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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > xDrive, Power Distribution and VDC



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      12-16-2011, 10:53 AM   #1
undisclothesed
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xDrive, Power Distribution and VDC

Just bought a 335i xDrive 6mt w/ msport and I love the car so far! I did a few quick searches but couldn't find any solid answers.

Please correct me if I'm wrong. From what I've read xDrive only distributes power between the front and rear axles (not individual wheels). Also, 100% of the power can be distributed to either the front or rear axle.



How does VDC effect xDrive when it's turned off?

Does the car run w/ 100% of the power to the rear wheels (or fronts) by default?


Are there any other traction control features in the car beside VDC?
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      12-16-2011, 04:00 PM   #2
Doyle
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Yes, both axles have open differentials with "e-LSD". Therefore power can only be distributed f/r. That is up to 50% torque and 100% available power.

Not sure what you mean by VDC. If you mean the DTC, then the transfer case will split power just like it would if it was on. From my experience, DTC cuts power when it is on. When it is off, power stays on, but the TC still optimizes available traction.
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      12-16-2011, 06:20 PM   #3
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No more than 50% to the front, rear can have 100%.
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      12-18-2011, 10:43 AM   #4
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Sorry I wasn't clear, by VDC (Vehicle Dynamic Control) I actually meant DSC (Dynamic Stability Control).

VDC is activated on the car by default. By pushing the VDC button on the dash the car will enter VTC mode which is similar but allows more wheelspin. Holding the VDC button for 5 sec. will deactivate VTC and VDC.


Which wheels power the car by default when there is no wheel slippage in an X-drive car?

How does the X-drive system sense how to distribute power between the front and rear axles?

How does VDC and VTC affect the X-drive system?

How does de-activating VDC/VTC affect the X-drive system?


I want to believe:
-When there is no wheel slippage X-drive behaves similar to a RWD car (100% power to rear wheels, all the time)
-When VDC/VTC are turned off the car will drive 100% rear wheels only by default regardless of wheelspin

..but I believe with xDrive in the middle it's more complicated than that.

Last edited by undisclothesed; 12-18-2011 at 10:49 AM.
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      12-18-2011, 11:43 AM   #5
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Lol @ "I want to believe"

Every "aggressive driving" situation I have been in (autox, HPDE, etc) I have turned VTC/VDC off entirely. X-drive behaved normally, but there was no power cut.

For example: My first run at an autox course, I left stability controls on. There was minimal wheel slippage, but the traction controls pulled tons of power when there would have been traction loss. It felt like bogging a shift. However, on my next run, I turned everything off. On that run, wheel slippage was allowed, but the only response the car had was through redistributing the torque to either axle. I doubt that the car started out in RWD mode. But it wouldn't have mattered, since when I got the tiniest bit of oppo, x-drive interfered and sent power to the front.

TLR - x-drive cannot be turned off through any of the stability controls.

However, there are some individuals that are looking at a solution, right now
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      12-20-2011, 10:00 AM   #6
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From what I've read on the forums, xDrive maintains a normal 40/60 split between F/R in normal conditions, and adjusts those values when slippage occurs. Over a certain speed (highway travel), I've heard the vehicle becomes full RWD.
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      12-20-2011, 12:52 PM   #7
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Quote:
Originally Posted by panzerfaust View Post
From what I've read on the forums, xDrive maintains a normal 40/60 split between F/R in normal conditions, and adjusts those values when slippage occurs. Over a certain speed (highway travel), I've heard the vehicle becomes full RWD.
+1 there is another thread regarding this so ...but I believe it was over something like 60 or 65mph it becomes full RWD
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      12-20-2011, 01:40 PM   #8
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Quote:
Originally Posted by MakkkD View Post
+1 there is another thread regarding this so ...but I believe it was over something like 60 or 65mph it becomes full RWD
112mph according to this guy, I've always heard ~100mph so I have reason to believe that.

http://www.e90post.com/forums/showpo...&postcount=297
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