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      05-21-2015, 06:31 PM   #1
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Accurate description of xDrive?

http://www.awdwiki.com/en/xdrive/ :

"Proactive automatic all wheel drive system. The rear wheels are powered at all times. Torque can be transferred to the front wheels via electronically controlled multi plate clutch that is located in the transfer case. XDrive does not have a center differential. Most of the time, the clutch is partially locked and power is transferred to both axles in proportion 40/60 front to rear. The power distribution can be altered to continuously variable levels (from 50/50 to 0/100). For example, when driving at high speed, or when parking, the clutch is disengaged and all power goes to the rear wheels.

XDrive is linked to DSC (Dynamic Stability Control) - when the vehicle understeers, the clutch is disengaged thus transferring more torque to the rear wheels (10/90 torque split). When oversteering is detected, the clutch locks fully transferring more power to the front wheels (50/50 torque split).

DSC (Dynamic Stability Control) also brakes wheels individually to regain traction and to help cornering. XDrive intervenes before the car becomes unstable and is unnoticeable by the driver."


Do you long-time Bimmer experts agree with this summary? (I'm trying to better understand how my F32 coupe operates.) Thanks, in advance, for any wisdom offered.
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      05-22-2015, 08:03 AM   #2
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Sounds about right.
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      05-22-2015, 09:29 AM   #3
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Yes it's an accurate description. X drive is not the best in the market especially for winter driving but better than rear wheel drive that's for sure. Subaru symmetrical all wheel drive is the best system in my opinion.
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      05-22-2015, 09:32 AM   #4
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Quote:
Originally Posted by Ali Shiralian View Post
Yes it's an accurate description. X drive is not the best in the market especially for winter driving but better than rear wheel drive that's for sure. Subaru symmetrical all wheel drive is the best system in my opinion.
It's decent, there are better systems that when coupled with 50/50 weight bias are even better. Experienced that this winter here in Alaska. Make no mistake, the subaru system is worlds above others and amazingly reliable considering how many moving parts there are compared to other non-awd cars.
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      05-22-2015, 10:30 AM   #5
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Does anyone know if Acura AWD better then Lexus AWD ?
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      05-22-2015, 10:34 AM   #6
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Yes, the X-Drive system (and sadly the Haldex in my S3) work on what's called "open differentials". Basically, if you lifted the cars on a lift with all the wheels off the ground one wheel on each side would turn opposite from the other. On the road the resistance causes the wheels to drive forward together.

In reality this is a two wheel drive system, one wheel on each axle has power. That's a simplistic representation, but an easy way to think about it.

To make the system more capable they use what is called EDL (Electronic Differential Lock), sounds fancy, but that's what it means by using the brakes controlled by the DSC. When a wheel starts to slip that would make the OTHER wheel lose traction as well, since now there is no resistance. By braking the slipping wheel it provides resistance to the other side to keep forward traction.

It works. It's not great. In similar conditions in my neighborhood my big Q5 TDI handled like it was dry, even goosing the 426ft/lbs of torque didn't upset it in the snow. While my low and sleek F31 got loose with DSC lights flashing like the end of the world the first time I goosed it on the snow covered uphill, off camber right turn leaving my street.

What I disagree with is the "proactive" part. By definition the system is REACTIVE. A wheel has to slip before the system takes effect. I guess what they mean is the stability sensors can "see" understeer/oversteer coming and prepare for it/reduce it, but I just find that part misleading to a degree.

More effective systems like Quattro have true mechanical differentials where both wheels have power no matter what, with clutch packs to control power to each wheel. Power reduction (basically) at the wheel slipping is used first before resorting to braking the wheel under traction/stability control systems.

In a slipping condition remember the brakes job is to STOP the wheel. A wheel that is slipping because it is spinning to fast can quickly become a wheel that is slipping because it is stopped completely. This can lead to the system fighting itself if the driver doesn't react themselves and dump power at least slightly.


The Subbie system is certainly the most complicated out there LOL but very effective I agree. Do they have the ability to send all the power to either axle or is it always split still?
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      05-22-2015, 11:06 AM   #7
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Quote:
Originally Posted by Thumper333 View Post
Yes, the X-Drive system (and sadly the Haldex in my S3) work on what's called "open differentials". Basically, if you lifted the cars on a lift with all the wheels off the ground one wheel on each side would turn opposite from the other. On the road the resistance causes the wheels to drive forward together.

In reality this is a two wheel drive system, one wheel on each axle has power. That's a simplistic representation, but an easy way to think about it.

To make the system more capable they use what is called EDL (Electronic Differential Lock), sounds fancy, but that's what it means by using the brakes controlled by the DSC. When a wheel starts to slip that would make the OTHER wheel lose traction as well, since now there is no resistance. By braking the slipping wheel it provides resistance to the other side to keep forward traction.

It works. It's not great. In similar conditions in my neighborhood my big Q5 TDI handled like it was dry, even goosing the 426ft/lbs of torque didn't upset it in the snow. While my low and sleek F31 got loose with DSC lights flashing like the end of the world the first time I goosed it on the snow covered uphill, off camber right turn leaving my street.

What I disagree with is the "proactive" part. By definition the system is REACTIVE. A wheel has to slip before the system takes effect. I guess what they mean is the stability sensors can "see" understeer/oversteer coming and prepare for it/reduce it, but I just find that part misleading to a degree.

More effective systems like Quattro have true mechanical differentials where both wheels have power no matter what, with clutch packs to control power to each wheel. Power reduction (basically) at the wheel slipping is used first before resorting to braking the wheel under traction/stability control systems.

In a slipping condition remember the brakes job is to STOP the wheel. A wheel that is slipping because it is spinning to fast can quickly become a wheel that is slipping because it is stopped completely. This can lead to the system fighting itself if the driver doesn't react themselves and dump power at least slightly.


The Subbie system is certainly the most complicated out there LOL but very effective I agree. Do they have the ability to send all the power to either axle or is it always split still?
Not sure about the STi, but my friend said his WRX is always locked at 50/50.
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      05-22-2015, 12:41 PM   #8
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Thanks, all --- exactly the types of knowledgeable responses I was seeking!

(I lived many years in Alaska --- where Subaru and 4WD pickups ruled the winter roads. Here in NorCal, my xDrive F32 and my Tundra are perfect for my winter needs and wants.)

Thanks again.
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      05-22-2015, 01:58 PM   #9
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Quote:
Originally Posted by crono06
Quote:
Originally Posted by Thumper333 View Post
Yes, the X-Drive system (and sadly the Haldex in my S3) work on what's called "open differentials". Basically, if you lifted the cars on a lift with all the wheels off the ground one wheel on each side would turn opposite from the other. On the road the resistance causes the wheels to drive forward together.

In reality this is a two wheel drive system, one wheel on each axle has power. That's a simplistic representation, but an easy way to think about it.

To make the system more capable they use what is called EDL (Electronic Differential Lock), sounds fancy, but that's what it means by using the brakes controlled by the DSC. When a wheel starts to slip that would make the OTHER wheel lose traction as well, since now there is no resistance. By braking the slipping wheel it provides resistance to the other side to keep forward traction.

It works. It's not great. In similar conditions in my neighborhood my big Q5 TDI handled like it was dry, even goosing the 426ft/lbs of torque didn't upset it in the snow. While my low and sleek F31 got loose with DSC lights flashing like the end of the world the first time I goosed it on the snow covered uphill, off camber right turn leaving my street.

What I disagree with is the "proactive" part. By definition the system is REACTIVE. A wheel has to slip before the system takes effect. I guess what they mean is the stability sensors can "see" understeer/oversteer coming and prepare for it/reduce it, but I just find that part misleading to a degree.

More effective systems like Quattro have true mechanical differentials where both wheels have power no matter what, with clutch packs to control power to each wheel. Power reduction (basically) at the wheel slipping is used first before resorting to braking the wheel under traction/stability control systems.

In a slipping condition remember the brakes job is to STOP the wheel. A wheel that is slipping because it is spinning to fast can quickly become a wheel that is slipping because it is stopped completely. This can lead to the system fighting itself if the driver doesn't react themselves and dump power at least slightly.


The Subbie system is certainly the most complicated out there LOL but very effective I agree. Do they have the ability to send all the power to either axle or is it always split still?
Not sure about the STi, but my friend said his WRX is always locked at 50/50.
This is true of the older Scoobies but later models had a variable LSD that could be controlled by the driver
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      05-22-2015, 02:02 PM   #10
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Quote:
Originally Posted by Thumper333
Yes, the X-Drive system (and sadly the Haldex in my S3) work on what's called "open differentials". Basically, if you lifted the cars on a lift with all the wheels off the ground one wheel on each side would turn opposite from the other. On the road the resistance causes the wheels to drive forward together.

In reality this is a two wheel drive system, one wheel on each axle has power. That's a simplistic representation, but an easy way to think about it.

To make the system more capable they use what is called EDL (Electronic Differential Lock), sounds fancy, but that's what it means by using the brakes controlled by the DSC. When a wheel starts to slip that would make the OTHER wheel lose traction as well, since now there is no resistance. By braking the slipping wheel it provides resistance to the other side to keep forward traction.

It works. It's not great. In similar conditions in my neighborhood my big Q5 TDI handled like it was dry, even goosing the 426ft/lbs of torque didn't upset it in the snow. While my low and sleek F31 got loose with DSC lights flashing like the end of the world the first time I goosed it on the snow covered uphill, off camber right turn leaving my street.

What I disagree with is the "proactive" part. By definition the system is REACTIVE. A wheel has to slip before the system takes effect. I guess what they mean is the stability sensors can "see" understeer/oversteer coming and prepare for it/reduce it, but I just find that part misleading to a degree.

More effective systems like Quattro have true mechanical differentials where both wheels have power no matter what, with clutch packs to control power to each wheel. Power reduction (basically) at the wheel slipping is used first before resorting to braking the wheel under traction/stability control systems.

In a slipping condition remember the brakes job is to STOP the wheel. A wheel that is slipping because it is spinning to fast can quickly become a wheel that is slipping because it is stopped completely. This can lead to the system fighting itself if the driver doesn't react themselves and dump power at least slightly.


The Subbie system is certainly the most complicated out there LOL but very effective I agree. Do they have the ability to send all the power to either axle or is it always split still?
I had recent experience of the Haldex system on a Saab AWD Turbo X - I was not a fan to be honest....especially when compared to my old Impreza Turbo.

I now have an XDrive 435d and find this system much less 'choppy' than the Haldex which sometimes seemed to throw the power too quickly from front to back.
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      05-22-2015, 02:10 PM   #11
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Quote:
Originally Posted by Lcfcno1fan View Post
This is true of the older Scoobies but later models had a variable LSD that could be controlled by the driver
That's what I thought too, but I asked and he said he doesn't have it. I've been in it as well and there was no controller. His is a 2013 or 2014 (previous gen). He said only the STi got that =S
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      05-22-2015, 02:13 PM   #12
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Quote:
Originally Posted by crono06
Quote:
Originally Posted by Lcfcno1fan View Post
This is true of the older Scoobies but later models had a variable LSD that could be controlled by the driver
That's what I thought too, but I asked and he said he doesn't have it. I've been in it as well and there was no controller. His is a 2013 or 2014 (previous gen). He said only the STi got that =S
Shame as the Subaru chassis is one of the most 'sorted' out there - but they have really lost their way over the last few years :-(
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      05-22-2015, 02:19 PM   #13
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Quote:
Originally Posted by Lcfcno1fan View Post
This is true of the older Scoobies but later models had a variable LSD that could be controlled by the driver
But aren't they still limited from reaching full 100% to either axle? I think 50/50 is the default and then depending on the setting the driver selects and the conditions it can go up to 80/20 max? Not sure.


Quote:
Originally Posted by Lcfcno1fan View Post
I had recent experience of the Haldex system on a Saab AWD Turbo X - I was not a fan to be honest....especially when compared to my old Impreza Turbo.

I now have an XDrive 435d and find this system much less 'choppy' than the Haldex which sometimes seemed to throw the power too quickly from front to back.
I am lucky I guess to be able to experience all these things (except the Subbies, almost got a WRX once, but didn't LOL) I have a real Quattro, a Haldex, and an X-Drive.

I am betting the issue you had with the Saab (which was the 2nd generation I bet, we're on 5th Gen now) is that Haldex leans toward FWD bias, X-drive is a RWD biased system. That Saab defaulted to something like 90% power to the front wheels I think.
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      05-22-2015, 02:24 PM   #14
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Quote:
Originally Posted by Thumper333
Quote:
Originally Posted by Lcfcno1fan View Post
This is true of the older Scoobies but later models had a variable LSD that could be controlled by the driver
But aren't they still limited from reaching full 100% to either axle? I think 50/50 is the default and then depending on the setting the driver selects and the conditions it can go up to 80/20 max? Not sure.


Quote:
Originally Posted by Lcfcno1fan View Post
I had recent experience of the Haldex system on a Saab AWD Turbo X - I was not a fan to be honest....especially when compared to my old Impreza Turbo.

I now have an XDrive 435d and find this system much less 'choppy' than the Haldex which sometimes seemed to throw the power too quickly from front to back.
I am lucky I guess to be able to experience all these things (except the Subbies, almost got a WRX once, but didn't LOL) I have a real Quattro, a Haldex, and an X-Drive.

I am betting the issue you had with the Saab (which was the 2nd generation I bet, we're on 5th Gen now) is that Haldex leans toward FWD bias, X-drive is a RWD biased system. That Saab defaulted to something like 90% power to the front wheels I think.
I think you are right and it was bloody awful at times :-(
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