Rolling Resistance

Consider a tire rolling at a constant speed. Forces acting on it are its weight and the normal force.

The contact surfaces deform, creating a finite contact area. This results in a distribution of normal forces at each contact point.

The front section of this area experiences deformation, which retards the rolling motion.

In contrast, the rear section undergoes a relatively smaller restoration that pushes the tire forward.

The resultant normal force acting at A is the sum of these forces.

To keep the tire rolling at a constant speed and balance the moment of the weight about A, a horizontal driving force must be applied to the center of the tire. Here all the forces must be concurrent.

The moment equilibrium condition at point A gives the driving force in terms of the coefficient of rolling resistance.

The weight multiplied by the coefficient of rolling resistance upon the radius is usually smaller than the coefficient of kinetic friction times the weight.

So, the rolling frictional force is smaller than the sliding force.