Danger, rear wheel steering

Abstract

Rear wheel steering, which is common in fork lifts and loaders, brings about certain deceptive driving characteristics. The hazards are illustrated with authentic accident case descriptions and are elucidated through analyses of vehicle dynamics.Vehicle stability at every speed requires that the cornering stiffness coefficient of the rear wheels is larger than that of the front wheels. Therefore, rear wheel skidding with attendant overturning risk is more likely to occur: (i) with insufficient rear tyre pressure; (ii) if the front wheels only are studded ; (iii) when a counterweight truck is unloaded.In addition, it is impossible to recover from a rear wheel skid with rear wheel steering. Field tests on ice confirmed that a rear wheel skid is aggravated if the driver compensates for it in the common way by steering in the direction of the skid.Rear wheel steering systems are usually not self-stabilizing. Thus, severe yaw motions may occur unintentionally, if the steering-wheel is held too loosely.Conclusively, rear wheel steering should be avoided for normal driving, e.g. with a turnable driver's cab and automatic speed limitation in one direction. Such a design will also decrease the risks of load loss upon braking and improve frontward view, particularly in fork lifts.