Portal:Physics/Selected article/Week 13, 2007

A simplified mathematical model of bike and rider.

Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles. It is concerned with the motions of bikes, their parts, and the forces acting on them. Specific subjects include balancing, steering, braking, and suspension.

Experimentation and mathematical analysis have shown that a bike stays upright when it is steered to keep its center of mass over its wheels. This steering is usually supplied by a rider, or in certain circumstances, by the bike itself.

While remaining upright may be the primary goal of beginning riders, a bike must lean in order to turn. The higher the speed or smaller the turn radius, the more lean is required. This is necessary in order to balance centrifugal forces due to the turn with gravitational forces due to the lean.

When braking, depending on the location of the combined center of mass of the bike and rider with respect to the point where the front wheel contacts the ground, bikes can either skid the front wheel or flip the bike and rider over the front wheel.