High-speed shimmy, Speed wobble

wrote:

Shimmy only occurs
on conventional bicycles either when rider induced or while riding
no-hands.

I keep seeing you repeat this but I have never seen you substantiate it. And
it flies in the face of my experience.

And these aren't even two different categories. Riding no-hands qualifies
more as a rider-induced shimmy than does riding with your hands on the
handlebars. So in your world-view, all shimmies are rider induced:

1. Rider induces purposefully by removing hands
2. Rider induces purposefully by some hands-on technique
3. Rider induces inadvertently through fear or shivering or something.

Your position, stated in honest terms, is that "Shimmy only occurs on
conventional bicycles when rider induced." Your view is that the rider is
*always* the cause. Presumably failing to put ones knees against the top
tube is "causing" the bike to shimmy?

The truth of the matter is that shimmy is coming from some *undesirable*,
unpredictable harmonic oscillation. Bikes are not designed to shimmy; they
shimmy due to factors that are apparently beyond current design practices
to overcome without making undue compromises. I.e., the only way they know
how to fix the problem is to fiddle with components or hack the design by
adding dampeners.

The true cause is the complete system of bike and rider, *but the bicycle
designer's job is to account for the full range of reasonable rider
variations*. If the designer knows that some riders will be 150lbs, some
will be 220lbs, then the frame must withstand that range of weights. If he
knows that the rider may sit straight up, or lean almost over the
handlebars, then he must account for that. Likewise he must account for
various grips on the handlebars.

Perhaps what you mean to say, is that given the current state of the art, it
is the rider's *responsibility*, for the sake of his own safety, to be able
to respond correctly to shimmy. I agree with that. But saying it that way
instead of the way you put it leaves room for designers to have a healthy
frustration over the issue and not be complacent about it. It leaves room
for a clever engineer with his sights set on the problem to solve it
elegantly.

As an expert you should be doing what you can to encourage these kinds of
improvements, not providing rationalizations for the evasion of a definite
design problem.


Shayne Wissler

I would read Jobst's post to mean that if you have a shimmy caused by
resonant feedback that you often won't notice it when your hands on the
bars. They provide enough bracing to kill the vibrations. When you take
your hands off the bars, the system is free to vibrate and you get the
shimmy.

On Thu, 02 Oct 2003 23:15:07 +0000, Shayne Wissler wrote:

wrote:

Shimmy only occurs
on conventional bicycles either when rider induced or while riding
no-hands.

I keep seeing you repeat this but I have never seen you substantiate it. And
it flies in the face of my experience.

And these aren't even two different categories. Riding no-hands qualifies
more as a rider-induced shimmy than does riding with your hands on the
handlebars. So in your world-view, all shimmies are rider induced:

1. Rider induces purposefully by removing hands
2. Rider induces purposefully by some hands-on technique
3. Rider induces inadvertently through fear or shivering or something.

Your position, stated in honest terms, is that "Shimmy only occurs on
conventional bicycles when rider induced." Your view is that the rider is
*always* the cause. Presumably failing to put ones knees against the top
tube is "causing" the bike to shimmy?

The truth of the matter is that shimmy is coming from some *undesirable*,
unpredictable harmonic oscillation. Bikes are not designed to shimmy; they
shimmy due to factors that are apparently beyond current design practices
to overcome without making undue compromises. I.e., the only way they know
how to fix the problem is to fiddle with components or hack the design by
adding dampeners.

The true cause is the complete system of bike and rider, *but the bicycle
designer's job is to account for the full range of reasonable rider
variations*. If the designer knows that some riders will be 150lbs, some
will be 220lbs, then the frame must withstand that range of weights. If he
knows that the rider may sit straight up, or lean almost over the
handlebars, then he must account for that. Likewise he must account for
various grips on the handlebars.

Perhaps what you mean to say, is that given the current state of the art, it
is the rider's *responsibility*, for the sake of his own safety, to be able
to respond correctly to shimmy. I agree with that. But saying it that way
instead of the way you put it leaves room for designers to have a healthy
frustration over the issue and not be complacent about it. It leaves room
for a clever engineer with his sights set on the problem to solve it
elegantly.

As an expert you should be doing what you can to encourage these kinds of
improvements, not providing rationalizations for the evasion of a definite
design problem.


Shayne Wissler

--
Dick Schoeller

http://schoeller.ne.client2.attbi.com/
781.449.5476

"Er ist ein Narr, der meint, es sei nicht schad, das Kind
auszuschütten mit dem Bad" - Thomas Murner 1512

Shayne Wissler writes:

Shimmy only occurs on conventional bicycles either when rider
induced or while riding no-hands.

I keep seeing you repeat this but I have never seen you substantiate
it. And it flies in the face of my experience.

You are ignoring the examples I cite and the tests that I have done,
changing the weight and inflation pressure of the wheel, balancing and
unbalancing the wheel and riding over test courses to find what
interferes with shimmy buildup. All my road bicycles that I have
owned shimmied when allowed to do so by riding no-hands at the suitable
speed.

And these aren't even two different categories. Riding no-hands
qualifies more as a rider-induced shimmy than does riding with your
hands on the handlebars. So in your world-view, all shimmies are
rider induced:

1. Rider induces purposefully by removing hands
2. Rider induces purposefully by some hands-on technique
3. Rider induces inadvertently through fear or shivering or something.

That may be your interpretation, but riding no-hands is part of
bicycling, especially competitive bicycling where riders sit up to eat
and drink or change shirts while traveling at speeds that can induce
shimmy if allowed to occur. The constraint of always keeping hands on
the bars is unacceptable.

Your position, stated in honest terms, is that "Shimmy only occurs
on conventional bicycles when rider induced." Your view is that the
rider is *always* the cause. Presumably failing to put ones knees
against the top tube is "causing" the bike to shimmy?

That's your interpretation. When a coasting bicycle, with no rider
input, begins to shimmy is not rider induced in my perception. Rider
induced is when a rider has his hands on the bars and the bicycle
begins to shimmy. With the damping of hands and arms on the bars,
shimmy must be induced by an input from the rider. I have explained
how that occurs.

The truth of the matter is that shimmy is coming from some
*undesirable*, unpredictable harmonic oscillation. Bikes are not
designed to shimmy; they shimmy due to factors that are apparently
beyond current design practices to overcome without making undue
compromises. I.e., the only way they know how to fix the problem is
to fiddle with components or hack the design by adding dampeners.

As you may have noticed, it is not a serious problem and I have not
heard any people with whom I ride complain about it interfering with
their riding, safety or convenience. There are plenty of tall racers
whose bicycles will shimmy if given the opportunity. They never even
mention it. I have such a bicycle that will shimmy and can test
wheels whose makers claim they are shimmy resistant and show that they
are mistaken. My current bicycle has carried me over more than
200,000 miles on all sorts of roads and trails at speeds over 100km/h
without incident. It is NOT a problem.

The true cause is the complete system of bike and rider, *but the
bicycle designer's job is to account for the full range of
reasonable rider variations*. If the designer knows that some
riders will be 150lbs, some will be 220lbs, then the frame must
withstand that range of weights. If he knows that the rider may sit
straight up, or lean almost over the handlebars, then he must
account for that. Likewise he must account for various grips on the
handlebars.

I take it you want to write specifications for bicycle safety on
shimmy that you state you do not understand. I don't think that would
be a good project. On the other hand, when does your bicycle shimmy
and what have you done to understand it?

Perhaps what you mean to say, is that given the current state of the
art, it is the rider's *responsibility*, for the sake of his own
safety, to be able to respond correctly to shimmy. I agree with
that. But saying it that way instead of the way you put it leaves
room for designers to have a healthy frustration over the issue and
not be complacent about it. It leaves room for a clever engineer
with his sights set on the problem to solve it elegantly.

Do it!

As an expert you should be doing what you can to encourage these
kinds of improvements, not providing rationalizations for the
evasion of a definite design problem.

It's called "this kind of thing" or "these things", not both.

I'm waiting for someone, with better insights than I, to solve this.
From motor vehicles I see that they do not have a solution other than
steering dampers. With motor power, such devices are bearable. It's
so old that before I rode a motorcycle I heard of "tank slappers" and
"sun-fishing".

Jobst Brandt

Dick Schoeller wrote:

I would read Jobst's post to mean that if you have a shimmy caused by
resonant feedback that you often won't notice it when your hands on the
bars. They provide enough bracing to kill the vibrations. When you take
your hands off the bars, the system is free to vibrate and you get the
shimmy.

Well then there's a gross misunderstanding here on his part. That shimmies
of the character you refer to occur I have no doubt, but the type of shimmy
I experienced was violent. The front end of the bike jerked my hands back
and forth.

Since Brandt is stuck in his own dogmatic interpretations of shimmy based on
his own hacking around on a few bicycles, I know he's just going to say
that this doesn't happen unless the rider is somehow inducing it, but so
far he has presented no scientific basis for his position.


Shayne Wissler

As you may have noticed, it is not a serious problem and I have not
heard any people with whom I ride complain about it interfering with
their riding, safety or convenience. There are plenty of tall racers
whose bicycles will shimmy if given the opportunity. They never even
mention it. I have such a bicycle that will shimmy and can test
wheels whose makers claim they are shimmy resistant and show that they
are mistaken. My current bicycle has carried me over more than
200,000 miles on all sorts of roads and trails at speeds over 100km/h
without incident. It is NOT a problem.

nothing personal jobst, but i have to strongly disagree with you here.
my old 63cm frame shimmied so bad, it threw me and i broke a hip. i
don't call 8 weeks on crutches and 12 months of pain "not a problem".

i still have and still ride those wheels, and they /don't/ shimmy with
any of my new frames.

please mark me down as someone that /has/ mentioned it.

jb

wrote:

Shayne Wissler writes:

Shimmy only occurs on conventional bicycles either when rider
induced or while riding no-hands.

I keep seeing you repeat this but I have never seen you substantiate
it. And it flies in the face of my experience.

You are ignoring the examples I cite and the tests that I have done,

No, I'm just not allowing you to jump from "some" to "all" without a proper
reasoning process. You want to claim that your limited experience with a
few bicycles gives you a basis for having a universal knowledge of how all
bikes behave. This is a mistake children make all the time; I'm surprised
to catch you doing it.

The constraint of always keeping hands on the bars is unacceptable.

I agree.

Your position, stated in honest terms, is that "Shimmy only occurs
on conventional bicycles when rider induced." Your view is that the
rider is *always* the cause. Presumably failing to put ones knees
against the top tube is "causing" the bike to shimmy?

That's your interpretation. When a coasting bicycle, with no rider
input, begins to shimmy is not rider induced in my perception. Rider

That's my position.

induced is when a rider has his hands on the bars and the bicycle
begins to shimmy.

This is the point you have not provided any evidence for.

With the damping of hands and arms on the bars,
shimmy must be induced by an input from the rider. I have explained
how that occurs.

You are assuming that a bike cannot possibly have a resonance that is so
powerful that normal hand-dampening can't overcome it. You therefore
conclude that any shimmy while the hands are on the bike must have come
from the hands inducing it.

Again, you have no basis for this "cannot possibly" assumption other than
your own personal observations on a few bikes, combined with perhaps some
anecdotal evidence from a few friends and people you've met on the
internet.

Armed with this faulty assumption, you then brush aside any new evidence to
the contrary, using character attacks. As in when someone says "I didn't
induce that shimmy", you proceed to argue not on any scientific grounds,
nor do you ask for details and try to examine why such a thing would occur,
but instead you start making up stories about what this person must have
been doing (like he was scared or cold or something). You have no evidence
for any of these things; you're reasoning is purely circular, based on your
dogmatically-held premise.

The truth of the matter is that shimmy is coming from some
*undesirable*, unpredictable harmonic oscillation. Bikes are not
designed to shimmy; they shimmy due to factors that are apparently
beyond current design practices to overcome without making undue
compromises. I.e., the only way they know how to fix the problem is
to fiddle with components or hack the design by adding dampeners.

As you may have noticed, it is not a serious problem and I have not
heard any people with whom I ride complain about it interfering with
their riding, safety or convenience.

Again we see the faulty reasoning: no one in your little corner of the
universe experiences it, therefore it doesn't exist.

There are plenty of tall racers
whose bicycles will shimmy if given the opportunity. They never even
mention it. I have such a bicycle that will shimmy and can test
wheels whose makers claim they are shimmy resistant and show that they
are mistaken. My current bicycle has carried me over more than
200,000 miles on all sorts of roads and trails at speeds over 100km/h
without incident. It is NOT a problem.

More personal experiences being puffed up into specious generalizations.

The true cause is the complete system of bike and rider, *but the
bicycle designer's job is to account for the full range of
reasonable rider variations*. If the designer knows that some
riders will be 150lbs, some will be 220lbs, then the frame must
withstand that range of weights. If he knows that the rider may sit
straight up, or lean almost over the handlebars, then he must
account for that. Likewise he must account for various grips on the
handlebars.

I take it you want to write specifications for bicycle safety on
shimmy that you state you do not understand.

No, and I don't see how you came to that conclusion.

On the other hand, when does your bicycle shimmy
and what have you done to understand it?

I have noticed two shimmy modes, one similar to the one you describe which
is quite innocuous, and one that is violent. The former mode I don't really
care about, except for its possible connection to the latter. The latter
mode just barely presented itself, and I am in the process of trying to
understand it.

Perhaps what you mean to say, is that given the current state of the
art, it is the rider's *responsibility*, for the sake of his own
safety, to be able to respond correctly to shimmy. I agree with
that. But saying it that way instead of the way you put it leaves
room for designers to have a healthy frustration over the issue and
not be complacent about it. It leaves room for a clever engineer
with his sights set on the problem to solve it elegantly.

Do it!

Let's leave your Sunday School lessons out of this; they have little
relevance here.

As an expert you should be doing what you can to encourage these
kinds of improvements, not providing rationalizations for the
evasion of a definite design problem.

It's called "this kind of thing" or "these things", not both.

?

I'm waiting for someone, with better insights than I, to solve this.

Well this takes care of one half of my issue with what you've written. Now
if we can just get rid of those hasty generalizations.

From motor vehicles I see that they do not have a solution other than
steering dampers. With motor power, such devices are bearable. It's
so old that before I rode a motorcycle I heard of "tank slappers" and
"sun-fishing".

You might consider that with motor vehicles, there's not much motivation for
the elegant solution. Dampeners work, and they aren't a significant design
compromise, so why bother looking for any better solution? With bikes
dampeners are a huge compromise, so it's a huge mistake to make the
comparison you're making. It only leads to apathy toward the problem.


Shayne Wissler

Shayne Wissler writes:

You are assuming that a bike cannot possibly have a resonance that is so
powerful that normal hand-dampening can't overcome it. You therefore
conclude that any shimmy while the hands are on the bike must have come
from the hands inducing it.

Again, you have no basis for this "cannot possibly" assumption other than
your own personal observations on a few bikes, combined with perhaps some
anecdotal evidence from a few friends and people you've met on the
internet.

I'd add that Jobst mentioned recently that speeds under 30mph were all that is
needed to cause shimmy. I have a mild shimmy at around 18mph, which I could
ride with indefinitely, but the violent wobble I've experienced recently at
35-40mph (both with and without hands on the bars, but only unmanageable
with hands off) is entirely different.

It sounds like others who have experienced this violent shimmy mode also
encountered it well above 30mph. In my case I was neither cold nor scared
(well, not before the shimmy anyway), so I don't believe it was induced by the
rider.


Sam

Jim Beam writes:

As you may have noticed, it is not a serious problem and I have not
heard any people with whom I ride complain about it interfering with
their riding, safety or convenience. There are plenty of tall racers
whose bicycles will shimmy if given the opportunity. They never even
mention it. I have such a bicycle that will shimmy and can test
wheels whose makers claim they are shimmy resistant and show that they
are mistaken. My current bicycle has carried me over more than
200,000 miles on all sorts of roads and trails at speeds over 100km/h
without incident. It is NOT a problem.

Nothing personal Jobst, but I have to strongly disagree with you here.
My old 63cm frame shimmied so bad, it threw me and I broke a hip. I
don't call 8 weeks on crutches and 12 months of pain "not a problem".

I still have and still ride those wheels, and they /don't/ shimmy with
any of my new frames.

Please mark me down as someone that /has/ mentioned it.

That's not so easy, since I haven't ridden with you. I hope you saw
the qualification in the above paragraph. I don't deny that there are
folks who have fallen. It's just that there are people with different
skills.

Jobst Brandt

The true cause is the complete system of bike and rider, *but the bicycle
designer's job is to account for the full range of reasonable rider
variations*. If the designer knows that some riders will be 150lbs, some
will be 220lbs, then the frame must withstand that range of weights. If he
knows that the rider may sit straight up, or lean almost over the
handlebars, then he must account for that. Likewise he must account for
various grips on the handlebars.

[beware of personal anecdotes and ramblings to follow]

Can you design a frame that handles nicely around town at 15 miles per hour
as well as being stable at 40 miles per hour in a crosswind, *without*
taking rider handling & skills into account? How heavy would the frame need
to be? What other characteristics would accompany something so rigid that
any shimmy would occur in a frequency range not enhanced by the rider?

Manufacturers would love to do away with complaints about bike shimmy, for
reasons that this thread have made obvious. But to rehash what's already
been covered in this thread, it's a very frustrating issue because very few
riders ever experience it, and because it deals with a combination of rider
& bike.

The current thread is particularly interesting, because the shimmy didn't
appear until after the rider changed handlebar position. Thus we know that
the bike was originally stable, and have a darned good idea of how to bring
stability back to it. In other words, it's not a JRA (just riding along)
type of thing.

My main point is that there's been an implication in this thread that
manufacturers don't care or bother with this sort of thing, and that's
simply untrue. A lot of thought and care goes into designing a frame that's
inherently stable under nearly all conditions. It's in the manufacturer's
best interest to do so; the fear of lawsuits provides a powerful incentive
to manufacture something that's easily rideable.

My own experience comes from the real world (our customers), not a great
understanding of physics. And in that real world, we find that those rare
instances of shimmy are typically found with very large (59cm+) steel frames
*and* moderate-sized frames with very light riders. The big-frame guys
often find their shimmy issues solved, or at least greatly reduced, by going
to wider tires. I've found little correlation between changes in stem
length and shimmy although, curiously, height has been an issue (curiously
because that happens also to have been what may have initiated the shimmy in
this thread).

The really light rider on the 56cm frame in a crosswind? That's a tougher
one. Wider tires help, but that person is so light that a 28c tire, or even
25c, often seems inappropriate. I had one customer who we changed the fork
out several times (differing offsets and stiffness) with very little effect.
Once a crosswind hit her, it was all over. Different wheels, a bit better,
but not much. But once we got her on a bike with a very different position,
all was well. She wouldn't alter her position on the old bike, which made
it difficult to know for sure what "cured" the problem.

And on a personal observation, I've only had a shimmy issue once. I
remember it well- it was the Steinbeck Century in 1992, my very first ride
on a brand new 5200. I was descending Los Lorelas Grade (I might have
really botched the spelling!) from Carmel Valley to Highway 89, and at about
40 miles per hour developed quite a nasty wobble. Slowing down made it
better, but I wisely chose to simply stop, check the bike over, relax a bit
and then start back down the hill again. It absolutely, positively never
happened again. Obviously I changed something about my position on the bike
such that it didn't happen again, but I don't know exactly what. However, a
good many years of racing and getting myself into and out of very tight
situations may have helped; it's not as if I didn't know how to handle a
bike... most likely I made an almost automatic adjustment.to how I rode it.
Nothing new to me, just as I adapted between my two racing bikes in the
way-back days (a Cinelli and Bob Jackson with radically-different
geometries). Each one rode nicely, but very differently.

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


"Shayne Wissler" wrote in message
news:%j2fb.664762$Ho3.137294@sccrnsc03...
wrote:

Shimmy only occurs
on conventional bicycles either when rider induced or while riding
no-hands.

I keep seeing you repeat this but I have never seen you substantiate it.
And
it flies in the face of my experience.

And these aren't even two different categories. Riding no-hands qualifies
more as a rider-induced shimmy than does riding with your hands on the
handlebars. So in your world-view, all shimmies are rider induced:

1. Rider induces purposefully by removing hands
2. Rider induces purposefully by some hands-on technique
3. Rider induces inadvertently through fear or shivering or
something.

Your position, stated in honest terms, is that "Shimmy only occurs on
conventional bicycles when rider induced." Your view is that the rider is
*always* the cause. Presumably failing to put ones knees against the top
tube is "causing" the bike to shimmy?

The truth of the matter is that shimmy is coming from some *undesirable*,
unpredictable harmonic oscillation. Bikes are not designed to shimmy; they
shimmy due to factors that are apparently beyond current design practices
to overcome without making undue compromises. I.e., the only way they know
how to fix the problem is to fiddle with components or hack the design by
adding dampeners.

The true cause is the complete system of bike and rider, *but the bicycle
designer's job is to account for the full range of reasonable rider
variations*. If the designer knows that some riders will be 150lbs, some
will be 220lbs, then the frame must withstand that range of weights. If he
knows that the rider may sit straight up, or lean almost over the
handlebars, then he must account for that. Likewise he must account for
various grips on the handlebars.

Perhaps what you mean to say, is that given the current state of the art,
it
is the rider's *responsibility*, for the sake of his own safety, to be
able
to respond correctly to shimmy. I agree with that. But saying it that way
instead of the way you put it leaves room for designers to have a healthy
frustration over the issue and not be complacent about it. It leaves room
for a clever engineer with his sights set on the problem to solve it
elegantly.

As an expert you should be doing what you can to encourage these kinds of
improvements, not providing rationalizations for the evasion of a definite
design problem.


Shayne Wissler

wrote:

Jim Beam writes:

As you may have noticed, it is not a serious problem and I have not
heard any people with whom I ride complain about it interfering with
their riding, safety or convenience. There are plenty of tall racers
whose bicycles will shimmy if given the opportunity. They never even
mention it. I have such a bicycle that will shimmy and can test
wheels whose makers claim they are shimmy resistant and show that they
are mistaken. My current bicycle has carried me over more than
200,000 miles on all sorts of roads and trails at speeds over 100km/h
without incident. It is NOT a problem.

Nothing personal Jobst, but I have to strongly disagree with you here.
My old 63cm frame shimmied so bad, it threw me and I broke a hip. I
don't call 8 weeks on crutches and 12 months of pain "not a problem".

I still have and still ride those wheels, and they /don't/ shimmy with
any of my new frames.

Please mark me down as someone that /has/ mentioned it.

That's not so easy, since I haven't ridden with you.

Jobst, if you are going to restrict your universe to your own backyard,
don't give us these sweeping generalizations. Only a person who has
dilligently, honestly looked at *all* of the relevant data has a right to
such forms of expression.

I hope you saw
the qualification in the above paragraph. I don't deny that there are
folks who have fallen. It's just that there are people with different
skills.

At least your ad hominem is taking on a more subdued flavor. But it's still
ad hominem, and therefore still illogical. You have no reason to suspect
that Jim his a poor rider except that his experience contradicts your
apriori, hastily gotten, sweeping generalizations. You have not one iota of
evidence to accuse him of lack of skill. It's just a simplistic deduction
you're making from your tenaciously-held premise.


Shayne Wissler