This is achieved by utilising a torque transfer differential which is controlled by various sensors and an electronic control unit (ECU) to enable a difference in torque to go to each of the rear wheels.

As shown in diagram 1 (right hand bend), by increasing the level of torque to the left rear wheel and reducing the torque level to the right wheel, it is possible to change the yaw movement of the vehicle. This in turn will cause the vehicle to steer inwards and reduce the amount of slip on the front tyres, thus resulting in reduced under-steer. It also works if over-steer occurs, as shown in diagram 2, by reducing the torque level to the left hand rear wheel and increasing the torque level to the right hand wheel, again changing the yaw movement to reduce over-steer.

By controlling the amount of torque transmitted to the rear wheels when there is less traction, or a difference in grip on the road surface, AYC also works to improve acceleration and stability on slippery roads (as shown in diagram 3).

Active Centre Differential

The Active Centre Differential, first introduced in the Evo VII, is an electronically controlled hydraulic multi-plate clutch which distributes torque between the front and rear to improve traction under acceleration out of a corner. It works in conjunction with Active Yaw Control which enhances grip and steering response whilst driving through the bend itself. Using sensors, ACD regulates slippage in the 50:50 torque-split diff from free to lock-up according to speed and load. So under hard acceleration the ACD moves towards lock-up to put more torque down on the road for stronger traction, but with rapid steering inputs it operates virtually like an open differential to improve steering feel and response.

A choice of three setting - tarmac, gravel and snow - operated manually, gradually lock up the Active Centre Differential depending on road conditions.