If a wheel rolls under the influence of a side force, mostly during cornering but also caused by side wind or inclined road surface, an angle results between the direction of motion of the wheel and the plane of the wheel. This angle is called the Slip angle (see lecture "AE II"). The vectoral representation of the forces acting on the wheel is shown in the figure above as an example for the influence of the centrifugal force during cornering. The centrifugal force acts perpendicular to the direction of motion, while the rolling resistance towards the plane of the wheel. The lateral force on the other hand, acts normal to the wheel plane because of the slip angle α.
The force of resistance counteracting the direction of motion results from the corresponding components of the lateral force FS and the rolling resistance FR roll.
The right-hand side of the equation can be paraphrased in a way that the resistance share can be immediately seen from the slip angle.
Referring to the wheel load and as a result of the slip angle we obtain the wheel resistance coefficient.
Considering the rolling resistance for uninterrupted straight-ahead drive, since the lateral force FS in the case of negligible slip angles increases in proportion to the slip angle.
In the case of small angles (cosine≈1), the wheel resistance coefficient can approximately be understood as a constant multiplied with the square of the slip angle.