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Name: Justin
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Question:
I was recently at a public lecture at the University of Michigan, and one of the physicists, in a side comment, said that the spinning of bicycle wheels did not change the stability of the bicycle. He cited some recent article. How can this be?



Replies:
New Scientist addressed this several years ago in the article below. The gyroscopic forces are quite small. The stability is mostly due to the fact that if you lean, say, to the right, the bike steers to the right, which puts the wheels back under your center of gravity. It is a somewhat self-correcting mechanism. The author built a bicycle with counter-rotating rotor to cancel the small gyroscopic effect and found it to be equally stable. Another author references a "skate-bicycle" that is also stable without benefit from rotating wheels.

http://www.newscientist.com/article/mg19225812.400

More math here... "A Bike with Reverse-Spinning Wheel"

http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm

Paul Bridges



Check out

http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm

for a detailed explanation of bike stability.

It says " Gyroscopic forces are not important for the stability of a bicycle ... but they help us to control the bike when riding with no hands. More important than anything is "the trail". The front wheel makes contact with the pavement at a point that lies behind the point where the steering axis intersects with the pavement - and the distance between these is called the trail. The trail is not zero because the steering axis is tilted and the front fork is bent. The trail works to stabilize a bike in much the same way as castors work on a tea trolley. When you lean to the right, say, on your bicycle force at the contact point on the pavement will push the front wheel to the right. This helps you to steer effortlessly and it allows for hands-free steering through leaning slightly left or right. The gyroscopic effect helps but the trail is the more important factor."

David S. Kupperman


Here is a definitive reference.

http://socrates.berkeley.edu/~fajans/Teaching/bicycles.html

and perhaps this (not recent) article is the one to which he refers?

http://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdf

Burr Zimmerman


Considering the lightness (masslessness?) of racing bicycle rims and tires, the effect is minimal for someone like Lance Armstrong.

R. W. "Bob" Avakian
Instructor
B.S. Earth Sciences; M.S. Geophysics
Oklahoma State Univ. Inst. of Technology



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