Four-wheel Steering (4WS)
Four-wheel Steering (4WS) The front-to-rear wheel alignment plays a significant role in the directional stability of a vehicle. Often the lack of stability causes a dangerous drive. This is clearly observed when a car has worn suspension bushes. Up to the mid-1950s the majority of cars suffered from over-steer, mainly due to the uncontrolled movement of the rear axle caused by spring deflection which is initiated by body roll. The problems associated with an over-steer characteristic are now well understood. To improve stability, most cars nowadays are designed to exhibit under-steer characteristic when driven at high speeds. One step in obtaining an under-steer characteristic is to use body roll movement to steer the rear wheels. This is achieved either by misaligning the rear axle or by changing the geometry of the suspension system in the case of the car fitted with independent rear suspension. Although under-steer condition improves stability of the vehicle, it increases the driver