The variable M differential lock significantly improves performance when starting and pulling out on slippery surfaces.
It allows a particularly sporty style of motoring because it minimises the risk of the drive wheels spinning on one side when taking a narrow bend quickly.
Conventional differential locks measure the difference in torque on the two drive wheels: in contrast, the new BMW system operates an axial piston pump which reacts to the difference in speed between the wheels.
This pump then serves to carefully gauge the closing of a multiple-plate clutch connecting the two half-shafts according to specific requirements.
The result is a significant increase in traction compared to conventional differential locks.