Re: Gyroscopes - Usenet Physics FAQ - Reference frames

From: Tom Roberts (tjroberts_at_lucent.com)
Date: 08/04/04 

Date: Wed, 04 Aug 2004 00:18:35 GMT

greywolf42 wrote:
> "Myxococcus xanthus" <mold-guardian@comcast.net> wrote in message
> news:ce5e7813.0408030119.77bb3b25@posting.google.com...
>>Please do a google search for references to
>>Jones, David E.H., "The Stability of the Bicycle", Physics Today (April
>> 1970): 34-40
>>The gyroscopic contribution to bicycle stability is relatively minor.
>
> As a teenager -- purely as a scientific experiment ;) -- I repeatedly
> released an old bicycle to roll down a local hill. Except for the times it
> didn't make the turn, it stayed rolling for several hundred yards. That's
> hardly minor.

But, of course, the fact that an unoccupied bicycle can roll on its own
has nothing to do with gyroscopic action of its wheels. It can do that
because the geometry of its front fork provides feedback to make it
steer the wheels under its center of gravity. The couple formed by the
lean of the bike, the camber of the front wheel[#], and the weight of
the bike is MUCH larger than the gyroscopic force. And unlike the
latter, it is independent of speed, and works at low speeds (but not at
zero speed, so it does fall when friction brings it to a halt)

        [#] extend the axis of the front fork to the ground, and note
            it is in front of the wheel's point on the ground. That
            distance is called the camber. The front fork is usually
            bent forward to reduce the camber to the desired value for
            the inclination of the fork. Compare a racing bike and a
            touring bike....

If the effect were gyroscopic action then the bicycle would presumably
be stable going backwards also. Try it -- it isn't stable at all and
falls immediately -- the geometry of the front fork (at the rear) causes
oversteer.

Tom Roberts tjroberts@lucent.com

Relevant Pages

  • Re: Gyroscopes - Usenet Physics FAQ - Reference frames
    ... >>The gyroscopic contribution to bicycle stability is relatively minor. ... But, of course, the fact that an unoccupied bicycle can roll on its own ... latter, it is independent of speed, and works at low speeds (but not at ...
    (sci.physics)
  • Re: Gyroscopes - Usenet Physics FAQ - Reference frames
    ... >>The gyroscopic contribution to bicycle stability is relatively minor. ... But, of course, the fact that an unoccupied bicycle can roll on its own ... latter, it is independent of speed, and works at low speeds (but not at ...
    (sci.math)
  • Re: Tomorrows bike: anti-lock roller brakes -- and???
    ... The wheel continues to roll on the road as before while the bicycle ... the centre of mass of the whole thing including the rider is below ...
    (rec.bicycles.tech)
  • Re: Official ASC Roll Call for 2006 - Please Sign In
    ... >Please sign in below for the Official '2006' Roll Call. ... James Ervin ... "When I see an adult on a bicycle, I do not despair for the future of ...
    (alt.smokers.cigars)
  • Re: On low gears
    ... You and your bicycle should roll thirty feet or so. ... With gearing, the same gentle pushing lets practically any bicyclists ... The rider can't trade as much force for distance. ... Minor drags like these be easily ignored at higher speeds, ...
    (rec.bicycles.tech)