9313-3da9667a6ad3@g16g2000pri.googlegroups.com...
>> On Jun 13, 5:28 pm, "Mike Jacoubowsky" <[email protected]>
>> wrote:
>>
>> [snip]
>>
>> > A bicycle isn't inherently stable; if it were, you
>> > could give it a push and get it to head down the road a ways. In all cases
>> > (with normal bikes) the bike is dependent upon rider input for stability.
>> > Which is a problem, since a nervous rider does things that reinforce a
>> > tendancy to shimmy. It's all in the FAQ, but I don't think the FAQ hits
>> > hard
>> > enough on the fact that a bicycle is inherently unstable until you add a
>> > person to it. That should be enough to get people thinking in the right
>>
>> [snip]
>>
>> Dear Mike,
>>
>> Like you, I thought that a riderless bicycle was inherently unstable
>> and would topple over shortly after being released.
>>
>> Several posters enjoyed setting me straight with movies like this:
>>
>> http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/bicycle_stability.mov
>>
>> Cheers,
>>
>> Carl Fogel
>>
>
>Unable to see that site for some reason ... Is it the one where the forks were reversed? (but bikes need to negotiate bends as well as straights <wink>

Dear Colin,

See if you can view a copy here:
http://home.comcast.net/~carlfogel/download/bicycle_stability.mov

It's a 2.5 mb QuickTime movie showing two runs of a riderless typical
bicycle, showing how stable it is

In the second run, the stupid bicycle recovers after a fellow running
next to bangs the seat to knock it sideways.

Cheers,

Carl Fogel

 

[[email protected]]

On Jun 14, 2:13 pm, [email protected] wrote:

> Baggage, unless tight and solidly part of the bicycle frame, acts as a
> damper.  Beside that, it is not part of shimmy but can cause unsure
> steering by shifting.  Shimmy occurs at about 4Hz, something baggage
> will not follow and therefore acts as a damper.

And that, ladies and gentlemen, is why my bike stopped wobbling when I
put the bags on securely. --D-y