Four wheel steering

Description

Four-wheel steering, 4WS, also called rear-wheel steering or all-wheel steering, provides a means to actively steer the rear wheels during turning maneuvers. It should not be confused with four-wheel drive in which all four wheels of a vehicle are powered. It improves handling and helps the vehicle make tighter turns.

Production-built cars tend to understeer or, in a few instances, oversteer. If a car could automatically compensate for an understeer/oversteer problem, the driver would enjoy nearly neutral steering under varying conditions. 4WS is a serious effort on the part of automotive design engineers to provide near-neutral steering.

The front wheels do most of the steering. Rear-wheel turning is generally limited to 50-60 during an opposite direction turn. During the same direction turn, rear-wheel steering is limited to about 10-1.50. When both the front and rear wheels steer toward the same direction, they are said to be in phase and this produces a kind of sideways movement of the car at low speeds. When the front and rear wheels are steered in opposite directions, this is called anti-phase, counter-phase or opposite-phase and it produces a sharper, tighter turn.