[darkmcs]

From http://www.canadiandriver.com/2009/0...28i-xdrive.htm :

"In the 3 Series, xDrive routes all power to the rear wheels until they start to slip; when that happens, as much as half the engine’s torque can be sent to the fronts. The system’s benefits are most obvious in snowy weather, where it reacts quickly to provide traction. In dry conditions, of course, its operation is more subtle and shines through best when accelerating out of a corner. Where a rear-wheel drive 328i would try to spin the inside rear tire in that situation, only to be stifled by the traction control system, this car’s front wheels get in the game and help pull the car through."

I thought X-Drive was 40:60 in normal driving and could shift as much as 100% to one axle (as opposed to 50% stated in this article)...

[Amdahl]

The article is (mostly) wrong on the default split. The default split is 40:60. The car can do a 0:100 split, so it is possible that at certain times, it is doing so.

As for torque ranges, in the other thread, it is assumed to be that you can do 100% to the rear, but maximum 50% to front with 50% to rear. Nobody seems able to find anything in print that says you can do 100% to the front -- they just are very vague on that.

[darkmcs]

Originally Posted by Amdahl

The article is (mostly) wrong on the default split. The default split is 40:60. The car can do a 0:100 split, so it is possible that at certain times, it is doing so.

As for torque ranges, in the other thread, it is assumed to be that you can do 100% to the rear, but maximum 50% to front with 50% to rear. Nobody seems able to find anything in print that says you can do 100% to the front -- they just are very vague on that.

Thanks for the reply!

As far as transferring 100% to the front, I don't think it is possible.

A quick "real-life" example from this morning:

Yesterday, we were hit with a few inches of snow. As this time of the year, I had my summer tires on. My driveway is very steep and there was a patch of deep snow for the first foot of so... I stop with my front wheels on the snow and the rear wheels on the wet. The power transferred immediately and there was no spinning from the front wheels. I then stopped with the rear tires on the snow and the front tires on the wet concrete tiles of my driveway. (keep in mind it's a very steep uphill driveway) The front tires had some grip but the rear tires spun a little before the car moved forward... (I'd say less than a second)

This little experiment led me to think that it is probably true that xDrive can go 0:100 but only 50:50. The rear wheels always get at least 50%...

This is, of course, to my humble understanding of this AWD system!