Headshake causes and cures?

[bob prohaska's usenet account]

My elderly (small frame tube) Cannondale (bought used in the
late '80's) has always seemed a bit squirrely, and with narrow
(1.125") tires pumped up to 100 psi it will headshake gently
with no hands at 12-15 mph. The frequncy seems rather high,
somewhere between three and five hertz.

There are no obvious problems: The forks look straight, the steering
head bearings are neither loose nor binding, wheelbearings seem ok,
etc, etc.

I'd really like to be able to ride "hands off", at least for short
intervals, and wonder if this is a design characteristic or a hint
that something is amiss with the bicycle. In the past I blamed my
difficulties riding without hands on age and an impaired sense of
balance, but the headshake is clearly not related to either.

Thanks for reading, any counsel appreciated!

bob prohaska

[Mike Jacoubowsky]

> My elderly (small frame tube) Cannondale (bought used in the
> late '80's) has always seemed a bit squirrely, and with narrow
> (1.125") tires pumped up to 100 psi it will headshake gently
> with no hands at 12-15 mph. The frequncy seems rather high,
> somewhere between three and five hertz.

http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html

Just about everything you ever wanted to know about shimmy is in the faq.
Many people have tried to debunk it, but to the best of my knowledge, it
remains the definitive piece on what causes a bicycle to develop the shakes.

In general, shimmy is an inconvenience, not something that causes people to
actually crash. The fact that it occurs for your system (because it *is* a
system, comprised of both you and your bike... a different bike or a
different you changes things and may eliminate it) at a relatively-low speed
is probably less unusual than you think. People don't talk about shimmy much
in that speed range, but I think that's because they don't feel that it's as
scary at such speed, and certainly not as much fun to talk about. As in "Oh
yeah, you should have seen what it was like, flying down that hill at 47.632
mph when I sat up to put on my wind jacket and my bike went into this death
wobble..."

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


"bob prohaska's usenet account" > wrote in message
t...
> My elderly (small frame tube) Cannondale (bought used in the
> late '80's) has always seemed a bit squirrely, and with narrow
> (1.125") tires pumped up to 100 psi it will headshake gently
> with no hands at 12-15 mph. The frequncy seems rather high,
> somewhere between three and five hertz.
>
> There are no obvious problems: The forks look straight, the steering
> head bearings are neither loose nor binding, wheelbearings seem ok,
> etc, etc.
>
> I'd really like to be able to ride "hands off", at least for short
> intervals, and wonder if this is a design characteristic or a hint
> that something is amiss with the bicycle. In the past I blamed my
> difficulties riding without hands on age and an impaired sense of
> balance, but the headshake is clearly not related to either.
>
> Thanks for reading, any counsel appreciated!
>
> bob prohaska

[bob prohaska's usenet account]

Mike Jacoubowsky > wrote:
>
> Just about everything you ever wanted to know about shimmy is in the faq.

Well, not quite. I want to make it go away, and was looking for guidance
on things (hopefully specific to old Cannondales) that are plausible culprits.

>
> In general, shimmy is an inconvenience, not something that causes people to
> actually crash. The fact that it occurs for your system (because it *is* a
>
True, to a point. I've had the bike for close to twenty years, and it always
seemed the least competent component was the rider. Seeing it headshake no
hands at low speed made me realize there might be something wrong with the
bike. I'd gladly replace the fork if there was plausible reason to think
it would help.

bob prohaska


>

[Sandy]

Dans le message de t,
bob prohaska's usenet account > a réfléchi, et puis a
déclaré :
> My elderly (small frame tube) Cannondale (bought used in the
> late '80's) has always seemed a bit squirrely, and with narrow
> (1.125") tires pumped up to 100 psi it will headshake gently
> with no hands at 12-15 mph. The frequncy seems rather high,
> somewhere between three and five hertz.
>
> There are no obvious problems: The forks look straight, the steering
> head bearings are neither loose nor binding, wheelbearings seem ok,
> etc, etc.
>
> I'd really like to be able to ride "hands off", at least for short
> intervals, and wonder if this is a design characteristic or a hint
> that something is amiss with the bicycle. In the past I blamed my
> difficulties riding without hands on age and an impaired sense of
> balance, but the headshake is clearly not related to either.
>
> Thanks for reading, any counsel appreciated!
>
> bob prohaska

I had a C'dale of that vintage. There was a recall on forks, although it
didn't cover all models. I am sure C'dale could let you know if yours is
one of those affected. I am sorry I can't recall the details. Mine was
exchanged, and one of the problems solved was an ever-loosening headset.
Ask them, or maybe a long-time C'dale dealer.
--
Bonne route !

Sandy
Verneuil-sur-Seine FR

[[email protected]]

bob prohaska's usenet account wrote:
> My elderly (small frame tube) Cannondale (bought used in the late '80's)

How our perceptions have changed! :-) At the time we thought Cannondale
tubes were immensely oversized...

> has always seemed a bit squirrely, and with narrow
> (1.125") tires pumped up to 100 psi

Mountain bike?

The head tube angle on my mid-eighties Cannondale MTB measured out to
73 degrees at the local frame builder's shop. Catalog said 71 degrees,
and the stock Tange fork had rake similar to other brands also designed
with 71 degree head tube angles. Everyone who had ridden it said it
felt much quicker handling than other MTBs.

Not that steeper than designed head tube angles are a specific cause of
head shake, but it does change the steering response enough that if
other aspects of the system make it susceptible it might tip it in that
direction.

> it will headshake gently
> with no hands at 12-15 mph. The frequncy seems rather high,
> somewhere between three and five hertz.

Hm, that's lower than the 9 or 10 hertz I've experienced on flexible
road bikes. Maybe speed and frequency are related? Those were around
20+ mph.

> There are no obvious problems: The forks look straight, the steering
> head bearings are neither loose nor binding, wheelbearings seem ok,
> etc, etc.

Right, as the FAQ says these are usually not the problem.

> I'd really like to be able to ride "hands off", at least for short
> intervals, and wonder if this is a design characteristic or a hint
> that something is amiss with the bicycle.

Maybe both? I'd wonder about the head tube angle, for example, but
that's just based on my own experience. Normally Cannondales are quite
stiff, which reduces the tendency to wobble, and theoretically raises
the frequency to very high speeds. Maybe your frame's gotten more
fpexible due to a crack? But then you said it's always done it...

> In the past I blamed my
> difficulties riding without hands on age and an impaired sense of
> balance, but the headshake is clearly not related to either.
>
> Thanks for reading, any counsel appreciated!

The FAQ suggests two solutions: rest a leg on the top tube, or unweight
the saddle. Experiment to see if either of those help in your case?

[jim beam]

bob prohaska's usenet account wrote:
> My elderly (small frame tube) Cannondale (bought used in the
> late '80's) has always seemed a bit squirrely, and with narrow
> (1.125") tires pumped up to 100 psi it will headshake gently
> with no hands at 12-15 mph. The frequncy seems rather high,
> somewhere between three and five hertz.
>
> There are no obvious problems: The forks look straight, the steering
> head bearings are neither loose nor binding, wheelbearings seem ok,
> etc, etc.
>
> I'd really like to be able to ride "hands off", at least for short
> intervals, and wonder if this is a design characteristic or a hint
> that something is amiss with the bicycle. In the past I blamed my
> difficulties riding without hands on age and an impaired sense of
> balance, but the headshake is clearly not related to either.
>
> Thanks for reading, any counsel appreciated!
>
> bob prohaska

what rear wheel do you have?

from what i can see, shimmy is the result of two factors: torsional flex
in the frame and lateral flex in the wheels, which really means the rear
wheel since it's dished, and /much/ more flexible on the drive side due
to the reduced bracing angle. together, if they happen to have
resonance in the same frequency range, you get shimmy. if the resonance
of the two can be "tuned" away from each other, the shimmy goes away.
[assuming you don't have something a loose headset or a broken axle of
course.]

using that info, i substantially mitigated a similar problem on a
shimmy-prone frame with a stiffer rear wheel. i used a dura-ace hub
[greatest flange offset] and plain gauge spokes [the most inelastic],
and it worked well. the original wheels worked fine in other frames.
this frame worked well with the stiffer rear. ultimately though,
replacing that frame with a [torsionally stiffer] big tube model has
given me an unconditionally stable, much more enjoyable ride.

riding with one leg on the top tube is definitely not a "cure". as you
seem to realize, it's a design characteristic, which thankfully, seems
to be recognized my many [but still not all] modern manufacturers.

[bob prohaska's usenet account]

wrote:
> bob prohaska's usenet account wrote:
>> My elderly (small frame tube) Cannondale (bought used in the late '80's)
>
> How our perceptions have changed! :-) At the time we thought Cannondale
> tubes were immensely oversized...

Actually, this one looks fairly normal; maybe a little fatter than old
steel-framed bikes, but nothing like the later incarnations.

>
> Mountain bike?
>
Quite the opposite; a roadbike with drop bars and downtube shifters.
Not being quite so athletic & coordinated I added thumb shifters and
Scott MTB handlebars along with (until now) fatter tires, usually
1.375" wide.

> The head tube angle on my mid-eighties Cannondale MTB measured out to
> 73 degrees at the local frame builder's shop. Catalog said 71 degrees,
> and the stock Tange fork had rake similar to other brands also designed
> with 71 degree head tube angles. Everyone who had ridden it said it
> felt much quicker handling than other MTBs.
>

> Not that steeper than designed head tube angles are a specific cause of
> head shake, but it does change the steering response enough that if
> other aspects of the system make it susceptible it might tip it in that
> direction.
>

Steeper head angles make for less stable steering, certainly.
Sounds like maybe this is just an inherently lively frame. That's
the sort of clue I was looking for; nothing to fix, just live with
it or change it. For now I'll live with it.

Thanks!

bob prohaska

[bob prohaska's usenet account]

jim beam > wrote:
>
> what rear wheel do you have?
>
It's the OEM Wolber 27", original hub & spokes.

bob prohaska

[jim beam]

bob prohaska's usenet account wrote:
> jim beam > wrote:
>
>>what rear wheel do you have?
>>
>
> It's the OEM Wolber 27", original hub & spokes.
>
> bob prohaska
>
so it's been like this since new?

[Peter Cole]

bob prohaska's usenet account wrote:
> wrote:
>> bob prohaska's usenet account wrote:
>>> My elderly (small frame tube) Cannondale (bought used in the late '80's)
>> How our perceptions have changed! :-) At the time we thought Cannondale
>> tubes were immensely oversized...
>
> Actually, this one looks fairly normal; maybe a little fatter than old
> steel-framed bikes, but nothing like the later incarnations.

That may be the problem. The frame may have poor torsional stiffness. Is
it a large frame?

[bob prohaska's usenet account]

jim beam > wrote:
> so it's been like this since new?

Certainly for the ~20 years I've had it. The fact that
I could not ride the bike "no hands" annoyed me a bit,
having memories as a kid of riding without hands for
minutes at a stretch. But that was then, this was many
years later. I looked at the bike carefully searching
for mechanical damage like bent forks, but could find
nothing wrong and eventually attributed my inability
to ride without hands to simply getting older.

When the bike exhibited headshake with high pressure
tires the thought dawned that maybe something was in
fact wrong with the bike, based on experience with
similar problems on motorcycles that did eventually
trace back to mechanical problems (in that case it
turned out to be bad steering head bearings).

I'm interpreting the headshake as a bug; maybe it's
just a feature 8-) The bicycle has given good service,
at least for a rider of my abilities.

thanks for reading,

bob prohaska

[jim beam]

bob prohaska's usenet account wrote:
> jim beam > wrote:
>
>>so it's been like this since new?
>
>
> Certainly for the ~20 years I've had it. The fact that
> I could not ride the bike "no hands" annoyed me a bit,
> having memories as a kid of riding without hands for
> minutes at a stretch. But that was then, this was many
> years later. I looked at the bike carefully searching
> for mechanical damage like bent forks, but could find
> nothing wrong and eventually attributed my inability
> to ride without hands to simply getting older.
>
> When the bike exhibited headshake with high pressure
> tires the thought dawned that maybe something was in
> fact wrong with the bike, based on experience with
> similar problems on motorcycles that did eventually
> trace back to mechanical problems (in that case it
> turned out to be bad steering head bearings).
>
> I'm interpreting the headshake as a bug; maybe it's
> just a feature 8-) The bicycle has given good service,
> at least for a rider of my abilities.
>
> thanks for reading,
>
> bob prohaska

well, whether you want to live with it is your choice. the ultimate
cure is replacement with a big tubed frame as mentioned before. but the
stiffer wheel trick will definitely be an improvement. just rebuild the
rear with 2.0mm plain gauge spokes on the drive side and re-use
everything else.

[bob prohaska's usenet account]

jim beam > wrote:
> well, whether you want to live with it is your choice. the ultimate
> cure is replacement with a big tubed frame as mentioned before. but the

Would you attribute the improvement to the stiffer construction of the
big tubed frame, or the difference in steering head angle?

> stiffer wheel trick will definitely be an improvement. just rebuild the
> rear with 2.0mm plain gauge spokes on the drive side and re-use
> everything else.

I've toyed with the idea of going to modern rim sizes; 27 inch is fairly
ancient nowadays. Perhaps I should consider a new (extra) wheelset. It
would certainly offer a clean comparison. It's hard for me to believe
that the rear wheel is the culprit, but I admit strange things happen.

Thanks for your counsel!

bob prohaska

[jim beam]

bob prohaska's usenet account wrote:
> jim beam > wrote:
>
>>well, whether you want to live with it is your choice. the ultimate
>>cure is replacement with a big tubed frame as mentioned before. but the
>
>
> Would you attribute the improvement to the stiffer construction of the
> big tubed frame, or the difference in steering head angle?

angle [trail], etc. affects the amount of "correction" [input] force the
system experiences, but it doesn't affect frequency. that's the result
of the spring constants of the components and their masses. some bikes
may be more prone to shimmy as a result of differences in trail, but
imo, if a bike can easily be deliberately /induced/ to shimmy, it's
going to happen when you don't want it to as well. i had a crash a few
years back as a result of sudden shimmy onset, and i had neither the
time nor balance to do anything about it. i cracked my hip and was in
pain for about a year. sure, shimmy can be "controlled", but i don't
think the rider should have to. especially as the cure is so simple and
costs no more at the frame manufacturing stage.

>
>
>>stiffer wheel trick will definitely be an improvement. just rebuild the
>>rear with 2.0mm plain gauge spokes on the drive side and re-use
>>everything else.
>
>
> I've toyed with the idea of going to modern rim sizes; 27 inch is fairly
> ancient nowadays. Perhaps I should consider a new (extra) wheelset. It
> would certainly offer a clean comparison. It's hard for me to believe
> that the rear wheel is the culprit, but I admit strange things happen.

take the rear wheel out and place it with the axle on a wooden block.
then press with both hands in opposite placed gently downward. with the
gear side down, the wheel will be impressively rigid. but gear side up,
it will flex to the point where the non-drive side spokes go completely
slack - with ease. thicker spokes [and stiffer rim] mitigate that to a
good degree. of the two components, frame or wheel, the latter is by
far the cheaper and simpler to address.

>
> Thanks for your counsel!
>
> bob prohaska
>

[[email protected]]

Southern Comfort writes:

>>> well, whether you want to live with it is your choice. the
>>> ultimate cure is replacement with a big tubed frame as mentioned
>>> before. but the stiffer wheel trick will definitely be an
>>> improvement. just rebuild the rear with 2.0mm plain gauge spokes
>>> on the drive side and re-use everything else.

>> Would you attribute the improvement to the stiffer construction of
>> the big tubed frame, or the difference in steering head angle?

> angle [trail], etc. affects the amount of "correction" [input] force
> the system experiences, but it doesn't affect frequency. that's the
> result of the spring constants of the components and their masses.
> some bikes may be more prone to shimmy as a result of differences in
> trail, but imo, if a bike can easily be deliberately /induced/ to
> shimmy, it's going to happen when you don't want it to as well. i
> had a crash a few years back as a result of sudden shimmy onset, and
> i had neither the time nor balance to do anything about it. i
> cracked my hip and was in pain for about a year. sure, shimmy can
> be "controlled", but i don't think the rider should have to.
> especially as the cure is so simple and costs no more at the frame
> manufacturing stage.

From this I take it your hands were on the bars. If that is correct,
then you were the cause of the shimmy. I think this has been hashed
over enough on this forum and tested by riders including Damon Rinard
who performed instrumented shimmy tests of different wheels for TREK.

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

>> I've toyed with the idea of going to modern rim sizes; 27 inch is
>> fairly ancient nowadays. Perhaps I should consider a new (extra)
>> wheelset. It would certainly offer a clean comparison. It's hard
>> for me to believe that the rear wheel is the culprit, but I admit
>> strange things happen.

> take the rear wheel out and place it with the axle on a wooden
> block. then press with both hands in opposite placed gently
> downward. with the gear side down, the wheel will be impressively
> rigid. but gear side up, it will flex to the point where the
> non-drive side spokes go completely slack - with ease. thicker
> spokes [and stiffer rim] mitigate that to a good degree. of the two
> components, frame or wheel, the latter is by far the cheaper and
> simpler to address.

What evidence do you have that the rear wheel is the source of this
instability?

Jobst Brandt

[Tim McNamara]

In article >,
wrote:

> From this I take it your hands were on the bars. If that is correct,
> then you were the cause of the shimmy.

A tremor of about 7 Hz is a physiologically normal part of human motor
functioning. Photographers are very familiar with this fact, which is
why they use tripods in circumstances where tremor could spoil the
photo. It's also a well-known concern for surgeons. There is some
variability, of course, but the research I've looked at this morning
makes me winder if some people are not more prone to experiencing bike
shimmy due to their basically normal neuromuscular functioning. The
abstracts from two studies are copied below. Note that in the second
abstract, the forces involved can become quite large (0.2 to 7 kg).

Arch Neurol. 1982 Jun;39(6):358-62. Related Articles, Links

A normative study of postural tremor of the hand.

Wade P, Gresty MA, Findley LJ.

In a normative study of amplitude, frequency, and variability of
postural tremor of the hand in 97 normal subjects, 15 to 80 years old,
tremor was transduced using accelerometers and characterized by power
spectral analysis. Tremor amplitude ranged from a 0.0015- to 0.035-g
peak at the dominant frequency. The modal tremor amplitude was 0.01-g
peak, and the threshold for "visible tremor" was 0.007-g peak. The modal
tremor frequency was constant at about 7 Hz in those subjects up to 70
years old and thereafter decreased to about 6 Hz. The mean range of
variability of the dominant frequency was 2.5 Hz. The tremor pattern,
characterized by the shape of spectra, varied greatly from a single
finely tuned peak to multiple broad peaks. More than two thirds of
normal subjects showed complex spectral patterns with more than one peak
of significance. Passive resonance of the hand tissues was an important
factor in determining dominant tremor frequencies in most subjects. Many
subjects showed a strong, albeit variable , cardioballistic component.
The results provide baseline data for studies of the effects of drugs on
tremor, particularly in cases of "essential" tremor, and provide
warnings that such studies require objective recording methods for
adequate evaluation and need recourse to measurement of several factors
of the tremor to elucidate the component of tremor affected by a drug. A
scaling of tremor can be used in terms of reference to the strength of
gravitational acceleration (1.0 g), which provides simple numerical
relationships.

J Neurophysiol. 1978 May;41(3):557-71.

Neuronal mechanisms underlying physiological tremor.

Allum JH, Dietz V, Freund HJ.

1. Tremor force was recorded during stationary isometric
contractions of intrinsic hand muscles of normal subjects. Subjects
maintained a steady force level between their thumb and forefinger for
30 s. The force level varied from weak (0.2 kg) to strong contractions
(7 kg). These experimental conditions were the same as those in two
preceding studies, where single motor-unit activity (14) and the
correlation between the discharges of two simultaneously recorded motor
units and physiological tremor (11) have been investigated. 2. Two
alterations of the power spectra were observed at successively stronger
contractions: increase of tremor amplitude and changes in the shape of
the power spectrum. At all force levels, the power spectra of tremor
force show the well-known decay of tremor amplitude from the lower to
the higher frequencies with a local peak at 6--10 Hz. This peak does not
show a significant change with respect to frequency when the force level
is varied. It is shifted toward lower frequencies in a pathological
condition (Parkinsonism) where the recruitment firing rates of the motor
units are significantly lower than in the normal. 3. Higher frequencies
(greater than 20 Hz) are barely present in the power spectrum during the
very weak contractions. They become significant as the contractions
become stronger. 4. The steep decay of the power spectrum toward higher
frequencies has a similar slope (--43 dB/decade) as the reduction in
amplitude of the unfused part of the muscle contractions with increasing
stimulus rates (--38 dB/decade). The cutoff of the power spectrum above
25 Hz parallels the achievement of total fusion of muscle twitches above
this rate. 5. The results are consistent with the hypothesis that the
power spectrum over the range of 6--25 Hz is mainly caused by the
unfused parts of the twitch contractions of motor units firing between
recruitment (6--8/s) and total fusion of the twitches (25--30/s). The
decline of the power spectrum toward higher frequencies can be explained
by mechanical damping, which results from increasing fusion of the
twitch contractions. The low-frequency part of the power spectrum is
assumed to be the result of the slow force deviations produced by
changes in the net output of the motoneuron pool.

[Michael Press]

In article
>,
Tim McNamara > wrote:

> In article >,
> wrote:
>
> > From this I take it your hands were on the bars. If that is correct,
> > then you were the cause of the shimmy.
>
> A tremor of about 7 Hz is a physiologically normal part of human motor
> functioning. Photographers are very familiar with this fact, which is
> why they use tripods in circumstances where tremor could spoil the
> photo. It's also a well-known concern for surgeons. There is some
> variability, of course, but the research I've looked at this morning
> makes me winder if some people are not more prone to experiencing bike
> shimmy due to their basically normal neuromuscular functioning. The
> abstracts from two studies are copied below. Note that in the second
> abstract, the forces involved can become quite large (0.2 to 7 kg).
>
> Arch Neurol. 1982 Jun;39(6):358-62. Related Articles, Links
>
> A normative study of postural tremor of the hand.
>
> Wade P, Gresty MA, Findley LJ.
>
> In a normative study of amplitude, frequency, and variability of
> postural tremor of the hand in 97 normal subjects, 15 to 80 years old,
> tremor was transduced using accelerometers and characterized by power
> spectral analysis. Tremor amplitude ranged from a 0.0015- to 0.035-g
> peak at the dominant frequency. The modal tremor amplitude was 0.01-g
> peak, and the threshold for "visible tremor" was 0.007-g peak. The modal
> tremor frequency was constant at about 7 Hz in those subjects up to 70
> years old and thereafter decreased to about 6 Hz. The mean range of
> variability of the dominant frequency was 2.5 Hz. The tremor pattern,
> characterized by the shape of spectra, varied greatly from a single
> finely tuned peak to multiple broad peaks. More than two thirds of
> normal subjects showed complex spectral patterns with more than one peak
> of significance. Passive resonance of the hand tissues was an important
> factor in determining dominant tremor frequencies in most subjects. Many
> subjects showed a strong, albeit variable , cardioballistic component.
> The results provide baseline data for studies of the effects of drugs on
> tremor, particularly in cases of "essential" tremor, and provide
> warnings that such studies require objective recording methods for
> adequate evaluation and need recourse to measurement of several factors
> of the tremor to elucidate the component of tremor affected by a drug. A
> scaling of tremor can be used in terms of reference to the strength of
> gravitational acceleration (1.0 g), which provides simple numerical
> relationships.

[...]

This 7 Hz tremor is the how we generate heat to maintain
our core body temperature. Shivering evolves when the
normal amplitude tremor generates insufficient heat.

One sign of good muscle tone is the ability to produce
large quantities of heat in a resting state. For instance,
surfers are entirely comfortable wandering around northern
California beaches at night in shorts, and maybe a
tee-shirt.

Long ago I read that when feeling slightly chilled one
should not shrink from the cold but to go out and meet the
cold. This visualization works, and works better the more
it is used. It is an exercise that transforms oneself into
an effective heat generating machine.

--
Michael Press

[Tim McNamara]

In article >,
Michael Press > wrote:

> In article >,
> Tim McNamara > wrote:
>
> > In article >,
> > wrote:
> >
> > > From this I take it your hands were on the bars. If that is
> > > correct, then you were the cause of the shimmy.
> >
> > A tremor of about 7 Hz is a physiologically normal part of human
> > motor functioning. Photographers are very familiar with this fact,
> > which is why they use tripods in circumstances where tremor could
> > spoil the photo. It's also a well-known concern for surgeons.
> > There is some variability, of course, but the research I've looked
> > at this morning makes me winder if some people are not more prone
> > to experiencing bike shimmy due to their basically normal
> > neuromuscular functioning. The abstracts from two studies are
> > copied below. Note that in the second abstract, the forces
> > involved can become quite large (0.2 to 7 kg).

<snip cites>

> This 7 Hz tremor is the how we generate heat to maintain our core
> body temperature. Shivering evolves when the normal amplitude tremor
> generates insufficient heat.

A few years back a buddy of mine and I rode a 400 km brevet together.
The temps dropped much lower than predicted (prediction was mid 50s F
and we saw 28 F on a bank time & temp display, but who knows how
accurate that was. Nothing was obviously freezing except us). We were
much underdressed, my friend more so than me. We left the Chatffield MN
control somewhere around midnight and he was shaking from the cold so
badly that he had a serious "speed wobble" going uphill at 10 mph! He
was probably in the early stages of hypothermia. The climb warmed us
up, and out of the valley onto the plateau the air was much much warmer.
We finished the rest of the ride in relative comfort with the addition
of a layer of newspaper under the fronts of our jerseys.

[[email protected]]

Tim McNamara writes:

>>>> From this I take it your hands were on the bars. If that is
>>>> correct, then you were the cause of the shimmy.

>>> A tremor of about 7 Hz is a physiologically normal part of human
>>> motor functioning. Photographers are very familiar with this
>>> fact, which is why they use tripods in circumstances where tremor
>>> could spoil the photo. It's also a well-known concern for
>>> surgeons. There is some variability, of course, but the research
>>> I've looked at this morning makes me winder if some people are not
>>> more prone to experiencing bike shimmy due to their basically
>>> normal neuromuscular functioning. The abstracts from two studies
>>> are copied below. Note that in the second abstract, the forces
>>> involved can become quite large (0.2 to 7 kg).

> <snip cites>

>> This 7 Hz tremor is the how we generate heat to maintain our core
>> body temperature. Shivering evolves when the normal amplitude
>> tremor generates insufficient heat.

> A few years back a friend and I rode a 400 km brevet. The
> temperature dropped much lower than predicted (prediction was mid
> 50s F) and we saw 28 F on a bank time & temp display, but who knows
> how accurate that was. We were much under dressed, my friend more
> so than I. As we left the Chatfield MN control somewhere around
> midnight, he was shaking from the cold so badly that he had a
> serious "speed wobble" going uphill at 10 mph! He was probably in
> the early stages of hypothermia. The climb warmed us up, and out of
> the valley onto the plateau the air was much much warmer. We
> finished the rest of the ride in relative comfort with the addition
> of a layer of newspaper under the fronts of our jerseys.

That is similar to the experience I had years ago and now and then
since. That's what made the hands-on shimmy problem apparent to me.

Jobst Brandt

[jim beam]

wrote:
> Southern Comfort writes:
>
>
>>>>well, whether you want to live with it is your choice. the
>>>>ultimate cure is replacement with a big tubed frame as mentioned
>>>>before. but the stiffer wheel trick will definitely be an
>>>>improvement. just rebuild the rear with 2.0mm plain gauge spokes
>>>>on the drive side and re-use everything else.
>
>
>>>Would you attribute the improvement to the stiffer construction of
>>>the big tubed frame, or the difference in steering head angle?
>
>
>>angle [trail], etc. affects the amount of "correction" [input] force
>>the system experiences, but it doesn't affect frequency. that's the
>>result of the spring constants of the components and their masses.
>>some bikes may be more prone to shimmy as a result of differences in
>>trail, but imo, if a bike can easily be deliberately /induced/ to
>>shimmy, it's going to happen when you don't want it to as well. i
>>had a crash a few years back as a result of sudden shimmy onset, and
>>i had neither the time nor balance to do anything about it. i
>>cracked my hip and was in pain for about a year. sure, shimmy can
>>be "controlled", but i don't think the rider should have to.
>>especially as the cure is so simple and costs no more at the frame
>>manufacturing stage.
>
>
> From this I take it your hands were on the bars. If that is correct,
> then you were the cause of the shimmy.

no, hands off.

> I think this has been hashed
> over enough on this forum and tested by riders including Damon Rinard
> who performed instrumented shimmy tests of different wheels for TREK.

so how exactly did this testing determine that the rider is the cause? i
say this is merely typical jobstian speculative guesswork. if it were
true, all my bikes would shimmy. they don't.

and if a bike has a shimmy frequency the same as /any/ form of
induction, and that shimmy can reach sufficient amplitude to throw a
rider, it's a problem that needs to be properly dealt with. this
ridiculous attitude of "it's the riders fault so let's not bother
dealing with it" is just stupid beyond belief. especially when it's so
easily fixed.

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

propagation of your baseless unscientific drivellings are a massive
negative for the credibility of the bike industry.

>
>
>>>I've toyed with the idea of going to modern rim sizes; 27 inch is
>>>fairly ancient nowadays. Perhaps I should consider a new (extra)
>>>wheelset. It would certainly offer a clean comparison. It's hard
>>>for me to believe that the rear wheel is the culprit, but I admit
>>>strange things happen.
>
>
>>take the rear wheel out and place it with the axle on a wooden
>>block. then press with both hands in opposite placed gently
>>downward. with the gear side down, the wheel will be impressively
>>rigid. but gear side up, it will flex to the point where the
>>non-drive side spokes go completely slack - with ease. thicker
>>spokes [and stiffer rim] mitigate that to a good degree. of the two
>>components, frame or wheel, the latter is by far the cheaper and
>>simpler to address.
>
>
> What evidence do you have that the rear wheel is the source of this
> instability?

because the stiffer wheel stopped it. resonance is a function of both
mass and spring constant. remember?

>
> Jobst Brandt

[bob prohaska's usenet account]

wrote:
>
> That is similar to the experience I had years ago and now and then
> since. That's what made the hands-on shimmy problem apparent to me.

If you'll forgive me for trying to steal back the thread, what's the
story with hands _off_ shimmy? Basically I'm asking if this is apt to
be a correctable problem (as suggested by the rear wheel stiffness
argument) or an inherently inalterable property of the frame.

I'm not opposed to changing wheels or forks, but don't want to make
the investment only to discover it's a frame problem.

On motorcycles one can usually settle steering somewhat by extending
forks, putting on a larger front tire and/or a smaller rear tire.
Wider tires tend also to stabilize things, provided the profile is
appropriate (semicircular rather than vee'd). But, motorcycles are
an order of magnitude heavier: Do such changes have appreciable effect
on bicycles?

Thanks for reading!
bob prohaska

>

[[email protected]]

Johnnie Walker writes:

>>>>> well, whether you want to live with it is your choice. the
>>>>> ultimate cure is replacement with a big tubed frame as mentioned
>>>>> before. but the stiffer wheel trick will definitely be an
>>>>> improvement. just rebuild the rear with 2.0mm plain gauge
>>>>> spokes on the drive side and re-use everything else.

>>>> Would you attribute the improvement to the stiffer construction
>>>> of the big tubed frame, or the difference in steering head angle?

>>> angle [trail], etc. affects the amount of "correction" [input]
>>> force the system experiences, but it doesn't affect frequency.
>>> that's the result of the spring constants of the components and
>>> their masses. some bikes may be more prone to shimmy as a result
>>> of differences in trail, but imo, if a bike can easily be
>>> deliberately /induced/ to shimmy, it's going to happen when you
>>> don't want it to as well. i had a crash a few years back as a
>>> result of sudden shimmy onset, and i had neither the time nor
>>> balance to do anything about it. i cracked my hip and was in pain
>>> for about a year. sure, shimmy can be "controlled", but i don't
>>> think the rider should have to. especially as the cure is so
>>> simple and costs no more at the frame manufacturing stage.

>> From this I take it your hands were on the bars. If that is
>> correct, then you were the cause of the shimmy.

> no, hands off.

The why didn't you put your hands on the bars and stop it. It takes a
bit of time to build up to a hazardous level. Besides, as you reached
for the bars you could have damped the whole thing out with the leg
against the top tube.

>> I think this has been hashed over enough on this forum and tested
>> by riders including Damon Rinard who performed instrumented shimmy
>> tests of different wheels for TREK.

> so how exactly did this testing determine that the rider is the
> cause? i say this is merely typical jobstian speculative guesswork.
> if it were true, all my bikes would shimmy. they don't.

If you didn't have your hands on the bars you logically would have
taken the effort to put them there rather than watch the effect
snowball into a crash. Therefore, it is reasonable to assume you had
your hands on the bars.

> and if a bike has a shimmy frequency the same as /any/ form of
> induction, and that shimmy can reach sufficient amplitude to throw a
> rider, it's a problem that needs to be properly dealt with. this
> ridiculous attitude of "it's the riders fault so let's not bother
> dealing with it" is just stupid beyond belief. especially when it's
> so easily fixed.

Well, it might throw a novice rider who has never experienced this. I
assumed you had enough experience, from all the things you write about
here to not be one of those.

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

> propagation of your baseless unscientific drivellings are a massive
> negative for the credibility of the bike industry.

You'll have to show more than hyperbole to discount what I wrote on
the subject.

>>>> I've toyed with the idea of going to modern rim sizes; 27 inch is
>>>> fairly ancient nowadays. Perhaps I should consider a new (extra)
>>>> wheelset. It would certainly offer a clean comparison. It's
>>>> hard for me to believe that the rear wheel is the culprit, but I
>>>> admit strange things happen.

>>> take the rear wheel out and place it with the axle on a wooden
>>> block. then press with both hands in opposite placed gently
>>> downward. with the gear side down, the wheel will be impressively
>>> rigid. but gear side up, it will flex to the point where the
>>> non-drive side spokes go completely slack - with ease. thicker
>>> spokes [and stiffer rim] mitigate that to a good degree. of the
>>> two components, frame or wheel, the latter is by far the cheaper
>>> and simpler to address.

>> What evidence do you have that the rear wheel is the source of this
>> instability?

> because the stiffer wheel stopped it. resonance is a function of
> both mass and spring constant. remember?

That is a nice concept but it doesn't apply here. The shimmy is not
at the ground contact nor in the saddle, so it cant be in the rear of
the bicycle. What moves is the head tube and it oscillates about the
mass of the rider anchoring the saddle. The front wheel also has
little effect on this as shown by the shimmy tests with wheels of
widely different number of spokes, from 36 to Rolf Vector Pro wheels.

Even a water filled front wheel does not arrest shimmy as has been
tested.

Jobst Brandt

[Tim McNamara]

In article >,
jim beam > wrote:

> so how exactly did this testing determine that the rider is the
> cause? i say this is merely typical jobstian speculative guesswork.
> if it were true, all my bikes would shimmy. they don't.

According to your own posts, bike frames are springs that return 100% of
the energy input with no damping. If that's the case, all bikes shimmy
under the right conditions.

> and if a bike has a shimmy frequency the same as /any/ form of
> induction, and that shimmy can reach sufficient amplitude to throw a
> rider, it's a problem that needs to be properly dealt with. this
> ridiculous attitude of "it's the riders fault so let's not bother
> dealing with it" is just stupid beyond belief. especially when it's
> so easily fixed.
> >
> > http://www.sheldonbrown.com/brandt/shimmy.html
>
> propagation of your baseless unscientific drivellings are a massive
> negative for the credibility of the bike industry.

LOL! Yes, because Sheldon is *such* a patsy!

[[email protected]]

Bob Prohaska writes:

>> That is similar to the experience I had years ago and now and then
>> since. That's what made the hands-on shimmy problem apparent to
>> me.

> If you'll forgive me for trying to steal back the thread, what's the
> story with hands _off_ shimmy? Basically I'm asking if this is apt
> to be a correctable problem (as suggested by the rear wheel
> stiffness argument) or an inherently inalterable property of the
> frame.

It depends on the frame but it can be altered by mass of the handlebar
and length of bar stem forward extension.

Try attaching a weight to the front of the bars ans see what change
you get. My bicycle shimmies whenever I get in that speed range but
then I generally am coasting downhill at that speed and lay my knee
against the top tube. I realize that isn't so easy today with tiny
frame and sloping top tubes.

When I coast down mountains at high speeds, I have my hands on the
stem and am tucked in with both knees together at the top tube with
elbows tight there too. I have never allowed the bicycle to shimmy at
high speed but hen I'm not sure it would at over 40mph.

Jobst Brandt

[jim beam]

wrote:
> Johnnie Walker writes:
>
>
>>>>>>well, whether you want to live with it is your choice. the
>>>>>>ultimate cure is replacement with a big tubed frame as mentioned
>>>>>>before. but the stiffer wheel trick will definitely be an
>>>>>>improvement. just rebuild the rear with 2.0mm plain gauge
>>>>>>spokes on the drive side and re-use everything else.
>
>
>>>>>Would you attribute the improvement to the stiffer construction
>>>>>of the big tubed frame, or the difference in steering head angle?
>
>
>>>>angle [trail], etc. affects the amount of "correction" [input]
>>>>force the system experiences, but it doesn't affect frequency.
>>>>that's the result of the spring constants of the components and
>>>>their masses. some bikes may be more prone to shimmy as a result
>>>>of differences in trail, but imo, if a bike can easily be
>>>>deliberately /induced/ to shimmy, it's going to happen when you
>>>>don't want it to as well. i had a crash a few years back as a
>>>>result of sudden shimmy onset, and i had neither the time nor
>>>>balance to do anything about it. i cracked my hip and was in pain
>>>>for about a year. sure, shimmy can be "controlled", but i don't
>>>>think the rider should have to. especially as the cure is so
>>>>simple and costs no more at the frame manufacturing stage.
>
>
>>>From this I take it your hands were on the bars. If that is
>>>correct, then you were the cause of the shimmy.
>
>
>>no, hands off.
>
>
> The why didn't you put your hands on the bars and stop it. It takes a
> bit of time to build up to a hazardous level. Besides, as you reached
> for the bars you could have damped the whole thing out with the leg
> against the top tube.

two things jobst.
1. "sudden onset".
2. since this was, by your definition, /not/ rider induced, why did it
start? according to you, if the rider's the sole cause, riding hands
free is the solution, not the cure.

>
>
>>> I think this has been hashed over enough on this forum and tested
>>>by riders including Damon Rinard who performed instrumented shimmy
>>>tests of different wheels for TREK.
>
>
>>so how exactly did this testing determine that the rider is the
>>cause? i say this is merely typical jobstian speculative guesswork.
>>if it were true, all my bikes would shimmy. they don't.
>
>
> If you didn't have your hands on the bars you logically would have
> taken the effort to put them there rather than watch the effect
> snowball into a crash. Therefore, it is reasonable to assume you had
> your hands on the bars.

ok, so how exactly did this testing determine that the rider is the cause?

>
>
>>and if a bike has a shimmy frequency the same as /any/ form of
>>induction, and that shimmy can reach sufficient amplitude to throw a
>>rider, it's a problem that needs to be properly dealt with. this
>>ridiculous attitude of "it's the riders fault so let's not bother
>>dealing with it" is just stupid beyond belief. especially when it's
>>so easily fixed.
>
>
> Well, it might throw a novice rider who has never experienced this. I
> assumed you had enough experience, from all the things you write about
> here to not be one of those.
>
> http://www.sheldonbrown.com/brandt/shimmy.html

ah, the good old jobstian ad hominem. why don't you address the central
point of this asinine debate? what do /you/ propose to cure this highly
dangerous phenomenon jobst? /i/ say increasing torsional frame
stiffness is the cure, and a stiffer rear wheel helps. do you deny that?

>
>
>>propagation of your baseless unscientific drivellings are a massive
>>negative for the credibility of the bike industry.
>
>
> You'll have to show more than hyperbole to discount what I wrote on
> the subject.

jobst, i've experimented with stiffer frames and stiffer wheels. as
previously described. they address the issues. you just bleat
speculatively on biomechanical tangents. you do nothing to cure. no
cure, no science = wasted electrons.

>
>
>>>>>I've toyed with the idea of going to modern rim sizes; 27 inch is
>>>>>fairly ancient nowadays. Perhaps I should consider a new (extra)
>>>>>wheelset. It would certainly offer a clean comparison. It's
>>>>>hard for me to believe that the rear wheel is the culprit, but I
>>>>>admit strange things happen.
>
>
>>>>take the rear wheel out and place it with the axle on a wooden
>>>>block. then press with both hands in opposite placed gently
>>>>downward. with the gear side down, the wheel will be impressively
>>>>rigid. but gear side up, it will flex to the point where the
>>>>non-drive side spokes go completely slack - with ease. thicker
>>>>spokes [and stiffer rim] mitigate that to a good degree. of the
>>>>two components, frame or wheel, the latter is by far the cheaper
>>>>and simpler to address.
>
>
>>>What evidence do you have that the rear wheel is the source of this
>>>instability?
>
>
>>because the stiffer wheel stopped it. resonance is a function of
>>both mass and spring constant. remember?
>
>
> That is a nice concept but it doesn't apply here. The shimmy is not
> at the ground contact nor in the saddle, so it cant be in the rear of
> the bicycle.

ah, the jobstian "deny the facts if they get too uncomfortable" trick.
sorry jobst. no dice. it works. fact.

> What moves is the head tube and it oscillates about the
> mass of the rider anchoring the saddle.

yes, but throwing in a grain of truth doesn't sweeten a whole barrelfull
of putrefaction.

> The front wheel also has
> little effect on this as shown by the shimmy tests with wheels of
> widely different number of spokes, from 36 to Rolf Vector Pro wheels.

and that's why i've been discussing rears and frames!!!

>
> Even a water filled front wheel does not arrest shimmy as has been
> tested.

see above. and address the core issues jobst. mass and spring
constant. the rear springs because it's dished. the frame experiences
torsion. what have /you/ done to research these two factors? hint:
blaming the rider doesn't count.

>
> Jobst Brandt

[jim beam]

Tim McNamara wrote:
> In article >,
> jim beam > wrote:
>
>
>>so how exactly did this testing determine that the rider is the
>>cause? i say this is merely typical jobstian speculative guesswork.
>>if it were true, all my bikes would shimmy. they don't.
>
>
> According to your own posts, bike frames are springs that return 100% of
> the energy input with no damping. If that's the case, all bikes shimmy
> under the right conditions.

not if the harmonics don't coincide.

>
>
>>and if a bike has a shimmy frequency the same as /any/ form of
>>induction, and that shimmy can reach sufficient amplitude to throw a
>>rider, it's a problem that needs to be properly dealt with. this
>>ridiculous attitude of "it's the riders fault so let's not bother
>>dealing with it" is just stupid beyond belief. especially when it's
>>so easily fixed.
>>
>>>http://www.sheldonbrown.com/brandt/shimmy.html
>>
>>propagation of your baseless unscientific drivellings are a massive
>>negative for the credibility of the bike industry.
>
>
> LOL! Yes, because Sheldon is *such* a patsy!

[Joe Riel]

jim beam > writes:

> the rear springs because it's dished.

What does the dish have to do with it? As I pointed out several
weeks ago, in another thread, dishing the wheel makes its stiffer
compared to an undished wheel with the same spokes.

--
Joe Riel

[jim beam]

Joe Riel wrote:
> jim beam > writes:
>
>
>>the rear springs because it's dished.
>
>
> What does the dish have to do with it? As I pointed out several
> weeks ago, in another thread, dishing the wheel makes its stiffer
> compared to an undished wheel with the same spokes.
>
joe, you'll have to re-post. i missed it.

besides, dished wheels /do/ exhibit substantial flexibility on the drive
side due to reduced bracing angle. it's easily tested as described before.

[Tim McNamara]

In article >,
jim beam > wrote:

> Tim McNamara wrote:
> > In article >,
> > jim beam > wrote:
> >
> >
> >>so how exactly did this testing determine that the rider is the
> >>cause? i say this is merely typical jobstian speculative guesswork.
> >> if it were true, all my bikes would shimmy. they don't.
> >
> >
> > According to your own posts, bike frames are springs that return
> > 100% of the energy input with no damping. If that's the case, all
> > bikes shimmy under the right conditions.
>
> not if the harmonics don't coincide.

Ah, throw out the vague statement that sounds authoritative. Nice try,
but that dog don't hunt.

[jim beam]

Tim McNamara wrote:
> In article >,
> jim beam > wrote:
>
>
>>Tim McNamara wrote:
>>
>>>In article >,
>>> jim beam > wrote:
>>>
>>>
>>>
>>>>so how exactly did this testing determine that the rider is the
>>>>cause? i say this is merely typical jobstian speculative guesswork.
>>>>if it were true, all my bikes would shimmy. they don't.
>>>
>>>
>>>According to your own posts, bike frames are springs that return
>>>100% of the energy input with no damping. If that's the case, all
>>>bikes shimmy under the right conditions.
>>
>>not if the harmonics don't coincide.
>
>
> Ah, throw out the vague statement that sounds authoritative. Nice try,
> but that dog don't hunt.

what's confusing or difficult tim? look up "interference" with regard
to oscillation. every time you run up against /your/ knowledge barrier,
it's /my/ fault and /i'm/ the bull****ter. wtf's up with that? can't
you own your own problems?

[Tim McNamara]

In article >,
jim beam > wrote:

> Tim McNamara wrote:
> > In article >,
> > jim beam > wrote:
> >
> >>Tim McNamara wrote:
> >>
> >>>In article >,
> >>> jim beam > wrote:
> >>>
> >>>>so how exactly did this testing determine that the rider is the
> >>>>cause? i say this is merely typical jobstian speculative guesswork.
> >>>>if it were true, all my bikes would shimmy. they don't.
> >>>
> >>>According to your own posts, bike frames are springs that return
> >>>100% of the energy input with no damping. If that's the case, all
> >>>bikes shimmy under the right conditions.
> >>
> >>not if the harmonics don't coincide.
> >
> > Ah, throw out the vague statement that sounds authoritative. Nice try,
> > but that dog don't hunt.
>
> what's confusing or difficult tim? look up "interference" with regard
> to oscillation. every time you run up against /your/ knowledge barrier,
> it's /my/ fault and /i'm/ the bull****ter. wtf's up with that? can't
> you own your own problems?

Oh jim, there you go again. I didn't say "confusing or difficult." I
said "vague." Once again you're off on the red herring hunt.

[Tim McNamara]

In article >,
jim beam > wrote:

> Joe Riel wrote:
> > jim beam > writes:
> >
> >>the rear springs because it's dished.
> >
> > What does the dish have to do with it? As I pointed out several
> > weeks ago, in another thread, dishing the wheel makes its stiffer
> > compared to an undished wheel with the same spokes.
>
> joe, you'll have to re-post. i missed it.

Ditto.

> besides, dished wheels /do/ exhibit substantial flexibility on the
> drive side due to reduced bracing angle. it's easily tested as
> described before.

In informal measurements, e.g. putting the wheel in my truing stand and
pushing the rim sideways, I also find that dished wheels are more
laterally flexible.

[jim beam]

Tim McNamara wrote:
> In article >,
> jim beam > wrote:
>
>
>>Tim McNamara wrote:
>>
>>>In article >,
>>> jim beam > wrote:
>>>
>>>
>>>>Tim McNamara wrote:
>>>>
>>>>
>>>>>In article >,
>>>>>jim beam > wrote:
>>>>>
>>>>>
>>>>>>so how exactly did this testing determine that the rider is the
>>>>>>cause? i say this is merely typical jobstian speculative guesswork.
>>>>>>if it were true, all my bikes would shimmy. they don't.
>>>>>
>>>>>According to your own posts, bike frames are springs that return
>>>>>100% of the energy input with no damping. If that's the case, all
>>>>>bikes shimmy under the right conditions.
>>>>
>>>>not if the harmonics don't coincide.
>>>
>>>Ah, throw out the vague statement that sounds authoritative. Nice try,
>>>but that dog don't hunt.
>>
>>what's confusing or difficult tim? look up "interference" with regard
>>to oscillation. every time you run up against /your/ knowledge barrier,
>>it's /my/ fault and /i'm/ the bull****ter. wtf's up with that? can't
>>you own your own problems?
>
>
> Oh jim, there you go again. I didn't say "confusing or difficult." I
> said "vague." Once again you're off on the red herring hunt.

no, /i/ observed that /you/ were finding the physics confusing and
difficult. no herrings. if you read up on this stuff, then come back
with questions, i'll help. but wrongly faulting me for your own lack of
knowledge then childishly flinging excrement in your frustration is
simply stupid.

[Peter Cole]

wrote:
> Bob Prohaska writes:
>
>>> That is similar to the experience I had years ago and now and then
>>> since. That's what made the hands-on shimmy problem apparent to
>>> me.
>
>> If you'll forgive me for trying to steal back the thread, what's the
>> story with hands _off_ shimmy? Basically I'm asking if this is apt
>> to be a correctable problem (as suggested by the rear wheel
>> stiffness argument) or an inherently inalterable property of the
>> frame.
>
> It depends on the frame but it can be altered by mass of the handlebar
> and length of bar stem forward extension.
>
> Try attaching a weight to the front of the bars ans see what change
> you get. My bicycle shimmies whenever I get in that speed range but
> then I generally am coasting downhill at that speed and lay my knee
> against the top tube. I realize that isn't so easy today with tiny
> frame and sloping top tubes.

I ride no-hands a lot, even at high speeds (30-40mph). I'm very tall and
my bike frames are typically 68cm or so. Despite all that, I never have
encountered shimmy on any of the 5 or 6 road bikes I've had except on
one occasion. That was when I attached a rather heavy light to my
aerobars. I had approximately a pound or two perhaps 12-18" in front of
the steering axis. The bike developed relatively mild no-hands shimmy.

[Joe Riel]

Tim McNamara > writes:

> In article >,
> jim beam > wrote:
>
>> Joe Riel wrote:
>> > jim beam > writes:
>> >
>> >>the rear springs because it's dished.
>> >
>> > What does the dish have to do with it? As I pointed out several
>> > weeks ago, in another thread, dishing the wheel makes its stiffer
>> > compared to an undished wheel with the same spokes.
>>
>> joe, you'll have to re-post. i missed it.
>
> Ditto.
>
>> besides, dished wheels /do/ exhibit substantial flexibility on the
>> drive side due to reduced bracing angle. it's easily tested as
>> described before.
>
> In informal measurements, e.g. putting the wheel in my truing stand and
> pushing the rim sideways, I also find that dished wheels are more
> laterally flexible.

It was the "Spoke tension question" thread, early January 2006.
Quoting myself,

Something I hadn't realized is that the offset in the rear wheel
stiffens it laterally (not much). That is, for a given flange
spacing, the *minimum* lateral stiffness occurs when there is no
offset. Maybe I'll start marketing offset front wheels 8-). Of
course, the increase in stiffness comes at a cost, the wheels are
not as *strong*.

A pertinent equation (with a few typos, but not serious) preceded
it by several posts.

Directly comparing rear and front wheels isn't fair, you have to
compare wheels with the same hub flange spacing. However, I won't
(yet 8-) take issue with the revised statement: the rear [springs]
because the flange spacing is smaller (which is caused by the offset).

--
Joe Riel

[Tim McNamara]

In article >,
jim beam > wrote:

> Tim McNamara wrote:
> > In article >,
> > jim beam > wrote:
> >
> >>Tim McNamara wrote:
> >>
> >>>In article >,
> >>> jim beam > wrote:
> >>>
> >>>>Tim McNamara wrote:
> >>>>
> >>>>>In article >, jim
> >>>>>beam > wrote:
> >>>>>
> >>>>>>so how exactly did this testing determine that the rider is the
> >>>>>>cause? i say this is merely typical jobstian speculative
> >>>>>>guesswork. if it were true, all my bikes would shimmy. they
> >>>>>>don't.
> >>>>>
> >>>>>According to your own posts, bike frames are springs that return
> >>>>>100% of the energy input with no damping. If that's the case,
> >>>>>all bikes shimmy under the right conditions.
> >>>>
> >>>>not if the harmonics don't coincide.
> >>>
> >>>Ah, throw out the vague statement that sounds authoritative. Nice
> >>>try, but that dog don't hunt.
> >>
> >>what's confusing or difficult tim? look up "interference" with
> >>regard to oscillation. every time you run up against /your/
> >>knowledge barrier, it's /my/ fault and /i'm/ the bull****ter.
> >>wtf's up with that? can't you own your own problems?
> >
> > Oh jim, there you go again. I didn't say "confusing or difficult."
> > I said "vague." Once again you're off on the red herring hunt.
>
> no, /i/ observed that /you/ were finding the physics confusing and
> difficult.

No, you didn't *observe* anything of the sort. If you think you did,
then you are hallucinating. Perhaps you should differentiate more
accurately between "observation" and "supposition."

> no herrings. if you read up on this stuff, then come back with
> questions, i'll help. but wrongly faulting me for your own lack of
> knowledge then childishly flinging excrement in your frustration is
> simply stupid.

LOL. It's not like this is rocket science, jim. You do like being
obfuscatory in your effort to convince people that you're right in your
witch hunt, but few people seem to fall for it and none with an
engineering background. Why is that, anyway?

[jim beam]

Tim McNamara wrote:
> In article >,
> jim beam > wrote:
>
>
>>Tim McNamara wrote:
>>
>>>In article >,
>>> jim beam > wrote:
>>>
>>>
>>>>Tim McNamara wrote:
>>>>
>>>>
>>>>>In article >,
>>>>>jim beam > wrote:
>>>>>
>>>>>
>>>>>>Tim McNamara wrote:
>>>>>>
>>>>>>
>>>>>>>In article >, jim
>>>>>>>beam > wrote:
>>>>>>>
>>>>>>>
>>>>>>>>so how exactly did this testing determine that the rider is the
>>>>>>>>cause? i say this is merely typical jobstian speculative
>>>>>>>>guesswork. if it were true, all my bikes would shimmy. they
>>>>>>>>don't.
>>>>>>>
>>>>>>>According to your own posts, bike frames are springs that return
>>>>>>>100% of the energy input with no damping. If that's the case,
>>>>>>>all bikes shimmy under the right conditions.
>>>>>>
>>>>>>not if the harmonics don't coincide.
>>>>>
>>>>>Ah, throw out the vague statement that sounds authoritative. Nice
>>>>>try, but that dog don't hunt.
>>>>
>>>>what's confusing or difficult tim? look up "interference" with
>>>>regard to oscillation. every time you run up against /your/
>>>>knowledge barrier, it's /my/ fault and /i'm/ the bull****ter.
>>>>wtf's up with that? can't you own your own problems?
>>>
>>>Oh jim, there you go again. I didn't say "confusing or difficult."
>>> I said "vague." Once again you're off on the red herring hunt.
>>
>>no, /i/ observed that /you/ were finding the physics confusing and
>>difficult.
>
>
> No, you didn't *observe* anything of the sort. If you think you did,
> then you are hallucinating. Perhaps you should differentiate more
> accurately between "observation" and "supposition."

ok, so having just done your homework on interference and harmonics,
please explain the effects of having two components resonating at the
same frequency and two that don't. thanks.

>
>
>>no herrings. if you read up on this stuff, then come back with
>>questions, i'll help. but wrongly faulting me for your own lack of
>>knowledge then childishly flinging excrement in your frustration is
>>simply stupid.
>
>
> LOL. It's not like this is rocket science, jim. You do like being
> obfuscatory in your effort to convince people that you're right in your
> witch hunt, but few people seem to fall for it and none with an
> engineering background. Why is that, anyway?

whatever tim. you don't know what you don't know.

[Mujambo]

Tim McNamara wrote:
> In article >,
> jim beam > wrote:

>
>> no herrings. if you read up on this stuff, then come back with
>> questions, i'll help. but wrongly faulting me for your own lack of
>> knowledge then childishly flinging excrement in your frustration is
>> simply stupid.
>
> LOL. It's not like this is rocket science, jim. You do like being
> obfuscatory in your effort to convince people that you're right in your
> witch hunt, but few people seem to fall for it and none with an
> engineering background. Why is that, anyway?

Urm, because jim only has a little knowledge, and that the saying about
those with only a little knowledge is true... he's pretty good at
insults and bull**** jargon when he's cornered, though. That's gotta
count for something, doesn't it?