From: jthorn@galileo.thp.univie.ac.at (Jonathan Thornburg) Subject: bicycle stability (was: Re: Motorbike wheels.) Date: 10 May 2000 10:51:59 +0200 Newsgroups: sci.physics.research Summary: discussion and a number of references Keywords: bicycle, stability, steering, gyroscopic effect, castering In article <200004250531.RAA06538@ssp5-02.math.canterbury.ac.nz>, Bill Taylor (W.Taylor@math.canterbury.ac.nz) wrote: : First, a comment. It's often stated that the gyroscopic effect : of bike wheels is a big help in keeping the cyclist upright. : I doubt it. In article <8eck8e$u6$2@inn.jlab.org>, David McKee replied: > Long ago I saw an aricle on this very topic. It may have been in > Science News. > > The attched photograph showed an ordinary bicycle with extra wheel > mounted above each of the usual ones, and in contact with them so that > they (the extra wheels) were counter-rotating. The text explained that > the bike was very hard to keep upright. On the contrary, gyroscopic effects are of only minor importance in bicycle stability. Zero-net-angular-momentum bicycles of the sort David McKee describe (eg David Jones' URB I, see his Physics Today article cited below), turn out to be easily ridable. The key determinant of bicycle stability is actually the castering of the front wheel, i.e. the placement of the front wheel's spin axis *ahead* of the projected front fork line. [[Note that the above refers to the normal case when the bicycle has a human rider present and steering. Hands-off stability is somewhat different. One can also consider the stability of *riderless* bicycles; Jones' Physics Today article (cited below) discusses this.]] In a series of postings (referenced in this posting's header) in July and August 1993, Leigh Palmer discussed this very nicely (Hi, Leigh, if you're reading this!) and described some experiments he'd made on both no-hands and riderless stability. Notably, in article <1993Aug6.055408.4067@sfu.ca> (5 Aug 1993), he wrote: [[lines rewrapped to be shorter]] # Turning no-hands is a two-shift operation. If you lean to # one side, the bicycle will lean to the other side, and the wheel will # turn increasingly to the other side. Unless you now lean to the other # side, causing the wheel to stop turning increasingly to that side, # you will crash. You must apply corrective weight change to keep the # wheel pointing in the direction you desire. This can be done by the # skilled rider with the lightest (therefore lowest moment of inertia) # wheels obtainable. Angular momentum is a relatively insignificant factor, # though of course it is present. One could in principle demonstrate this # by stiffening one's body and closing one's eyes while riding no hands # in a circle. One would be stupid to attempt this, as others who have # experience riding no hands will readily attest. # # In the case of a riderless bicycle angular momentum is important in # keeping the bicycle moving uniformly in a circle. I've never tried # Experiment #3 with a fancy aero aluminum-rimmed bike with sewups, only # with my old clunker 1947 24-inch clincher Huffy, a forerunner of today's # mountain bikes. References: David E. H. Jones "The Stability of the Bicycle" Physics Today , April 1970, 34-40 Framk Rowland Whitt and David Gordon Wilson "Bicycling Science", 2nd edition MIT Press, 1982, ISBN 0-262-73060-X (paperback), -23111-5 (hardcover) ... this book has a chapter devoted to stability, but my copy is at home at the moment, so I can't quote the chapter number J. Lowell and H. D. McKell "The Stability of Bicycles" American Journal of Physics 50(12), Dec 1987, 1106-1112 G Franke, W Suhr, and F Reisz, "An advanced model of bicycle dynamics", European Journal of Physics 11 (1990) 116-121 John Maddox's report of the Franke/Suhr/Reisz paper in Nature 346, 2 Aug 1990, p 407. -- -- Jonathan Thornburg http://www.thp.univie.ac.at/~jthorn/home.html Universitaet Wien (Vienna, Austria) / Institut fuer Theoretische Physik "I'd like a large order of Fibonachos, please." "Okay, sir...that will be the cost of a small order, plus the cost of a medium order." -- from sci.math ============================================================================== From: see.URL@end.of.post.epfl.ch (Martin Ouwehand) Subject: Re: bicycle stability (was: Re: Motorbike wheels.) Date: 12 May 2000 16:46:51 GMT Newsgroups: sci.physics.research In article <8fb7vf$4od$1@mach.thp.univie.ac.at>, jthorn@galileo.thp.univie.ac.at (Jonathan Thornburg) writes: ] References: [...] There is also a nice chapter on bicycle stability in Felix Klein and Arnold Sommerfeld's great classic "Theorie des Kreisels" (Theory of the Top -- I wonder if it was ever translated into english; anyhow it would be nice to see this work reprinted,, even if it is from the 1890's). -- | ~~~~~~~~ Martin Ouwehand ~ Swiss Federal Institute of Technology ~ Lausanne __|_________ Email/PGP: http://slwww.epfl.ch/SIC/SL/info/Martin.html __________ Les gens superstitieux portent malheur [C. Juvet]