"The Stability of the Bicycle"

Benjamin Lewis wrote:

Sorry, it was a different bicycle on which the forks were reversed. This
bicycle had normal forks, and yet was nearly impossible to ride no hands
due to the lack of gyroscopic effects.

But 1) this bicycle was already difficult to ride no-handed when the
gyroscopic effects were not being canceled, and 2) it was still possible to
ride it no-handed without the gyroscopic effects, although that made it
still more difficult. This contradicts the claim that lack of gyroscopic
effects would make no-handed riding impossible.

http://tinyurl.com/pswa

wrote:

Benjamin Lewis wrote:

Sorry, it was a different bicycle on which the forks were reversed.
This bicycle had normal forks, and yet was nearly impossible to ride no
hands due to the lack of gyroscopic effects.

But 1) this bicycle was already difficult to ride no-handed when the
gyroscopic effects were not being canceled, and 2) it was still possible
to ride it no-handed without the gyroscopic effects, although that made
it still more difficult. This contradicts the claim that lack of
gyroscopic effects would make no-handed riding impossible.

http://tinyurl.com/pswa

Perhaps I missed something in this article, but if I read it correctly:

There was only one bicycle that had gyroscopic forces cancelled (the "URB
I"), and it had normal forks. This bicycle was easy to ride with hands on
the bars, but "almost impossible" to ride no-hands.

None of the other bicycles had counter-rotating wheels, and thus had normal
gyroscopic forces.

I suspect the reason the "URB I" was merely "almost impossible" and not
completely impossible to ride no-hands is due to the same reason crude
steering can be done by tilting a stationary bike (fork/wheel geometry).

--
Benjamin Lewis

A small, but vocal, contingent even argues that tin is superior, but they
are held by most to be the lunatic fringe of Foil Deflector Beanie science.

"Phil Holman" wrote in message
m...
"W K" wrote in message
...
wrote in message
...

When walking a bicycle, holding it by the saddle, lean angles are
trivially small and cause steering by gyroscopic action

I don't see how you get that conclusion from the below.

the test for
which you have apparently not done. Take the wheel out of the
bicycle, turn it at "walking speed" and tilt it to the left and right
in your hands. You will notice a quick and relatively forceful
steering response.

Yep.

It is this force that allows the bicycle to be
steered by slight lean angles

Very slight indeed.

I have an alternative experiment I'd like you to comment on:
Take whole bike, put back wheel on a brick so it can be held
horizontally.

Tip bike slightly to one side, and see the way the steering goes.

I did this for:
a) wheels stationary - steering flops to one side.
b) wheel going at 20 kph - could not see any difference.
c) wheel going at 20kph BACKWARDS - very slight effect of steering going
opposite direction. With several attempts I only saw this happen once,
and
it was soon overcome by a similar "flop" to (a).

No Maths for the above, but it shows the gyroscope effect is easily
swamped
by other effects.

I'm not picturing what you did exactly but you bring up an interesting
point.

More or less: spin the wheel and tip the bike to one side.
All other points, about keeping the bike horizontal (hub-hub), or to try to
stop "steering flop" are side issues.

The front wheel turning backwards. If a bicycle is wheeled
backwards, and I assume according to Jobst's hypothesis, the
gyroscopic effect should steer the front wheel in the opposite
direction. I haven't done the test yet but for some, it may bring
clarity to the situation as to which is the dominant force......or
not.

(no clarity actually, but thats perhaps the point. certainly not an obvious
"opposite" effect)

Two other points.

I have a utility/mountain bike (probably a frame designed for a
longer,suspension fork), due to its steering properties its difficult to
ride no hands. Do you think it would be easier to ride it like this with
heavier front wheels? After all, it has got relatively heavy wheels!

Tandems.
These are designed so that "body steering" is more difficult. Not so that
you cannot ride them with no hands, but so that unexpected stoker movements
do not upset the steering of the thing.
Is this down to lighter front wheels with less gyroscopic force, or down to
the geometry of the steering angles?

Tandem FAQs give the above as a reason NOT to buy an old one, or an old
frame without the correct frame and fork configurations.

Benjamin Lewis wrote:

wrote:


Benjamin Lewis wrote:


Sorry, it was a different bicycle on which the forks were reversed.
This bicycle had normal forks, and yet was nearly impossible to ride no
hands due to the lack of gyroscopic effects.

But 1) this bicycle was already difficult to ride no-handed when the
gyroscopic effects were not being canceled, and 2) it was still possible
to ride it no-handed without the gyroscopic effects, although that made
it still more difficult. This contradicts the claim that lack of
gyroscopic effects would make no-handed riding impossible.


http://tinyurl.com/pswa

Perhaps I missed something in this article, but if I read it correctly:

There was only one bicycle that had gyroscopic forces cancelled (the "URB
I"), and it had normal forks. This bicycle was easy to ride with hands on
the bars, but "almost impossible" to ride no-hands.

Unfortunately I am not able to get the above URL to work at the moment, but
my recollection of the original Physics Today article was that URB-I was
awkward and difficult to ride no-handed even with the second front wheel
stationary (i.e. retaining the normal gyroscopic effects). This may be due
to the extra weight (esp. off-center) of the extra wheel. Spinning this
wheel backwards made it substantially harder to ride no-handed, but it was
still possible.

None of the other bicycles had counter-rotating wheels, and thus had normal
gyroscopic forces.

That is my recollection as well.

I suspect the reason the "URB I" was merely "almost impossible" and not
completely impossible to ride no-hands is due to the same reason crude
steering can be done by tilting a stationary bike (fork/wheel geometry).

I agree, but the issue was whether the lean steering done when walking a
bicycle by just holding the seat is the result of 1) only gyroscopic
effects, 2) only the steering geometry effects, or 3) a significant
combination of both. Jobst's claim was that this lean steering was
specifically not the result of the steering geometry that makes the front
wheel flop to the side when the bike is stationary and that only gyroscopic
effects cause the steering in this situation.

WK's tests with slight leans applied to a bike with the front wheel
spinning first forwards and then backwards argue that the effect from the
steering geometry is dominant. I have confirmed this result and also felt
it to be most likely given the very small gyroscopic forces I felt when
tilting a wheel that was rotating at walking speed.

The results of Jones' tests with URB-I argue for a combination of
gyroscopic forces and steering geometry playing a significant role since
elimination of gyroscopic effects made it more difficult but not impossible
to ride no-handed. It would be interesting to see how hard a bike with only
the gyroscopic effects but lacking the normal steering geometry would be to
ride no-handed. E.g. use a 90 degree head tube angle and straight fork.

Simon Brooke wrote in message .uk...
(Carl Fogel) writes:

P.P.S. Double-dare ya' all to top this for linguistic
pedantry!

ITYMHM '_I_ _challenge_ _you_ to _better_ this for linguistic pedantry'.

The phrase 'you all' is a deprected colonial form; the 'all is
redundent and may be elided. 'Double-dare' is slang, and, worse,
vulgar.

Yours very sincerely,

Simon Brooke esquire, metapedant.

Dear Simon,

Say, Si--gotta ask ya' sump'n! What's that-there
ITYMHM? Ain't nuthin' on Google, 'leastways nuthin'
that this chile kin find. Oncet y'clear 'tall up,
I'll be right pleezed to look 'round fer them missin'
a's in yer pore li'l redundant deprecations--fair
trade, sure, t'aint no robbery, nohow! 'Course oncet
dust-settle, less you'n'me warsh our hands of this-here
foo-for-aw, 'fore all them others get sick-to-death
of us'n.

(Those who have never heard "oncet" spoken properly
may be tempted to pronounce this vanishing regionalism
as "once-it," the eye being fooled into voicing the
silent "e"--than which nothing could be more absurd,
as Bierce remarked of nations that use "j" as a vowel.
See his entry for "J" in the Devil's Dictionary
for the likely fate of linguistic quibblers.)

("Wunst" suggests the proper pronunciation of the oddly
excrescent "t", but this clearer orthography lacks the
dignity of tradition, just as "Chumley" has yet to replace
"Cholomondley.")

Carl Fogel, Junior Pettifogger

A problem with the Jones' article are the plots. He presents the data as
a fraction of the wheel radius. Most scientists want to show conclusions
in a non dimensional manner.

His presentation implies that trail should be a function of front wheel
radius. So designers have been talking about "Castor angel" ever since.
They should have been considering the total magnitude of trail.

After that, small wheeled bikes were built to a castor angle and had too
little trail. The bikes were too twitchy and the physicists said that it
was because the small wheels didn't have enough gyroscopic moment. When
in fact, the bikes were built to some castor angle myth and needed more
trail.

A bike handles properly when in has a "control spring" This is a
centering spring that gives us feedback when we steer. As a bike goes
faster, the handlebars get harder to move. Therefore the bike isn't
twitchy. Trail is one method of doing this. There are several others.
One is to add lead weights to the wheel rims.

We have built 350 of so weird bikes to study these effects. We still
don't know all the answers. I can tell you that the answers are not in
Jones' article. Or publications that echo his conclusions.


--
Bill "Pop Pop" Patterson
Retired and riding
my front drive low racer
and our M5 tandem.

See some Bikes At:

http://home.earthlink.net/~wm.patterson/index.html

PC

http://www.roadkillbill.com/r135.html

Class and Helicopter

http://www.calpoly.edu/~wpatters/

Reply to

Simon Brooke writes:

You misunderstand me. The bicycle with a "counter gyroscopic
wheelset" has been tried by someone other than Jobst (I don't
remember the reference, but someone posted a link to an academic
paper the other day), and found by this person to be almost
impossible to ride no hands, as Jobst has claimed.

but it was quoted that the forks were reversed to remove the caster
action. that alone would make it very scary to no-hands ride. in
that context the gyro effects are meaningless

Just so. And yet is was 'very difficult but not impossible' to ride
no hands.

As someone already pointed out, reversing the fork increased caster by
a huge amount and that is why that configuration could be ridden. As
I said. the project was apparently undertaken by a non-bicycle rider
and his assessment of the results are so awkwardly worded that one can
only guess what he found.

Just the fact that he said reversing the fork got rid of the caster
effect makes the whole project an unproductive mess. His description
of it is unintelligible in practical terms. He did not define his
terms and did not use them consistently. The whole idea is ridiculous
because one who has seen stunt riders perform knows that ant bicycle
is ridable if it has at least one working wheel.

Citing this report does not add any substance or clarity to anyone's
premises.

Jobst Brandt

Phil Holman writes:

I'm not picturing what you did exactly but you bring up an
interesting point. The front wheel turning backwards. If a bicycle
is wheeled backwards, and I assume according to Jobst's hypothesis,
the gyroscopic effect should steer the front wheel in the opposite
direction. I haven't done the test yet but for some, it may bring
clarity to the situation as to which is the dominant force... or
not.

Good point. So place your bicycle on your shoulder such that it rests
there in the crotch of top and seat tube, top tube sloping forward
just enough to make the wheel stay straight ahead with the frame in a
vertical plane. Lean the bicycle to either side with the wheel not
turning and note that it responds as one would like steering to do,
turning to the side to which it is leaned.

Spin the wheel forward and there is no change although the response is
sharper. Spin the wheel rearward and the gyroscopic moment overwhelms
the caster or trail effect completely as the wheel steers the "wrong"
way. I think that is a conclusive test. Thanks Phil.

Once more, how does one pronounce "maths" (aloud)?

Jobst Brandt

wrote in message
...
Phil Holman writes:

I'm not picturing what you did exactly but you bring up an
interesting point. The front wheel turning backwards. If a bicycle
is wheeled backwards, and I assume according to Jobst's hypothesis,
the gyroscopic effect should steer the front wheel in the opposite
direction. I haven't done the test yet but for some, it may bring
clarity to the situation as to which is the dominant force... or
not.

Good point. So place your bicycle on your shoulder such that it rests
there in the crotch of top and seat tube, top tube sloping forward
just enough to make the wheel stay straight ahead with the frame in a
vertical plane. Lean the bicycle to either side with the wheel not
turning and note that it responds as one would like steering to do,
turning to the side to which it is leaned.

Spin the wheel forward and there is no change although the response is
sharper. Spin the wheel rearward and the gyroscopic moment overwhelms
the caster or trail effect completely as the wheel steers the "wrong"
way. I think that is a conclusive test. Thanks Phil.

Once more, how does one pronounce "maths" (aloud)?

Something like....Oh gawd blimey, I've left me maffs book at ome.

How do you think the experiment works with a 140mm stem, heavy STI
levers and a front wheel that weights 800 grms? Could it be that the
modern bike doesn't fit the old theories anymore.

Phil Holman

Phil Holman writes:

I'm not picturing what you did exactly but you bring up an
interesting point. The front wheel turning backwards. If a
bicycle is wheeled backwards, and I assume according to Jobst's
hypothesis, the gyroscopic effect should steer the front wheel in
the opposite direction. I haven't done the test yet but for some,
it may bring clarity to the situation as to which is the dominant
force... or not.

Good point. So place your bicycle on your shoulder such that it
rests there in the crotch of top and seat tube, top tube sloping
forward just enough to make the wheel stay straight ahead with the
frame in a vertical plane. Lean the bicycle to either side with
the wheel not turning and note that it responds as one would like
steering to do, turning to the side to which it is leaned.

Spin the wheel forward and there is no change although the response
is sharper. Spin the wheel rearward and the gyroscopic moment
overwhelms the caster or trail effect completely as the wheel
steers the "wrong" way. I think that is a conclusive test. Thanks
Phil.

Once more, how does one pronounce "maths" (aloud)?

Something like....Oh gawd blimey, I've left me maffs book at ome.

How do you think the experiment works with a 140mm stem, heavy STI
levers and a front wheel that weights 800 grams? Could it be that
the modern bike doesn't fit the old theories anymore.

I think that's what people, who have spent thousands of dollars on
bicycles with equipment under claims that do not to follow natural
'laws', like to believe. I think that's why they are willing to pay
thousands of dollars for specious advertising claims and believe they
can use similar arguments here on wreck.bike. Physics has not changed
in these respects. I think I hear my steel frame getting soft! It's
shimmying all by itself.

Jobst Brandt