"The Stability of the Bicycle"

"Phil Holman" writes:

"Simon Brooke" wrote in message
news
On Sat, 11 Oct 2003 19:26:34 +0000, Phil Holman wrote:

I tried it with a hill bike which happened to be indoors as my road
bike
(which I've done all the rest of my tests on) is in the shed. This has
a
relatively heavy tyre and short stem; nevertheless my results accord
with
yours: spinning the wheel either way does not make an appreciable
difference - mass imbalance overwhelms it. Once again, I would be
happy to
film this and post a quicktime.
Jobst?

Yes please do, a picture is worth a 1000 words.

And a movie costs as much as a million to download, so it better be
worth a million... Please be kind to my line.

URL: http://www.jasmine.org.uk/~simon/tmp/tilt_or_gyro.MOV

The bicycle is (as you can see) suspended in a front down attitude, as
recommended. What you can't see is that the head tube is vertical,
although in my trials this wasn't at all critical.

If anyone thinks this is not conclusive, would they care to repeat the
experiment and post their own movie?

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

See one nuclear war, you've seen them all.

writes:

Simon Brooke writes:

I'm thinking you have the front wheel resting on the ground. The
instruction was to have the bike resting on your shoulder with top
tube angled down just enough for the stationary front wheel to stay
straight ahead (not touching the ground). Spin the front wheel
forward and lean to the left and the steering will turn to the left
under both mass imbalance and gyroscopic effect. Now spin the wheel
backwards and lean to the left and the wheel will turn in the
direction of the dominant force. Left and it's mass imbalance,
right and it's gyroscopic effect. My result was left but I can see
where a much shorter stem, regular brake levers and a heavy front
wheel could result in it turning right.

I tried it with a hill bike which happened to be indoors as my road
^^

Please explain what "it" is in this context. As was mentioned in the
first paragraph above, you seem to have the front wheel on the ground
which is not "it" the experiment I outlined.

I tried exactly the experiment you described, with the front wheel
off the ground and the top tube angled down. I have now repeated it on
film, with a road bike. The movie is he
URL: http://www.jasmine.org.uk/~simon/tmp/tilt_or_gyro.MOV

If you achieve different results from this experiment, or still wish
to claim that my test method is flawed, would you care to post a
movie?

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

See one nuclear war, you've seen them all.

"Simon Brooke" wrote in message
. uk...
"Phil Holman" writes:

"Simon Brooke" wrote in message
news
On Sat, 11 Oct 2003 19:26:34 +0000, Phil Holman wrote:

I tried it with a hill bike which happened to be indoors as my
road
bike
(which I've done all the rest of my tests on) is in the shed. This
has
a
relatively heavy tyre and short stem; nevertheless my results
accord
with
yours: spinning the wheel either way does not make an appreciable
difference - mass imbalance overwhelms it. Once again, I would be
happy to
film this and post a quicktime.
Jobst?

Yes please do, a picture is worth a 1000 words.

And a movie costs as much as a million to download, so it better be
worth a million... Please be kind to my line.

URL: http://www.jasmine.org.uk/~simon/tmp/tilt_or_gyro.MOV

The bicycle is (as you can see) suspended in a front down attitude, as
recommended. What you can't see is that the head tube is vertical,
although in my trials this wasn't at all critical.

If anyone thinks this is not conclusive, would they care to repeat the
experiment and post their own movie?

Yep, that pretty much falls into line with what I found although the
required lean angle appears larger (indexed steering maybe). Thanks for
taking the time.

Phil Holman

[ snip ]

I tried exactly the experiment you described, with the front wheel
off the ground and the top tube angled down. I have now repeated it on
film, with a road bike. The movie is he

URL: http://www.jasmine.org.uk/~simon/tmp/tilt_or_gyro.MOV


Dear Simon,

Your movie is now available for download from:

http://home.comcast.net/~carlfogel/d...lt_or_gyro.mov

It's a cable connection and utterly unused (created today),
so no worries about tying up any line or system. The file
is about 7mb and took 63 minutes to download from your site,
but uploaded in about 3 minutes from my system to the new
web page.

It was such fun setting up the web page that I suppose
that I ought to get some popcorn and figure out how to
view the movie. But then I see myself more as a studio
mogul, raking in vast profits from distribution, not
what Hitchcock referred to as--well, let's not pursue
that line.

See you on Oscar night.

Carl Fogel

(Carl Fogel) writes:

[ snip ]

I tried exactly the experiment you described, with the front wheel
off the ground and the top tube angled down. I have now repeated it on
film, with a road bike. The movie is he

URL: http://www.jasmine.org.uk/~simon/tmp/tilt_or_gyro.MOV

Your movie is now available for download from:

http://home.comcast.net/~carlfogel/d...lt_or_gyro.mov

Many thanks for that.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

Due to financial constraints, the light at the end of the tunnel
has been switched off.

writes:


Place the bicycle on the 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.

Could the mass of the stem, bars and brake levers/brifters overwhelm
the gyroscopic forces? Would this experiment be clearer with the stem
removed off the steerer, so that the effects of the mass of the stem
and its dependents are removed? The reason I ask is that it's best
to remove the stem and wheel when adjusting the headset, as the mass
of those items makes it hard to distinguish the proper bearing preload.

A Muzi wrote in message ...
Are you part of the Gene Daniels school of Usenet posting?

Carl Fogel wrote:
Dear Andrew,


-snip a misattributed selection which is either hilarious or
slander depending on whether your name is Gene Daniels or not-

-blah blah blah-

Incidentally, I found to my horror that the otherwise
reliable Sheldon Brown failed to scale his gear-inch
calculator down to the clown-cycle 4-inch wheel level that
you mentioned elsewhere in the Dahon thread (see how easily
even decent people are caught up in depravity?), so I'm about
to plead publicly with him to reveal all that he knows about
honest-to-God circus-clown bicycles.


Hey! Watch your attributions! That's _not_ my quotation! I
thoroughly enjoy my correspondence with Gene off this forum
and I have no reason to say such a thing.

(That was from Ted Bennett on 17 July of this year, BTW, and
kind of humorous.)

If you wish to express gear inches, it's (chainring
teeth/driven cog teeth)*nominal wheel diameter.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"Tim McNamara" wrote in message
...
writes:


Place the bicycle on the 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.

Could the mass of the stem, bars and brake levers/brifters overwhelm
the gyroscopic forces?

Exactly.

Would this experiment be clearer with the stem
removed off the steerer, so that the effects of the mass of the stem
and its dependents are removed?

That would isolate the gyroscopic effect somewhat. There is still some
mass imbalance because the steering axis does not bisect the wheel in
two equal halves.


The reason I ask is that it's best
to remove the stem and wheel when adjusting the headset, as the mass
of those items makes it hard to distinguish the proper bearing
preload.

This really defeats the object of the exercise (to determine the
steering force from leaning when wheeling a bicycle along while holding
the seat).

Phil Holman

A Muzi wrote in message ...
A Muzi wrote in message ...
Are you part of the Gene Daniels school of Usenet posting?

Carl Fogel wrote:
Dear Andrew,

-snip a misattributed selection which is either hilarious or
slander depending on whether your name is Gene Daniels or not-

Hey! Watch your attributions! That's _not_ my quotation! I
thoroughly enjoy my correspondence with Gene off this forum
and I have no reason to say such a thing.

(That was from Ted Bennett on 17 July of this year, BTW, and
kind of humorous.)


Dear Andrew,

You're absolutely right--I looked again and the quote was,
as you say, from Ted Bennett, not you (I'll lie low and
spare him my grovelling unless he posts and notices the
outrage).

I was trying to find posts about "gene daniels" to figure
out what you meant, found only two, and promptly confused
Ted's post with yours.

Sorry--it was the Coca-Cola talking.

Carl Fogel

A Muzi wrote in message ...
A Muzi wrote in message ...
Are you part of the Gene Daniels school of Usenet posting?

Carl Fogel wrote:
Dear Andrew,


-snip a misattributed selection which is either hilarious or
slander depending on whether your name is Gene Daniels or not-

Hey! Watch your attributions! That's _not_ my quotation! I
thoroughly enjoy my correspondence with Gene off this forum
and I have no reason to say such a thing.

(That was from Ted Bennett on 17 July of this year, BTW, and
kind of humorous.)

[snip]

Dear Andrew,

You're absolutely right--I looked again and the quote was
as you say, from Ted Bennett, not you (I'll lie low and
spare him my grovelling unless he posts and notices the
outrage).

I was trying to find posts about "gene daniels," found only
two, and promptly confused Ted's post with yours.

Sorry--it was the Coca-Cola talking.

Carl Fogel