The same feature was touted for the original M2, but it was referred to as "carbon friction lining" whereas now it says "carbon-fiber friction lining". Unclear how this has been updated, if at all compared to the outgoing model. Both seem to indicate it enhances shifting comfort, whatever that means.
Page 35 of
2015 M2_Technical_Training_INT.pdf
4.2.1. Manual gearbox.
• Improvement of the shifting comfort thanks to use of new type of
carbon friction lining at the synchronisation units.
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Page 6 of
The new BMW M2 Competition - Longversion
Choice of two transmission variants.
The new BMW M2 Competition comes as standard with a six-speed manual gearbox, which stands out with its compact design and low weight. The use of a new type of
carbon-fibre friction lining enhances shift comfort. An engagement speed control function, which blips the throttle on downshifts and lowers the engine’s revs on upshifts, makes gear changes even smoother. This also lends the car additional stability during hard driving on the track. Switching off the DSC deactivates the engagement speed control function. Wet-sump lubrication prevents any sloshing of the transmission oil and ensures all components benefit from an efficient supply of oil.