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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > x-drive vs DTC?



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      01-06-2014, 05:20 PM   #1
chong0
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x-drive vs DTC?

Hi everyone,

probably a silly question but I'm confused.

This weekend was a great weekend for donuts in the northeast. In my e91 x-drive wagon, traction control on made this very difficult. I'm assuming that the DTC was limiting my throttle and thus not giving me much power output to spin the wheels.

Shutting off DTC (3 second hold), obviously was night and day. Does shutting this off still cause power transfer to the front wheels from the rear? should it be 50-50 wheel spin from front and back axle or does the DTC being off affect this?It sure felt like a RWD car but not so sure i guess...

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      01-06-2014, 05:49 PM   #2
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This is my present understanding.

You have 3 setting available thru the "DTC" button. Full DSC (dynamic stability control) is the default, that is what comes on always when you start the car. That uses among other things, cutting throttle and individual wheel braking to control yaw and wheel spin and induces lots of plowing esp in snow. Not recommended in snow, sucks.

Next is DTC, dynamic traction control. One quick DTC button press. DTC and warning light comes on the dash. It is sort of a subset of DSC but not really. It uses individual brakes mostly to control traction and some chassis (yaw) but allows mild oversteer, and does not heavily interfere with throttle, as DSC does. You cannot get much wheel spin with DTC on. Best for snow and ice driving.

Last is both off. No traction control and no stability control. However you still have AWD and e-diff + transfer case working. So you get wheel spin both front and rear within the context of trying to keep all 4 wheels going the same rate. So no "traction control" in the sense of limiting wheel spin but maybe TQ control is a better way to think of it, still sending TQ to all the wheels via limiting the different rate of rotation using individual brakes + transfer case. Make sense?

IOW everything off on ice you should be able to spin all 4 wheels and do donuts. There is some screwy logic that lets all power go to the rears if the fronts have zero traction but the rears don't from a dead stop but I have not experienced that.

Last edited by ajsalida; 01-06-2014 at 05:59 PM.
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      01-06-2014, 06:59 PM   #3
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Quote:
Originally Posted by ajsalida View Post
This is my present understanding.

You have 3 setting available thru the "DTC" button. Full DSC (dynamic stability control) is the default, that is what comes on always when you start the car. That uses among other things, cutting throttle and individual wheel braking to control yaw and wheel spin and induces lots of plowing esp in snow. Not recommended in snow, sucks.

Next is DTC, dynamic traction control. One quick DTC button press. DTC and warning light comes on the dash. It is sort of a subset of DSC but not really. It uses individual brakes mostly to control traction and some chassis (yaw) but allows mild oversteer, and does not heavily interfere with throttle, as DSC does. You cannot get much wheel spin with DTC on. Best for snow and ice driving.

Last is both off. No traction control and no stability control. However you still have AWD and e-diff + transfer case working. So you get wheel spin both front and rear within the context of trying to keep all 4 wheels going the same rate. So no "traction control" in the sense of limiting wheel spin but maybe TQ control is a better way to think of it, still sending TQ to all the wheels via limiting the different rate of rotation using individual brakes + transfer case. Make sense?

IOW everything off on ice you should be able to spin all 4 wheels and do donuts. There is some screwy logic that lets all power go to the rears if the fronts have zero traction but the rears don't from a dead stop but I have not experienced that.
Spot on.
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      01-07-2014, 08:12 AM   #4
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I would add, despite BMW marketing efforts, it is not possible for the fronts to have 100% power, or even over 50%, in the sense the front driveshaft can never turn faster than the rear under power. And if the rear shaft is not moving the front can never move (except possibly somehow by rolling downhill with TC case disengaged and rears off the ground or locked).

The AWD system on e9x cars basically hangs the transfer case off the ordinary RWD rear driveshaft. All the TC does is variably engage or disengage clutches to the front driveshaft off the rear driveshaft. It is not a true center differential in that regard, and the best the front can get is to be locked up to the rear driveshaft's rotation rate.
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      01-07-2014, 09:24 AM   #5
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thanks very helpful and educational.
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      01-07-2014, 04:41 PM   #6
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Quote:
Originally Posted by ajsalida View Post
This is my present understanding.

You have 3 setting available thru the "DTC" button. Full DSC (dynamic stability control) is the default, that is what comes on always when you start the car. That uses among other things, cutting throttle and individual wheel braking to control yaw and wheel spin and induces lots of plowing esp in snow. Not recommended in snow, sucks.

Next is DTC, dynamic traction control. One quick DTC button press. DTC and warning light comes on the dash. It is sort of a subset of DSC but not really. It uses individual brakes mostly to control traction and some chassis (yaw) but allows mild oversteer, and does not heavily interfere with throttle, as DSC does. You cannot get much wheel spin with DTC on. Best for snow and ice driving.

Last is both off. No traction control and no stability control. However you still have AWD and e-diff + transfer case working. So you get wheel spin both front and rear within the context of trying to keep all 4 wheels going the same rate. So no "traction control" in the sense of limiting wheel spin but maybe TQ control is a better way to think of it, still sending TQ to all the wheels via limiting the different rate of rotation using individual brakes + transfer case. Make sense?

IOW everything off on ice you should be able to spin all 4 wheels and do donuts. There is some screwy logic that lets all power go to the rears if the fronts have zero traction but the rears don't from a dead stop but I have not experienced that.
That
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      01-18-2014, 03:30 PM   #7
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word!
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      01-20-2014, 04:17 PM   #8
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