[CSBM5]

Originally Posted by CanAutM3

Actually he does explain it fairly well, albeit in very technical terms. What I understand is that the two output shafts are designed with a different stiffness to minimize harmonic behaviour in lower traction conditions; read reduce axle hop.

This was first implemented over 10 years ago by Cadillac in the CTS-V, so it's nice to see BMW finally getting around to it. Cadillac were the first to finally put a damper (pun, lol) on the IRS "axle-hop" dynamic problem. It's a ridiculously complicated non-linear dynamics problem with many different degrees of freedom. We've all felt it when accelerating hard in an IRS car and one gets the stuttering wheel hop shaking. There is a "wind up" of energy when the tire has grip that eventually (talking in very short timeframes here) is unleashed causing the tire to break traction only to then recycle with another wind up cycle, etc, etc.

Cadillac discovered that if they employ the proper ratio of torsional stiffness between the two IRS half-shafts (based on that huge number of variables overall dynamics problem), they can allow for absorption/release (so to speak) of said energy and greatly reduce the cyclic build-up/release cycle. Said design was first on the gen2 CTS-V but then also shared with other GM cars with an IRS.