Question

Why does a cyclist bend or lean during a turn?

Answer 1

A cyclist must lean into a turn to prevent tipping over in the other direction. To see why this is so, consider the sketches below. The sketch on the left represents a cyclist, seen from behind, who is attempting to remain upright while turning to the left.

There are three forces acting on the rider and bicycle:

• The weight of the rider and bicycle, W
• The normal force, N
• The frictional force, F

Turning on a cycle requires a net force called centripetal force. The frictional force provides the centripetal force necessary to turn the cyclist to the left. But the frictional force also produces a clockwise torque that will cause the rider and bicycle to tip clockwise to the right. In the sketch, on the right, the cyclist is leaning in the direction of the turn. Now the normal force of the road does not act through the center of gravity. It produces a counterclockwise torque that cancels out the clockwise torque of the frictional force. Thus there is no tendency for the cyclist to tip to the right.