3 - Wheel travel and elastokinematics

Abstract

Kinematics'—wheel travel, often also called wheel (or steering/suspension) geometry—describes the movement caused in the wheels during vertical suspension travel and steering. Whereas, ‘elastokinematics' defines the alterations in the position of the wheels caused by forces and moments between the tyres and the road, or the longitudinal movement of the wheel, against suspension anchorage required to prevent compliance, kinematic changes. The changes are the result of the elasticity in the suspension parts. To ensure the required road holding and directional stability and to prevent excessive tyre wear, automobile manufacturers specify certain settings, including the permissible tolerances for the front axles of all models and for the rear axles, provided these are not driven rigid axles. The wheelbase l, measured from the centre of the front to the centre of the rear axle, is an important variable in the vehicle's ride and handling properties. A long wheelbase relative to the overall length of the vehicle makes it possible to accommodate the passengers easily between the axles and reduces the influence of the load on the axle load distribution. The handling properties of a vehicle, both in the steady-state as well as the transient region, are determined by the kinematics - the change in position of the wheel during travel or roll movements of the body - and the elastokinematics - the movements of the wheel with longitudinal or lateral forces in the tyre contact area - of the wheel suspension. As even slight changes in the position of the wheels can have a big effect on handling properties and the wear and tear of tyres, particular importance is attached to the accuracy of the measuring technology used and a precise knowledge of the way in which control of the wheels depends on forces and movements.