On car steering torques at parking speeds

The steering torque at the handwheel, necessary to steer a car at zero speed, is discussed. Measurements made on a tyre alone on a static rig and measurements made on a car in normal trim are complemented by a mathematical system model. The model uses parameter values deriving partly from the tyre rig results, partly from the car specification and partly from the car results. It provides simulated behaviour matching that from the car experiments. It therefore provides a basis for understanding the results obtained and for predicting the results of design and operating changes. The various physical mechanisms involved in the steering torque are identified and their relative magnitudes, for the case considered, are established. The role of steering offset receives particular attention.