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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > XDrive a bad system?



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      08-20-2013, 12:36 PM   #1
sy2767
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XDrive a bad system?

I have noticed that the consensus seems to be that BMW's system is under par and almost frowned upon compared to other manufactures AWD systems, what makes it an inferior design?
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      08-20-2013, 12:51 PM   #2
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There are comparison tests all over youtube. Type in something like "quattro xdrive 4matic"
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      08-20-2013, 01:25 PM   #3
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Quote:
Originally Posted by Amini77 View Post
There are comparison tests all over youtube. Type in something like "quattro xdrive 4matic"
I've watched them all before, i'm not asking for a comparison between it and other systems, i'm asking why its not considered as good as others.
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      08-20-2013, 02:10 PM   #4
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Quote:
Originally Posted by sy2767 View Post
I've watched them all before, i'm not asking for a comparison between it and other systems, i'm asking why its not considered as good as others.
Then I don't quite understand where you're seeing that. They're all pretty equal. Unless you're looking at the comments then its just BMW vs Audi guys. Of course the Audi guys have more influence on the web because they're enthusiasts all have quattro and the xdrive guys don't really care because majority of the BMW enthusiasts have RWD so why waste time trying to make people believe xdrive is better. If I sound crazy sorry lol I got no sleep last night
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      08-20-2013, 02:33 PM   #5
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I agree, I'm not sure where you're seeing/hearing that. Coming from an Audi with their Torsen mechanical system I think it's better than BMW's, but not by much. Based on what I've driven/read Subie and Audi are 1a and 1b, then BMW comes in next with Lexus, Merc and Audi's Haldex following.
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      08-20-2013, 03:10 PM   #6
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Quote:
Originally Posted by zipstic View Post
I agree, I'm not sure where you're seeing/hearing that. Coming from an Audi with their Torsen mechanical system I think it's better than BMW's, but not by much. Based on what I've driven/read Subie and Audi are 1a and 1b, then BMW comes in next with Lexus, Merc and Audi's Haldex following.
I have seen it in magazine reviews and online comparisons where (as you just stated yourself) Subie, and Audi are better, im just asking what makes them better? Trying to understand the system BMW uses.
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      08-20-2013, 03:21 PM   #7
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Well one thing that would make it better is a true LSD rear and a true center diff that you could lock or shut off. It is a good basic system but it relies a lot on the brakes to send traction across axles on an open mechanical diff.

the transfer case on xdrive is just a set of clutches hanging off a conventional driveshaft between tranny output to the rear diff. You cannot disengage the rears in other words, it is not a diff, you can only engage the front driveshaft from 0 to full lock with the rear driveshaft. More sophisticated systems can send infinitely variable power/tq either front or rear, 0-100%.

Again none of this is bad, it works well, just not very high tech. Also nothing, zero, under driver control which to me is worse.

Last edited by ajsalida; 08-20-2013 at 03:27 PM.
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      08-20-2013, 03:38 PM   #8
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Quote:
Originally Posted by sy2767 View Post
I have noticed that the consensus seems to be that BMW's system is under par and almost frowned upon compared to other manufactures AWD systems, what makes it an inferior design?
As mentioned by AJ, mechanically locking center and rear diffs. The BMW system is quite simple, but it's actually quite effective. The center diff is variable in torque split front rear, driven by the DSC and other software. The rear diff is an open diff (as is the front) and uses Automated Differential Braking (ADB) to lock/slow spinning wheels, which transfers torque to the opposite side (which presumably has better traction since it's not spinning.)

However, other systems which use mechanical means to lock the left/right (and even front/rear axles) to a greater or lesser extent have advantages in some situations. For instance, unless you turn on DTC, a BMW can get bogged down due to 1) traction control dialing down power/throttle, and 2) stopping the spinning wheel may not actually cause the car to move if the other wheel also has little/no traction.

In reality, none of this matters a whole lot, as most people never approach the limits of available traction, and we're only talking about the last 5% or so of performance. Frankly, if you're at that limit, you should be home and the BMW should be in the garage.
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      08-20-2013, 03:46 PM   #9
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Whats the big deal who cares which is better. It does the job. My RWD with snow tires out performs many X drive systems w/ all seasons. I've proven it every winter.
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      08-20-2013, 03:57 PM   #10
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I don't know what makes it inferior. I also don't actually know if BMWs system is 4WD or AWD. I only know that if you want four wheel/all wheel drive and you are committed to owning a BMW, dwelling about it will only miff you.

Here is an excellent discourse on the basic engineering, functionality and pros and cons of each of the types of drive systems.
http://gearpatrol.com/2013/03/29/fou...-need-to-know/ . It seems that "the best", as it nearly always is, depends on conducting one's own cost/benefit assessment more so than there being an absolute "best."

All the best.
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      08-20-2013, 04:40 PM   #11
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Quote:
Originally Posted by ihsanshaik View Post
Whats the big deal who cares which is better. It does the job. My RWD with snow tires out performs many X drive systems w/ all seasons. I've proven it every winter.
Yeah I can see this on plowed flat roads. The nice thing about AWD in winter is you just don't have to think so much. I have a RWD car I drive in winter, under the right conditons, even up to the ski area in good weather it requires 100% focus. AWD not so much, plus in (much) worse conditions it is not such a white knuckle experience. Extra safety margin and overall traction + lateral grip is so far above RWD it isn't even close.

For the truly deep and scary stuff I have a 4wd tacoma.

I live @ 8k ft and winter is spent between there and 12k ft. 40-50 ft year of snow up top.
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      08-20-2013, 09:27 PM   #12
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Originally Posted by ihsanshaik
Whats the big deal who cares which is better. It does the job. My RWD with snow tires out performs many X drive systems w/ all seasons. I've proven it every winter.
That's why you get an xi/xdrive with snow tires. No contest
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      08-20-2013, 10:02 PM   #13
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Quote:
Originally Posted by floydarogers View Post
As mentioned by AJ, mechanically locking center and rear diffs. The BMW system is quite simple, but it's actually quite effective. The center diff is variable in torque split front rear, driven by the DSC and other software. The rear diff is an open diff (as is the front) and uses Automated Differential Braking (ADB) to lock/slow spinning wheels, which transfers torque to the opposite side (which presumably has better traction since it's not spinning.)

However, other systems which use mechanical means to lock the left/right (and even front/rear axles) to a greater or lesser extent have advantages in some situations. For instance, unless you turn on DTC, a BMW can get bogged down due to 1) traction control dialing down power/throttle, and 2) stopping the spinning wheel may not actually cause the car to move if the other wheel also has little/no traction.

In reality, none of this matters a whole lot, as most people never approach the limits of available traction, and we're only talking about the last 5% or so of performance. Frankly, if you're at that limit, you should be home and the BMW should be in the garage.
Thank you!
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      08-21-2013, 09:07 AM   #14
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Quote:
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That's why you get an xi/xdrive with snow tires. No contest
+11111111

i hate when RWD people who drive in minimal snow claim their cars handle better than AWD with all seasons. Even those with AWD put snows on their cars.
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      08-24-2013, 07:33 PM   #15
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+11111111

i hate when RWD people who drive in minimal snow claim their cars handle better than AWD with all seasons. Even those with AWD put snows on their cars.
All I can say is My E90 does its job in the winter.
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      08-28-2013, 10:22 AM   #16
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My 335xi dominates inclement weather, particularly with DTC on. In the snow, with DTC on, I find the car to be very similar to the VC center diff of my old suby, which I thought was a very good system.

Would I rather LSDs? Yea. But functionally, I've no complaints.
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