4WS is an abbreviation for 4 Wheel Steering, which is a device with which the direction is changed not only for the front tires but for the rear tires as well. When changing the direction of the vehicle, a normal vehicle turns only the front tires, but a 4WS vehicle also turns the rear tires according to such factors as the angle the steering wheel is turned to and the vehicle speed. At medium and high speeds, when changing lanes, negotiating an S curve, or cornering, the rear tires move slightly in the same direction as the front tires for smooth, stable driving. On the other hand, when the vehicle does not have much speed, the rear tires are steered the opposite direction from the front tires for sharp turning.