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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > Your experience with DTC/DSC in winter conditions.



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      09-17-2016, 11:43 AM   #1
lhuynh336
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Your experience with DTC/DSC in winter conditions.

I just wanted to hear people's feedback about their xi's in the winter time. I often drive myself up the mountains in the winter time to go snowboard in the 335xi. I do turn on DTC for the road conditions and feel very confident in the car. I love the fact that DTC allows the tail to come out while keeping you in line. This past winter I did have the opportunity with a empty parking lot to myself testing DSC off. It was still pretty easy to control the car but I felt much more safer with DTC.
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      09-17-2016, 12:59 PM   #2
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I like dtc for slushy/or snow condition it allows for bit of fun before the nanny puts a kibosh on it.
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      09-17-2016, 06:51 PM   #3
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I constantly have it all turned off when it snows. I want control of my car...not the ecu trying to do what it thinks is best. These cars are tanks in the snow. I went out during last years blizzard and had no trouble as long as everything was turned off. But, it really all depends on your abilities as a driver and how properly prepped your car is for winter. If you arent super confident to handle yourself in sketchy situations then leave that stuff turned on.
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      09-17-2016, 07:43 PM   #4
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Mine is always off and no XI here first winter was scary but know I can handle it
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      12-13-2016, 06:06 PM   #5
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I have a 328xi wagon that I just acquired and I'm getting used to the car, the x-drive mechanical system, and the electronic systems.
As this is meant to be a ski car my very first aftermarket purchase was a square set of performance winter tires (Sottozeros) and some rims. It snowed in the lowlands and I took it out in a parking lot for test donuts , and then last weekend I took it to the ski areas over some nasty roads and then for grins I tried to drive it up and down some steep unplowed roads.

My understanding of the mechanical is that just behind the transmission is a transfer case that has an electronically-controlled clutch pack and that the front and rear differentials are open.

My visceral understanding of electronics is normal = boring and pointless
DTC = a little tail happy and better for the real nasty stuff like the unplowed hill but still will keep you in control.
DSC off = donut time, intentional or not.

My questions are: I assume that the front and rear both have "e-lsd" wherein the side to side slip on both axles is controlled by schmancy-pants individual braking.
1) Is this still on in DTC?
2) Is it different in DTC?
3) Is this still on in full DSC-off mode?

And then relating to the central clutch pack:
4) Does DTC effect clutch engagement, aka, does it "4 wheel lock" like a pickup truck transfer case in DTC? I think some Jeep AWD systems work like this.
5) Any central clutch changes in full DSC-off mode?

Thanks for any answers to these technical questions! Needless to say, the legalese filled owner's manual was of little help!
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      12-13-2016, 07:31 PM   #6
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There was another recent thread where this is discussed.

1) the e-diff, called Automated Differential Braking (ADB) is always enabled; turning off DSC does not turn it off.
2) The clutch pack defaults to the normal 40:60 split (I believe) when DSC is off.
3) DTC just expands the amount of wheelspin allowed by the system, and does not affect the clutches per se.
4) The transfer case - it's not a differential - doesn't lock (other than send 100% to the rear). Although the documentation says that 100% can be sent to the front, that is not actually the case, as the rear driveshaft is always driven.
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      12-13-2016, 07:44 PM   #7
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Hmm I didn't find it, thank you very much for your direct and informative answers though! My curiousity continues:

1) No further questions, your honor.
2) So the clutches vary torque in normal and DTC mode but are set at 40:60 split in DSC-off?
3) Is DTC just the same as a performance driving stability mode and thus I should leave it on all the time?
4) I agree that's marketing BS unless the it can fully release the rear driveshaft and clutch only to the front.
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      12-13-2016, 09:03 PM   #8
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Quote:
Originally Posted by Rocklicker View Post
Hmm I didn't find it, thank you very much for your direct and informative answers though! My curiousity continues:

1) No further questions, your honor.
2) So the clutches vary torque in normal and DTC mode but are set at 40:60 split in DSC-off?
3) Is DTC just the same as a performance driving stability mode and thus I should leave it on all the time?
4) I agree that's marketing BS unless the it can fully release the rear driveshaft and clutch only to the front.
Again, I'm speculating a bit that it goes to 40:60 with DSC off. That's for sure the default in normal driving with no f:r slippage detected.

I only use DTC on snow where I know I need to use a bit more power to climb a hill. No worries about leaving it on all the time (but it's annoying to hit it every time you start.)
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      12-13-2016, 10:40 PM   #9
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Thanks!
Testing:



Last edited by Rocklicker; 12-14-2016 at 05:08 PM. Reason: fixed hyperlinks
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      12-14-2016, 04:28 PM   #10
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I've been doing great in my past winters with the 335xi on a set of continental DWS's. I now have Michelin Pilot super sports and I'm a bit afraid to drive with those tires in the snow.
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      12-14-2016, 05:34 PM   #11
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Do not drive on summer performance tires like Super Sports in the snow. AWD will make no difference and the chance of disaster is very high. I have decades of experience driving in snow like you see in the photos above and the couple times I've done it on summer performance tires were truly ass-clenching experiences.
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      12-14-2016, 06:26 PM   #12
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Couple of points.

1) e-diff is off when DSC is full off on mid-08 model year and earlier cars. Later cars it is on always. It can be coded out however.

2) DTC is in some sense a subset of DSC. DSC cuts throttle to achieve certain stability control parameters, DTC does not. DTC will limit wheel spin and portion out traction (2 different things) using individual brakes and transfer case. I run with DTC on in winter, car throttle will bog heavily with DSC full on in some situations, in DTC nope. Plus DTC is more fun. DSC full off is fun too but not so much where I live (remote high rockies).

3) The AWD system is always on, as far as the transfer case and (maybe) brakes modulating TQ to wheels. There is just no wheel spin control with DSC full off. Eg you can spin all 4 wheels with DSC full off in right conditions, you cannot do that in DTC mode. In a mid-08 and later car you may still have F&R e-diff stuff bundled with AWD still working in an intelligent way. Normal conditions TQ split is 40/60 F/R but that will change dynamically based on conditons. The most that can be sent to the front axles is 50% with TC case fully locked up, as the rear driveshaft cannot be disconnected with clutches, it is a hard line straight thru the TC. This will happen when for example, rears are on ice and fronts have some traction. The rears will turn in lock step with the fronts. 100% will go to the rears if fronts have no traction an rear does. Here the fronts will not spin if the TC is disengaged. Over a certain (high) speed TC is open and front receives no TQ anyway, as well as very low speeds turning like in a parking lot.

Last edited by ajsalida; 12-14-2016 at 06:32 PM.
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      12-14-2016, 06:53 PM   #13
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Thank you AJSalida, a great explanation!
Arghh I bought another model year split car?! I hate those! How do I tell which side of the split my 2008 is on? While doing important dynamic low speed vehicle testing (aka donuts in a snowy parking lot) I think all 4 were spinning with full DSC-off, but I can't be certain. The tire tracks and the feel of the car suggested it, but I didn't have an outside observer.
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      12-14-2016, 07:20 PM   #14
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Quote:
Originally Posted by Rocklicker View Post
Thank you AJSalida, a great explanation!
Arghh I bought another model year split car?! I hate those! How do I tell which side of the split my 2008 is on? While doing important dynamic low speed vehicle testing (aka donuts in a snowy parking lot) I think all 4 were spinning with full DSC-off, but I can't be certain. The tire tracks and the feel of the car suggested it, but I didn't have an outside observer.
I think it happened with the switch over from MSD80 to 81 but not sure. Compounding this uncertainty is it is NOT clear if e-diff on Xdrive received the same treatment as e-diff on RWD cars before/after. Eg it maybe possible that e-diff on AWD can never be turned off regardless of pre/post mid-08. I don't know. In some sense some e-diff function is integral with AWD in a way it is not with RWD.

It may be that on Xdrive cars e-diff by necessity must be available for the TC & AWD system to function properly, even with DSC full off. Imagine a scenario where only one front wheel has traction, other 3 on ice. TC engaged, sends full TQ to front axle. 3 other wheels spin and wheel with traction just sits there not turning. The only way you get moving is if e-diff clamps n the front wheel that is spinning, sending TQ to the other front wheel with traction.

This is what happens in a RWD car when rear e-diff is off and only one wheel has traction, wheel with no traction just spins and you just sit there. I suppose this hypothesis would be easy to test on AWD if one were so inclined.

WhatEVer. I think e-diff is a good thing, not as good as a true rear LSD but good enough. And without it in front you'd be screwed regardless.

Last edited by ajsalida; 12-14-2016 at 07:38 PM.
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      12-14-2016, 07:42 PM   #15
ajsalida
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This is worth reading if you haven't

http://www.bmw.com/com/en/insights/t...action_control
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      12-14-2016, 09:20 PM   #16
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I'm glad BMW gives the option of DTC mode kind of between DSC and off. I routinely push the button to switch every time I start the car. I wish it could be set as default.

You can't call a car a "driving machine" that cuts power to the engine or selectively brakes wheels when the driver is trying to do (and expecting) what he wants the car to do. I find it annoying how interventionist DSC is, but I can certainly see how it adds a lot of safety for the people who own these cars as appliances.

DTC, OTOH, still provides a bit of a safety net from things getting too out of hand while allowing some driving fun. If I could only choose between DSC and off, it would always be off.
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      12-14-2016, 10:08 PM   #17
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Is that codeable?
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      12-15-2016, 05:14 PM   #18
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From my admittedly cursory checking it does not appear so.
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      12-15-2016, 05:43 PM   #19
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I have the 2011 328xi sports wagon. How do I switch between DTC & DSC and how do I turn them on and off? Sorry... CA doesn't see much rain or snow.
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      12-15-2016, 05:47 PM   #20
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1. You cannot get to DSC off from DTC. You have to turn DTC back off, then press and hold the DTC button for 6 seconds.

2. Verify with donuts in a wet parking lot.
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      12-16-2016, 12:11 AM   #21
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My town just got a ton of snow and I decided to test out the car with DTC and DSC turned off. I'm on DWS-06's all around, and with the DTC/DSC off, the car would just spin out from a dead stop, and would get really squirrely in straight lines. With them enabled, the car can just launch off the line in packed/fresh snow, and tire slip is predicatble. I'm able to get up all the steep hills and back down as well as around corners.

Can't believe how good the DWS-06 is in the snow either, it's quite unbelievable!
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      12-16-2016, 03:50 PM   #22
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Quote:
Originally Posted by BurtMacklin View Post
My town just got a ton of snow and I decided to test out the car with DTC and DSC turned off. I'm on DWS-06's all around, and with the DTC/DSC off, the car would just spin out from a dead stop, and would get really squirrely in straight lines. With them enabled, the car can just launch off the line in packed/fresh snow, and tire slip is predicatble. I'm able to get up all the steep hills and back down as well as around corners.

Can't believe how good the DWS-06 is in the snow either, it's quite unbelievable!
Just imagine if you had true dedicated winter or snow tires
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