Tightening emissions regulations have forced BMW to change the propshaft material for its M3 and M4 models.

The M3/M4 propshaft is currently made from carbonfibre, one of a number of carbon components that help keep kerb weight to just 1497kg for a manual M4. In comparison a Mercedes-AMG C63 S Coupe weighs 1725kg, though a fairer comparison is a DCT-equipped M4 which is 1537kg.

Future emissions regulations have required BMW fit a new petrol particulate filter which leaves insufficient space for the current-diameter propshaft.

2018 BMW M4 propshaft change

The forthcoming M4 CS will retain a carbon propshaft as its higher 600Nm torque figure requires the thicker-diameter propshaft and its production run is expected to be completed prior to the new regulations coming into effect.

2018 BMW M4 powertrain changes

Total deliveries of the current-generation M3 and M4 have now topped 68,000 and Australian sales are likely to score a boost towards the end of 2017 with the arrival of the exclusive CS and cut-price M3 and M4 Pure models.