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5
Tyre characteristics and modelling
5.1 Introduction
The handling performance and directional response of a vehicle are greatly
influenced by the mechanical force and moment generating characteristics
of the tyres. In road vehicle dynamics the manner in which a vehicle accelerates,
brakes and corners is controlled by the forces generated over four
relatively small tyre contact patches. If the tread pattern and the road
texture are also considered it is clear that the area of frictional contact
is reduced even more significantly. Figure 5.1 shows the deflection of a
vehicle’s tyres under hard cornering and helps to illustrate the significant
requirements on the tyre to produce forces that control the relatively large
mass of the vehicle.
It is not intended here to discuss the construction of the tyre carcass, materials
or tread pattern. This is addressed by more general texts on vehicle
dynamics (Gillespie, 1992) or more focused books on the subject of tyres
(French, 1989; Moore, 1975). Rather this chapter will start by describing
the mechanisms required to generate the vertical tyre forces that support
the vehicle, the longitudinal forces required for driving and braking and the
lateral forces needed for cornering. The distribution of pressure and stress
will also generate local moments acting at the tyre contact patch. A good
Fig. 5.1 An example of tyre deflection under hard cornering (courtesy of Auto
Motor und Sport)