Rolling friction is the friction that occurs between two surfaces when an object such as a wheel or a tire rolls.
Rolling friction has much less effect than sliding friction, but that depends to a very large extent on the nature of the materials involved and their condition. For instance, steel wheels on a steel rail produce very much less rolling friction than under-inflated rubber tires on a loose gravel surface. The rolling friction from that combination of surfaces will slow a vehicle down faster than fully inflated tires on a smooth road.
The forces that cause a vehicle to slow down when the brakes are applies are a combination of sliding and rolling friction, even though most of the slowing effect is from the sliding friction. Nevertheless, tires made from materials with high rolling friction characteristics slow the vehicle during normal driving and reduce fuel economy, tires made from materials with low rolling friction improve fuel economy – for instance tires with high sulfur content tend to have lower rolling friction.
