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Bicycles and Gyroscopic Forces
Name: Justin
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
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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Update: June 2012
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