I believe the pre-xDrive vehicles have a transfer case that directs the power 38F/62R full time. Nothing at all can be done to alter this software-wise, this is purely mechanical.

I think (?) the xDrive vehicles have a clutch pack in the transfer case that will allow power to be directed front to rear. I don't know if this system could handle throwing 100% power to the front, or if there is anybody with a program able to attempt such a feat. Either way, your X5 will still have open differentials and won't be as sure-footed in the snow as a Subaru.

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