wobble on fast curve?

I think my trimming of context may have misdirected you, Jim. It was
Callistus who claimed I must have been shaking/shivering like he
himself has experienced, and I think jobst was just trying to explain
what might have caused the shaking Callistus experienced. I see no
bullying ... although bullying might be a way to make a person start
shaking in their boots. ;-)

My apologies for causing the confusion,

Craig

Craig I ask you this question, not out of disrespect, but in order to
solve this problem. Like Hannibal Lector use to say, "Were you scared?"
Jobst is correct in that the "death grip" does make the problem worse.
What I try to do when the speed wobble occurs, is loosen up on the grip, as
light as I can get it. Sometimes this is hard to do, when all your weight
shifts from your ass to your hands as the descent steepens. I've tried
different positions, not to effect the shimmy, but to get the damn weight
off the hands. I think if you put some weight on the pedals, or put your
knees on the top tube, you push your body back so your hands arn't so heavy.
If you need a mechanical answer, try buying a wide 700x28 or 700x35
tire, and put it on the front wheel. You can get a tire from Nashbar like
that for $5-$10, so that's not much for experimentation purposes. Take it
to the hill where you know the bike will shimmy. Experiment, and you'll
find the answer. This is the most damning of all bicycle problems. Like
jobst said, there is plenty of old wives tales, that don't solve the
problem, but I think Jobst has a good take on it. My feeling is that rider
input, has more to do with it, than the bike.

Callistus Valerius wrote:
I think my trimming of context may have misdirected you, Jim. It was
Callistus who claimed I must have been shaking/shivering like he
himself has experienced, and I think jobst was just trying to explain
what might have caused the shaking Callistus experienced. I see no
bullying ... although bullying might be a way to make a person start
shaking in their boots. ;-)

My apologies for causing the confusion,

Craig


Craig I ask you this question, not out of disrespect, but in order to
solve this problem. Like Hannibal Lector use to say, "Were you scared?"
Jobst is correct in that the "death grip" does make the problem worse.
What I try to do when the speed wobble occurs, is loosen up on the grip, as
light as I can get it. Sometimes this is hard to do, when all your weight
shifts from your ass to your hands as the descent steepens. I've tried
different positions, not to effect the shimmy, but to get the damn weight
off the hands. I think if you put some weight on the pedals, or put your
knees on the top tube, you push your body back so your hands arn't so heavy.
If you need a mechanical answer, try buying a wide 700x28 or 700x35
tire, and put it on the front wheel. You can get a tire from Nashbar like
that for $5-$10, so that's not much for experimentation purposes. Take it
to the hill where you know the bike will shimmy. Experiment, and you'll
find the answer. This is the most damning of all bicycle problems. Like
jobst said, there is plenty of old wives tales, that don't solve the
problem, but I think Jobst has a good take on it. My feeling is that rider
input, has more to do with it, than the bike.


yes, a rider can "deal" with the problem, but with respect, you're
falling for the premise that's been bullied into people here over the
years - that the physical dynamics that cause the problem are
"acceptible" and therefore there's no point addressing them. jobst
doesn't think this is a serious issue because he has an old frame with
thicker walled tubes and old wheels with much less dish than modern
wheels. modern frames with thin walled tubes [of the old standard
diameter] and highly dished wheels are shimmy nightmares. shimmy can be
solved with bigger diameter tubes offering better torsonal stiffness and
wheels with better lateral stiffness [thicker drive side spokes, less
dish, stiffer rims, etc.]

the truth is, shimmy is no more an acceptible characteristic for a bike
than yaw instability on a plane. shimmy /is/ solvable. the right
frame/wheel combo /will/ give a bike on which shimmy does /not/ occur,
and the rider does /not/ have to accept this b.s. argument about this
very dangerous situation being /their/ lack of skill.

On Tue, 02 Aug 2005 01:24:12 -0400, CraigNJ
wrote:

On Mon, 01 Aug 2005 20:51:55 -0700, jim beam
wrote:

CraigNJ wrote:
On Tue, 02 Aug 2005 03:18:08 GMT, wrote:
Callistus Valerius writes:
... natural resonance of the muscles (that of shivering) ...
In my own case, I doubt that muscle shivering was involved. ...
i doubt it ever is.
fact: jobst has never tested ...
fact: jobst has never tested for ...
so, ... bullying - shivering!
...
jobst has quite astounding chutzpah.

I think my trimming of context may have misdirected you, Jim. It was
Callistus who claimed I must have been shaking/shivering like he
himself has experienced, and I think jobst was just trying to explain
what might have caused the shaking Callistus experienced. I see no
bullying ... although bullying might be a way to make a person start
shaking in their boots. ;-)

My apologies for causing the confusion,

My was that nicely put.

Jim Beam's hobby is following Jobst around and attempting to contradict,
criticize, gainsay and discredit his every utterance. Your post had essentially
nothing to do with it.

And yep, I've had the wobbles, both with and without benefit of that
biomechanical feedback loop discussed.

Ron

yes, a rider can "deal" with the problem, but with respect, you're
falling for the premise that's been bullied into people here over the
years - that the physical dynamics that cause the problem are
"acceptible" and therefore there's no point addressing them. jobst
doesn't think this is a serious issue because he has an old frame with
thicker walled tubes and old wheels with much less dish than modern
wheels. modern frames with thin walled tubes [of the old standard
diameter] and highly dished wheels are shimmy nightmares. shimmy can be
solved with bigger diameter tubes offering better torsonal stiffness and
wheels with better lateral stiffness [thicker drive side spokes, less
dish, stiffer rims, etc.]

the truth is, shimmy is no more an acceptible characteristic for a bike
than yaw instability on a plane. shimmy /is/ solvable. the right
frame/wheel combo /will/ give a bike on which shimmy does /not/ occur,
and the rider does /not/ have to accept this b.s. argument about this
very dangerous situation being /their/ lack of skill.

That's why the speed wobble is such a paradox. Jobst says the rider is
the dunce, you say the bike or wheel is a lemon. That is the paradox.
Solving it, is what is fun. As Hannibal would say "how did you
feel............when the wheel wobbled?" Tonight I will dine on lamb chops
with some fava beans and a nice Chianti, and think about speed wobbles.

On Tue, 02 Aug 2005 14:19:25 GMT, "Callistus Valerius"
wrote:

yes, a rider can "deal" with the problem, but with respect, you're
falling for the premise that's been bullied into people here over the
years - that the physical dynamics that cause the problem are
"acceptible" and therefore there's no point addressing them. jobst
doesn't think this is a serious issue because he has an old frame with
thicker walled tubes and old wheels with much less dish than modern
wheels. modern frames with thin walled tubes [of the old standard
diameter] and highly dished wheels are shimmy nightmares. shimmy can be
solved with bigger diameter tubes offering better torsonal stiffness and
wheels with better lateral stiffness [thicker drive side spokes, less
dish, stiffer rims, etc.]

the truth is, shimmy is no more an acceptible characteristic for a bike
than yaw instability on a plane. shimmy /is/ solvable. the right
frame/wheel combo /will/ give a bike on which shimmy does /not/ occur,
and the rider does /not/ have to accept this b.s. argument about this
very dangerous situation being /their/ lack of skill.

That's why the speed wobble is such a paradox. Jobst says the rider is
the dunce, you say the bike or wheel is a lemon. That is the paradox.
Solving it, is what is fun. As Hannibal would say "how did you
feel............when the wheel wobbled?" Tonight I will dine on lamb chops
with some fava beans and a nice Chianti, and think about speed wobbles.


Dear Cal,

Like you, I find the perennial shimmy questions fun.

Before you think about speed wobbles tonight, take a moment
and google for "motorcycle" and "shimmy"--something similar
can occur even when the rider-to-vehicle weight-ratio
changes wildly, the rider is sitting practically motionless
on a heavily padded seat, and the individual components
weigh more than an entire bicycle.

Carl Fogel

wrote: (clip) motorcycle (clip) shimmy (clip) can
occur even when the rider-to-vehicle weight-ratio changes wildly, the rider
is sitting practically motionless on a heavily padded seat, and the
individual components weigh more than an entire bicycle. (editing done for
brevity and clarity--not distortion.)
^^^^^^^^^^^^^^
We had a highway partolman who was badly injured because his Harley got in
to this mode. It can also appears as "shimmy" on cars with worn steering
linkage. It can occur on a trailer being towed with the wrong weight
distribution. It is a characteristic of any system in which negative
feedback changes to positive feedback for any of various reasons. It occurs
when an unfortunate combination of elasticity, mass, damping and control
forces occurs. What makes it hard to analyze on a bicycle is that the
components are not clear cut. A rider's arms have mass, which is coupled to
the steering, but not in an easily definable way. The riders arms also
respond dynamically to the problem, so they act like springs. The rider's
bodymass is planted on the seat, but the body is flexible, so only part of
it moves when the frame moves. And, of course, the bicycle itself has some
mass and elasticity.

When an oscillation is just starting, the natural tendency is for the rider
to stiffen his hold on the bar(s). This changes the dynamics, and probably
cures the problem in 99% of the cases, but occasionally it makes it worse.
If the rider then has the will and wisdom to lighten his grip, it may lessen
the oscillation, but, by then, the bike could be on the verge of crashing.

To elinate the wobble and keep from crashing, the rider has to change
something, but he usually doesn't know what. So change as many things as
you can. Slow down--turn and lean--grip the bike with your legs--shift your
weight. With some LUCK, you will move the operating point to a more stable
combination, and the wobble will subside.

balance front and rear ? the faster you go, the finer the required tune
throwing the front rear balance off during cornering or a hi speed run
over bumps that redistribute weightf/r
can start wobble in bearing races too loose or rims out of balance

the front wheel loses adhesion for a moment
and off you go
lean forward

On Tue, 2 Aug 2005 03:58:13 -0700, "Dale Benjamin"
wrote:
Did you have anything on a rack behind you?

No rack at all.

Thanks.

Craig

On 2 Aug 2005 13:29:16 -0700, wrote:


the front wheel loses adhesion for a moment
and off you go
lean forward

I was already leaning on my lower loop of my bars. Hmm, now there's
a thought -- if I was headed downhill with weight shifted to the
handlebars, maybe that lightened the rear enough for the rear (instead
of the front) to shimmy. (It felt more like it was happening to both
wheels, though I couldn't see it.) Hmmmm ... maybe that's what
happened, and if so, the cure would probably have been to shift my
weight back instead of forward.

Craig