Originally Introduced on the BMW 7 Series, Automatic Stability Control + Traction (ASC + T) is a BMW only feature which is a suspension control system that help reduce engine output by making sure that the vehicle can move or acceleration can take place, without wheelspin.
This system can kick in regardless of how the car is being driven. If the reduction in acceleration is not enough, each drive wheel is braked individually until both wheels have optimum traction. Braking is under control of the BMW pioneered Anti-lock Braking System (ABS) system.
How does it work:
In critical situations on the road, the angle of the throttle butterfly in the ignition system is altered in such away as to allow only the maximum transmissible power to reach the wheels, while Digital Motor Electronics (DME) adjust the ignition time. This results in the drive force being cut back by up to 50 per cent. In addition, ASC+T will also activate the brakes in the rear wheels if necessary, and to varying degrees if frictional coefficients on the road differ.
The ASC+T system knows when stability and traction have to be increased thanks to the ABS sensors, which provide the computer with a steady stream of data on wheel slip for each side of the car, as well as on changing speeds in the drive wheels. If the predetermined limits are exceeded, the control unit will instantly activate the traction system.
All the driver registers of this complex procedure is a decrease in engine torque despite the fact that pressure on the gas pedal may not have changed. Also, a control lamp in the instrument display will come on to indicate that ASC+T is in action and that the driver should adapt to the altered road surface. Source
Benefits of the Automatic Stability Control and Traction (ASC-X):
* Excellent safety on wet road surfaces (rainy, ice, snow, loose gravel)
* System is quick to act and can detect even slight surface changes
* Blocking of wheels no longer occurs occurs when the accelerator is released on a slippery surface