Motorcycle Turning

Question: If you are on a motorcycle going down the highway, and you press 
on the inside of the left handle grip, why do the wheels turn to the right, 
but you turn to the left?
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1991: This only happens, by the way, above a certain speed.  If you are 
going slow enough, the bike will turn in the direction you would expect.  The 
reason the motorcycle behaves as you describe at speed is due to a phenomena 
called precession.  For a thorough explanation of precession, I recommend you 
look it up - it is a fairly complex subject.  You can observe precession with 
a gyroscope.  I will give you a quick explanation, though.  When you try to 
turn a rotating object, you produce a force at 90 degrees to the direction of 
rotation.  When you push on the left handlebar and turn the front wheel of the 
bike to the right, you produce a force which makes the whole motorcycle lean 
to the left.  It is the leaning to the left that turns the bike.
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Update: 12/14/2004
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Gyroscopic precession is one of two factors that cause the cycle to turn opposite the 
direction the handlebars are moved. A great explanation of precession is given in a 
book called "Thinking Physics" by Lewis Epstein. However, the precessional force 
acting to tilt the wheel left when you move the handlebars right, is diminished
by the fact that the front forks are not vertical, but angled forward. To exaggerate 
this, imagine that the front forks were completely horizontal. Turning the handlebars 
right would simply cause the wheel to tilt right, but precession would cause the 
wheel to try to angle right as viewed from above. Here now, would be a tendency for
the front wheel to track to the right, as wanted. This fact is apparent in choppers
which have long front forks. A second major force occurs when the wheel is deflected. When a 
cycle leans left or right, it tilts about a pivot point where the tires
contact the road. If the wheel is forcefully deflected to the right, the wheel will
immediately begin tracking to the right (slightly) even though precession
makes the wheel lean left. As the cycle begins this slight change in direction (to the right),
centrifugal force immediately throws the bike and rider to the outside of the turn, 
making it tilt about its pivot point, and lean to the left. Once you lean left,
you're going left. 

T. Esposito
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