FSI Power

the rear wheels until the electronics detect wheel spin and then power is directed to the front wheels?

Tanner

Though from Wikipedia they say 40% front, 60% rear:

<I>BMW xDrive, BMW's all wheel drive system that powers the X3, X5 and 2006 and later xi 3-series and 5-series models.

Instead of a 60-40 (rear-front) power split (which all millennium 4 wheel drive BMW's exhibit - 325xi, 330xi, early X5) with power being cut to wheels which lost traction through DSC (Dynamic Stability Control), xDrive allowed both of these vehicles to split power between the front and rear axles through use of a multiplate clutch located between the gearbox and the Cardian shaft. This setup allowed xDrive vehicles to split power in virtually any way it pleased. If the car felt like it was it was in a threatening situation (note not an unstable one), xDrive would react immediately, often before the driver ever knew of its intervention, to alleviate traction and control of the vehicle.

xDrive is also closely knit with DSC. In the case that wheelspin stills occurs while xDrive is or has been shifting power, DSC can brake independent wheels to regain traction. xDrive also helped in cornering. When the vehicle felt it was about to understeer or oversteer the vehicle would cut traction to either of the front wheels or rear wheels to help regain stability and keep the driver on the road.

xDrive was one of the first technologies used to intervene before the driver was apparent that the car could ever be unstable. Its intervention is transparent to the driver. </I>

FSI Power

describes the older xi ("millenium") AWD BMWs.

This is what keeps me awake at night...