Brake Steer is a variation on McLaren’s electronic driver aid used successfully in
Formula 1 on the 1997 McLaren MP4-12. It was subsequently banned, indicating its clear performance advantage, but has been developed for the 12C as the control system to prevent wheel spin and
Brake Steer does essentially the same job as a ‘torque-vectoring’ differential, but is up to 20 kgs lighter – part of the 12C’s ‘weight-down’ design philosophy. It uses the same hardware to operate as the 12C’s Electronic Stability Control (ESC) system, preventing wheel spin, reducing understeer, and significantly boosting track times.
In essence, it is a system that applies braking forces to the inside rear wheel when the car is entering a corner too quickly to make the desired radius – supporting either a driver who has misjudged the corner, or a skilled driver seeking the fastest possible entry and exit from a corner. Under normal circumstances these scenarios would tend towards a state of understeer. Brake Steer controls this and makes the car behave in a more neutral fashion, bringing its nose back on line. It assesses the steering angle to determine the driver’s intended course and applies the inside rear brake to increase yaw rate and resume the desired course.
The system also works on acceleration out of a corner when the inside rear has a tendency to spin, allowing the driver to put power down more quickly.
The 12C’s ESC system is managed electronically by the driver-operated Active Dynamics Panel settings. The 12C provides ample grip and safety in ‘Winter’ or ‘Normal’ modes, yet ESC offers increased slip in ‘Sport’ or ‘Track’ modes.
A unique McLaren Airbrake adds drag and rear downforce when deployed under braking, helping the car to decelerate and meaning more rear brake pressure can be used, hence stopping distances are shortened.
Adding rear downforce also improves the car’s stability under braking to give a more secure feel and optimum track performance: under typical heavy braking, the rear can go ‘light’ as weight is transferred forwards, ‘pushing’ the front of the car down. With an Airbrake, the car behaves as if ‘pulled’ from behind, counteracting the tendency to dive, therefore maintaining traction.
Under heavy braking above 95 km/h, a piston operated by transmission hydraulics raises the Airbrake to 32 degrees. Once the first stage ‘wing angle’ is set, and the Airbrake pushed into the airflow, the centre of aerodynamic pressure forces the bottom of the ‘wing’ back up to 69 degrees: aerodynamics raise the Airbrake to its full and maximum angle rather than relying on a larger, and therefore heavier, motor. This weight-saving solution took almost 50 per cent of weight out of the mechanism.
Source: Official press release - February 14th 2011.