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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > xDrive All-Wheel Drive Discussions > Confirmation of xDrive's rear-bias (sort of)
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      11-15-2021, 03:51 PM   #1
LYTSOUT
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Winter is quickly approaching so I'll need decent tires for the midwest snow. However, I've noticed the rear end of my F30 xDrive getting a bit loose in the wet recently which got me thinking about new tires (b/c if they can't handle wet, they definitely won't handle snow).

Upon doing some research, I learned that the imprinted "DWS" on the Conti DWS06 isn't just for show, it's actually functional. The S is imprinted the shallowest, followed by the W, and lastly the D which is deepest. Conti claims that when the S disappears, the tires are no longer good for snow, when the W disappears they're no longer good for wet, and when the D disappears, they're basically toast.

Attached is a pic of the rear. You can see S is completely gone, the W is only barely there, and the D is fine. That confirms that these tires are definitely not gonna work through the winter.

Also attached is a pic of the front. All four tires were installed at the same time (3y and 20k miles ago) and you can clearly see all three letters, DWS, plain as day on the front...so I guess this (sorta?) confirms the rear-bias of the xDrive system!
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      11-15-2021, 05:00 PM   #2
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It absolutely confirms that you should have rotated your tires.
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      11-15-2021, 06:10 PM   #3
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Quote:
Originally Posted by Billfitz View Post
It absolutely confirms that you should have rotated your tires.
Ha! But they're staggered so not rotatable.
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      11-17-2021, 10:22 AM   #4
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I've read it's adaptable in a sense of power distribution but generally and 60/40 rear bias?
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      11-17-2021, 12:50 PM   #5
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It puts power where it's needed. Most of the time that's 40 front/60 rear, but when it detects slip in the rear it sends more to the front.
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      11-17-2021, 09:37 PM   #6
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My 340ix definitely gets squirrelly in the back with the reaction all the way off and I love itů my tires are pretty much bald too so that helps 😅
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      11-18-2021, 09:06 PM   #7
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Agreed! It can put 100% power to the back when needed, and my rears do have a bit more wear than the fronts as well.

Here is a post that has a quote about it:
https://f30.bimmerpost.com/forums/sh....php?t=1129780
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      12-08-2021, 08:17 AM   #8
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Hello, this is my second post in the forum. I have to make some posts to earn my right to access PM. I didn't want to post 'whatever' so I decided to write up a little about xDrive.
BMW F30 rear wheels are always driven. The power is always sent from transmission through the rear driveshaft (2.) to the rear differential and then to the rear wheels.
However the front wheels on F30 xDrive are powered through a transfer case: transmission -> transfer case -> front driveshaft (3.)-> front differential -> wheels.
The clutchpack (5.) in the transfer case is controlled electronically.
When the clutchpack is fully engaged the front and rear drive shafts gets (almost) the same torque from the engine.
BUT depending on the road conditions it can theoretically have 100/0 split f/r torque to move the car in a situation when rear wheels are on ice and only the fronts has traction. In understeer situations clutchpack disengages, front wheels loose torque and car dynamics change to oversteer (rear wheel driven).
BMW claims that xDrive is almost always engaged, but since the clutchpack always has some slip and the rear is directly connected the ratio is about 40f/60r.



If you want to see innards of a transfer case here's a link to a rebuild by kdog_x
https://f30.bimmerpost.com/forums/sh....php?t=1426356

Most of the time the xDrive is controlled nicely but sometimes I feel it holds the front engaged too long. In winter I like to enjoy drifting and "doughnuts", but sometimes when I want to spin 180 while moving it goes forward more that I expect, until the front disengages and lets you spin around.

P.S. The shaft from transmission (1.) goes through the center and is connected to the rear driveshaft (2.) and the housing (9.) of a clutchpack (5.) is always spinning. Only when the clutchpack engages the power is transferred to the gear (5A.) to drive the front driveshaft.
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      12-08-2021, 11:43 AM   #9
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Quote:
Originally Posted by clutched View Post
Hello, this is my second post in the forum. I have to make some posts to earn my right to access PM. I didn't want to post 'whatever' so I decided to write up a little about xDrive.
BMW F30 rear wheels are always driven. The power is always sent from transmission through the rear driveshaft (2.) to the rear differential and then to the rear wheels.
However the front wheels on F30 xDrive are powered through a transfer case: transmission -> transfer case -> front driveshaft (3.)-> front differential -> wheels.
The clutchpack (5.) in the transfer case is controlled electronically.
When the clutchpack is fully engaged the front and rear drive shafts gets (almost) the same torque from the engine.
BUT depending on the road conditions it can theoretically have 100/0 split f/r torque to move the car in a situation when rear wheels are on ice and only the fronts has traction. In understeer situations clutchpack disengages, front wheels loose torque and car dynamics change to oversteer (rear wheel driven).
BMW claims that xDrive is almost always engaged, but since the clutchpack always has some slip and the rear is directly connected the ratio is about 40f/60r.



If you want to see innards of a transfer case here's a link to a rebuild by kdog_x
https://f30.bimmerpost.com/forums/sh....php?t=1426356

Most of the time the xDrive is controlled nicely but sometimes I feel it holds the front engaged too long. In winter I like to enjoy drifting and "doughnuts", but sometimes when I want to spin 180 while moving it goes forward more that I expect, until the front disengages and lets you spin around.

P.S. The shaft from transmission (1.) goes through the center and is connected to the rear driveshaft (2.) and the housing (9.) of a clutchpack (5.) is always spinning. Only when the clutchpack engages the power is transferred to the gear (5A.) to drive the front driveshaft.
Wow, a very thorough and not at all a "whatever" post indeed! I've played around with XDelete on my F30 which disengages the front diff, thereby making it entirely RWD. In that app, the diff is entirely on (like OEM settings) or entirely off (RWD only). The E90 guys get a "sport" mode which is sort of in-between the two. In that setting, the front is still engaged, but less so...maybe 10-20f/80-90r? To your point, that'd be a nice middle ground between the overly conservative OEM setting and going fully balls-out RWD (which, tbh, my Stage 2 FBO car with OEM 255s in the rear just can't handle).

Anyway, I wish they'd do that with the F30, but sadly they didn't. I'm not sure why, but my guess there's a mechanical difference in the F30 that doesn't allow it like they're able to on the E90.
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