The new Mercedes-AMG SL: the active rear-axle steering

Oct 28, 2021

For the first time in its long history, the SL is equipped with active rear-axle steering as standard. Depending on the speed, the rear wheels steer either in the same or in the opposite direction as the front wheels. The system, which is precisely tuned to the new SL, thus enables both agile and stable handling. Other advantages include easier vehicle control at the limits and less steering effort because the front-wheel steering ratio is more direct at 12.8:1 (instead of 14.2:1 without rear-axle steering).

At the heart of the system are two electromechanical steering actuators (electric motors with spindle drive) that have no mechanical connection to the steering wheel. They replace the conventional control arms on the rear axle. This "by-wire" system adjusts the rear wheels within a predefined characteristics map by means of electronic control. The toe angle change is up to 2.5 degrees in one direction at the rear wheel.

Up to a speed of 100 km/h, the rear wheels turn in the opposite direction to the front wheels. This corresponds to a virtual shortening of the wheelbase. Advantage: The SL is much more agile when turning into bends, making it even more fun to drive and requiring less steering effort. Further benefits include increased manoeuvrability and a smaller turning circle in everyday driving situations ‑ such as when making a turn or parking.

If the SL is travelling faster than 100 km/h, the system turns the rear wheels parallel to the front wheels (maximum steering angle then 0.7 degrees), corresponding to a virtual lengthening of the wheelbase and improving handling stability. At the same time, the lateral force on the rear wheels builds up considerably faster on changes of direction, thus speeding up the response to the steering.

The active rear-axle steering not only improves cornering, it also assists the driver in the event of sudden evasive manoeuvres and thus enhances active safety, making the SL easier to control at the limits.

The response is also dependent on the AMG DYNAMIC SELECT driving mode: In Sport+, for example, the rear-axle steering reacts even more agilely and directly at lower speeds. It also assists with optional automatic parking and the Remote Parking function. Later updates "over the air" are also possible.