Quote:
Originally Posted by snowbimmer
Great points, guys. It seems there would be some favorable tolerances built into the BMW 4WD systems, because there are thousands of folks here on the forums changing their rides from OEM tires and wheels to aftermarket products. (Granted, 2WD much less critical, so G8x M3s and M4s are newer to the game). I only seem to read about people with rubbing problems and strut clearances, which they fix, but never any differential problems (unless they just keep quiet  ). |
Latest xDrive systems have been greatly revised, compared to the original designs, back in the days of models like the E83 X3. On those models tire tolerances were very critical and many transfer cases were compromised/destroyed with generic tire fitments. (Personal experience, my local tire shop would only fit star marked tires to the E83 X3, due to too many drivetrain issues with non approved fitments).
Transfer cases in the current M models have much more 'RWD only' engagement. The BMW M VTG control only applies torque to the front axle/wheels in limited situations. This means the multidisc clutch is running open much more of the time. This at least partly explains how BMW can be more flexible with M model tire selection.
Even in the more regular models, there are technical features to improve heat management and reduce wear. Plus changes to oil levels and flows, which reduce churning losses, aids efficiency.