Cars and Motorcycles - Physics for Game Programmers - page 239

Turning a Motorcycle
Turning a car is pretty straightforward. The wheels are turned in the direction of the turn. If you
try to turn in this manner on a motorcycle, except at very low speeds, you will crash the bike.
The reason is an effect called gyroscopic precession . When the wheel of the bike is turned in
one direction, a torque is applied to the wheel in the opposite direction, causing the bike to
lean. In other words, if you turn the front wheel of a bike to the left, the bike will lean to the right
and vice versa. Because of this effect, if you try to turn the front wheel of a motorcycle in the
direction of the turn, you will fall forward off the bike.
■ Tidbit It's easy to demonstrate gyroscopic precession, and the bike doesn't have to be moving to do it.
Stand your motorcycle or bicycle straight up and turn the front wheel 90 degrees in either direction. The bike
will lean in the opposite direction.
The secret to successfully turning a motorcycle at higher speeds is to lean into the turn as
shown in Figure 8-11. This type of leaning stabilizes the motion of the motorcycle during the
turn. There are several ways to get a bike to lean into a turn. The first technique makes use of
gyroscopic precession and is known as countersteering . To initiate a turn, the driver must turn
the front wheel in the opposite direction of the turn. This maneuver may seem strange, but
remember that turning the front wheel in the opposite direction of the turn causes the bike to
lean into the turn. The proper lean can also be created or augmented by having the driver lean
his shoulders into the direction of the turn.
Figure 8-11. To successfully turn, a motorcycle must lean into the turn. (Photo courtesy
of Brett McLeod)
The mathematical equations that describe the forces and moments that exist during a
countersteered motorcycle turn are quite complicated, with various moments of inertia terms
and angular velocities. Unless you are building a very detailed motorcycle simulation, there is
probably no reason to try to include that level of complexity in your game. The way to include