What exactly causes rolling restistance?

Tyres are deformed by the action of such forces as the weight of the vehicle. This affects the road contact area and the adjacent side wall of the tyres.

When the wheel turns, weight is constantly being applied to and removed from a new section of the tyres. The periodic deformation of the tyre leads to the ongoing conversion of some of the mechanical energy into heat.

The purpose of the energy provided by the engine is to drive the vehicle. Some of this energy is, however, lost by friction in the bearings, by the air resistance of the vehicle and, finally, by the rolling resistance of the tyres.

The heat generated on the rolling tyre varies between the different areas. It is highest in the tread and the belting. If the flexibility of the tyre is reduced by increasing the air pressure, the rolling resistance level decreases too. There are limits to this, however, because a large increase in air pressure reduces driving comfort and driving safety drops when the road contact area of the tyre is smaller.

Optimisation of the tyre design, e.g. by reducing tension in the various components, and, in particular, the formulation of the rubber blend are crucial ways to lower rolling resistance.