1.3 Components of the Suspension System
1.3.1 Tires
In the following section, the vehicle tire is considered only from the technical point of view of the suspension and damping. Further representation of the characteristics of vehicle tires can be found in chapter 2.2, where the transverse characteristics of the tire are described, e.g. the generation and transfer of side forces.
Tire as a Spring
The wheel load is transferred to the tire by the rim and pressure is applied to this contact area. The reaction force, which opposes the load on the tire, consists of different components. The figure shows the proportions of the load carrying components of a tire as a function of compression.
The component I corresponds to the proportion of the load carrying capacity of the solid rubber fabric body, due to elastic deformation. The component II represents the so-called circular retaining force of the compressed air, which reinforces the tire in its walls (balloon effect). The component III represents the very small proportion of the air compression.
The component IV represents the principal part, which is based on the adaption of the road contact area A to the vertical load Gw:
Gw ≈ pi ∙ A
(with pi representing the inflation pressure, which implies that the pressure in the tire contact area A corresponds to the inflation pressure.)
Due to the tire compression, an oscillatory subsystem develops in the wheel or in the unsprung masses. In this way, the spring characteristic of a tire influences natural frequency of the wheel or axle.