Lateral force and slip angle

The term “Slip” in slip angle and slip ratio is a misnomer. In reality there is very little slipping going on, its more like stretching and then releasing. For a tyre to produce a lateral force, the tyre is distorted as it rotates through the contact patch. A simple representation of this is shown in the diagram. Essentially the tyre’s slip angle is the angle between its directional travel and its direction of rotation. The red line represents the lateral deformation from its unstressed position. It’s the tyres resistance to this deflection that produces the lateral force.

Lateral force and slip angle - White-Smoke

The three dimensional visualization of Lateral Force with Slip Angle and Normal Load is shown in the diagrams. The chart on the left is for pure lateral force (zero slip ratio). The chart on the right is for -5% slip ratio.

Lateral force and slip angle - White-Smoke

The importance of looking at tyre data and it's analysis as a response surface and not just as a two dimensional representation, can clearly be shown from these charts. Response surface methodology (RSM) is an invaluable tool when validating tyre data. It gives a complete tyre performance envelope picture for given set of parameter inputs. As we will see later, trends and optimization of parameters can be obtained quickly, as humans are extremely apt at assimilating three dimensional shapes in this way. The curvature of the surface and its changes in shape as the input parameters change is what makes chassis tuning possible. It is the understanding of how these characteristic changes in the tyres response effect the car in motion that provides the foundation of vehicle dynamics.

< Previous | Next >

More pages