[VIDEO] xDrive, how it works?

[The long haul]

I for one would like to see cold hard sales figures to support that BMW Xdrive outsells Quattro. I for one don't buy that for a second.

[DJKhan85]

Originally Posted by PackPride85

I didn't listen to the audio in the 2nd video, but these tests kinds of tests are completely bogus. Audi's system uses a Torsen (aka torque sensing) center diff. It's a purely mechanical set up that will multiply existing torque on one axle by some factor and transfer it to the other axle. The key is that there has to be some small amount of torque present or else 0 x 0 = 0. Despite that, its still a great system and is easy/cheap to implement. The transverse mounted audi's use haldex which is an xdrive type clutch setup.

Xdrive uses electronically activated clutches to engage the front axle (no true center diff), thus being able to transfer 100% of the torque to either axle even in 100% slip conditions (usually maintains a partial lock to maintain a rear bias of 60/40 I believe). Is it better than a torsen system? In the extremely unlikely event (and by that I mean impossible) that you have ZERO traction on BOTH wheels of an axle, then yes xdrive is superior. The fact that it uses sensors means it should be able to "detect" slippage before lost of traction (using steering angle, throttle, etc...)as well is another advantage.

What's really more important is the traction between wheels on each axle. Most of these cars with open diffs and traction control will brake the spinning wheel to transfer torque across the axle. My guess during this test was that they disabled that for the Audi and left it enabled on the BMW.

If you want a true performance AWD system look at a WRX STI. An adjustable viscous coupling center diff, which while slower to react can transmit torque in complete no slip situations, and torsen LSD diffs on the front and back (pre 2011). That setup blows the doors off xdrive and quattro.

Honestly, I think actual awd performance for quattro vs xdrive has more to do with how the DSC is programmed for same axle traction and tire size/type instead of how the power gets to each axle. If BMW wanted to throw an mechanical LSD or two along with Xdrive it probably would make a formidable performance AWD system.

I normally hate browsing these AWD threads since most people have no idea how any of the AWD systems actually work. Instead they just believe the marketing hype that gets played by the individual companies. I am glad that your post proves people still go out there and do hard research on AWD systems.

Most of the AWD systems rely heavily on computer intervention (except for the aforementioned STI, which is different than the other subaru AWD systems). The computer will either cut power, open/close a clutch that controls power to the rear wheels (as does xdrive, at least the versions I read about in the 2008 models) or brake wheel(s) to get the power where the computer determines it should be sent.

From what I recall the xdrive system has the front axle connected to the output of the transmission via a chain system that cannot be decoupled. There is then a clutch pack that power must go through from the transmission to get to the rear wheels. The only way I can see the claim "100% of power to either axle" being true is if you take into account the brakes on one axle being applied, momentarily, to stop the wheels on that axle. Then the power has no where to go but to the other axle.

I wonder if the xdrive system is different across all BMW models or if it's just computer programming.

[FilipMPower]

Originally Posted by mkoesel

It could, but the general public is afraid of understeer. Well, that may not be totally fair - they are perhaps just not accustomed to it. You see, since most passenger cars are FWD, people moving up to a luxury car with RWD may not be familiar with it's driving dynamics. Therefore, to make luxury cars more friendly to such people - who represent a large number of buyers, many of whom would not even be interested in buying the car if it were RWD - AWD cars are often purposely made to handle more like FWD cars (or at the very least, are made not to oversteer like a RWD car would).

I understand. Believe it or not, I never drove a FWD or AWD car. Every car I had was RWD. So I never really experienced understeer except for the standard, small understeer when exiting a corner with throttle. I don't know, would you say it is terrible, or annoying, the understeer in xDrive, if there is any?

[PackPride85]

I can almost guarantee for the roller video they disabled the DSC system on the audi. If it was enabled it would have engaged the brakes on the spinning wheel allowing the open diff to transfer torque to the other wheel on the ground. It's a BMW video so wouldn't surprise me.

As for the "real life" test vid in the snow/ice above there are other factors that come into play as well. Tire type, tire pressure, gearing, and driver ability all are factors.

I used to see plenty of soccer mom's in their bmw/audi SUVs slide down hills bc they just flat out didn't know how to drive in the snow. Meanwhile I'd be passing them up hill in an 88 sentra starting in 2nd gear with shitty goodyear snow tires.

I wouldn't base a car purchase on one marketing awd hype over the other. If you suck at driving no awd system will save you.

[PackPride85]

Originally Posted by DJKhan85

I normally hate browsing these AWD threads since most people have no idea how any of the AWD systems actually work. Instead they just believe the marketing hype that gets played by the individual companies. I am glad that your post proves people still go out there and do hard research on AWD systems.

Most of the AWD systems rely heavily on computer intervention (except for the aforementioned STI, which is different than the other subaru AWD systems). The computer will either cut power, open/close a clutch that controls power to the rear wheels (as does xdrive, at least the versions I read about in the 2008 models) or brake wheel(s) to get the power where the computer determines it should be sent.

From what I recall the xdrive system has the front axle connected to the output of the transmission via a chain system that cannot be decoupled. There is then a clutch pack that power must go through from the transmission to get to the rear wheels. The only way I can see the claim "100% of power to either axle" being true is if you take into account the brakes on one axle being applied, momentarily, to stop the wheels on that axle. Then the power has no where to go but to the other axle.

I wonder if the xdrive system is different across all BMW models or if it's just computer programming.

It's not a permanent torque split anymore. I believe its a wet clutch variable system so you can literally get 100% to either axle.

Performance wise, it all relies on how they tune the system and its sensors.

[mkoesel]

Originally Posted by The long haul

I for one would like to see cold hard sales figures to support that BMW Xdrive outsells Quattro. I for one don't buy that for a second.

Well, I don't know where that statistic originates, but it's well known that BMW comfortably outsells Audi in total sales both here in the US and worldwide. I believe they beat Audi in the US in every single segment in which the two compete, including by huge margin in the entry level luxury sedan segment (3 Series and A4/S4).

Keep in mind, while in the US there are only a couple models where Quattro isn't standard (one of which is the A4, by the way), worldwide, all of their passenger cars and, I believe, some of their SUVs are available without Quattro (in which case they are FWD).

So, when you take the two above together, it is not hard to see how BMW could theoretically be selling more AWD vehicles than Audi. It certainly doesn't confirm it, but I have no trouble at all believing it could be the case.

[Hobbe74]

Originally Posted by m_alnimah

To be Honest, xDrive is waaaay better than both 4Matic and Quattro as seen in the second video.... And i assume that VW's 4Motion is just like Quattro...

VW 4Motion is from Haldex, same as Volvo uses. FWD with help from rear if no or bad traction on front axle = so-so.
Audi uses more then one system, depending on model, but name them all Quattro.

[ORIGIN M.]

Originally Posted by DJKhan85

I normally hate browsing these AWD threads since most people have no idea how any of the AWD systems actually work. Instead they just believe the marketing hype that gets played by the individual companies. I am glad that your post proves people still go out there and do hard research on AWD systems.

Most of the AWD systems rely heavily on computer intervention (except for the aforementioned STI, which is different than the other subaru AWD systems). The computer will either cut power, open/close a clutch that controls power to the rear wheels (as does xdrive, at least the versions I read about in the 2008 models) or brake wheel(s) to get the power where the computer determines it should be sent.

From what I recall the xdrive system has the front axle connected to the output of the transmission via a chain system that cannot be decoupled. There is then a clutch pack that power must go through from the transmission to get to the rear wheels. The only way I can see the claim "100% of power to either axle" being true is if you take into account the brakes on one axle being applied, momentarily, to stop the wheels on that axle. Then the power has no where to go but to the other axle.

I wonder if the xdrive system is different across all BMW models or if it's just computer programming.

DSC turned fully off is when the system really comes to life. I have jumped on and over a 3 foot snow berm with all seasons and it's unbelievably tenacious.

[Hobbe74]

Originally Posted by DJKhan85

I normally hate browsing these AWD threads since most people have no idea how any of the AWD systems actually work. Instead they just believe the marketing hype that gets played by the individual companies. I am glad that your post proves people still go out there and do hard research on AWD systems.

Most of the AWD systems rely heavily on computer intervention (except for the aforementioned STI, which is different than the other subaru AWD systems). The computer will either cut power, open/close a clutch that controls power to the rear wheels (as does xdrive, at least the versions I read about in the 2008 models) or brake wheel(s) to get the power where the computer determines it should be sent.

From what I recall the xdrive system has the front axle connected to the output of the transmission via a chain system that cannot be decoupled. There is then a clutch pack that power must go through from the transmission to get to the rear wheels. The only way I can see the claim "100% of power to either axle" being true is if you take into account the brakes on one axle being applied, momentarily, to stop the wheels on that axle. Then the power has no where to go but to the other axle.

I wonder if the xdrive system is different across all BMW models or if it's just computer programming.

Well said.
I'm not 100% sure due to memory loss but as i recall the key is after 2008 models its an electronically controlled multi-plate clutch that makes the difference compared to older, or other systems, in terms of system speed when distributing power between axles.

[zipstic]

Originally Posted by PackPride85

I didn't listen to the audio in the 2nd video, but these tests kinds of tests are completely bogus. Audi's system uses a Torsen (aka torque sensing) center diff. It's a purely mechanical set up that will multiply existing torque on one axle by some factor and transfer it to the other axle. The key is that there has to be some small amount of torque present or else 0 x 0 = 0. Despite that, its still a great system and is easy/cheap to implement. The transverse mounted audi's use haldex which is an xdrive type clutch setup.

Xdrive uses electronically activated clutches to engage the front axle (no true center diff), thus being able to transfer 100% of the torque to either axle even in 100% slip conditions (usually maintains a partial lock to maintain a rear bias of 60/40 I believe). Is it better than a torsen system? In the extremely unlikely event (and by that I mean impossible) that you have ZERO traction on BOTH wheels of an axle, then yes xdrive is superior. The fact that it uses sensors means it should be able to "detect" slippage before lost of traction (using steering angle, throttle, etc...)as well is another advantage.

What's really more important is the traction between wheels on each axle. Most of these cars with open diffs and traction control will brake the spinning wheel to transfer torque across the axle. My guess during this test was that they disabled that for the Audi and left it enabled on the BMW.

If you want a true performance AWD system look at a WRX STI. An adjustable viscous coupling center diff, which while slower to react can transmit torque in complete no slip situations, and torsen LSD diffs on the front and back (pre 2011). That setup blows the doors off xdrive and quattro.

Honestly, I think actual awd performance for quattro vs xdrive has more to do with how the DSC is programmed for same axle traction and tire size/type instead of how the power gets to each axle. If BMW wanted to throw an mechanical LSD or two along with Xdrive it probably would make a formidable performance AWD system.

This guy knows what he's talking about.

Audi's Torsen Quattro system (on all models except A3 and TT, which use a garbage Haldex system that VW and Volvo use) is purely mechanical whereas BMW's system is electronic. In my opinion, the 2nd video does not represent real world driving conditions and is purely for marketing, especially considering it was done at a BMW dealership. Someone else made the point that there is no mention of the traction control settings in the test either. Probably not a coincidence. After driving in snowy Minnesota with an Audi A4 and a BMW 335xi both equipped with snow tires, I would take the Audi hands down.

Oh, and don't forget that in terms of maintenance and reliability Audi never has issues whereas, although uncommon, you do hear about people having to replace their transfer case which is big $$.

[IEDEI]

Originally Posted by Asianoak

Second video is a great example of what makes xdrive so good in bad weather. Everybody loves to say that a good set of snow tires and a good driver is all you need and I used to stubbornly agree. Once I got an drive though I was a believer. Pulling out of an icy driveway with a foot of snow in it without shoveling is something I flat out couldn't have done in any of my rear wheel drive or front wheel drive vehicles. Once I'm moving then yes... Rear wheel drive with dedicated snow tires is fine... It's just that initial start that impresses me.

Didn't know it outsold quatro either.

drive a quattro someday....it makes a BMW xdrive model feel like its 2 wheel drive.

I would never drive an 'AWD BMW"......makes no sense. If i wanted AWD i'd go to those who do it best----Audi and Subaru.

[MattBianco]

A video of a few sliding around in slush: http://f15.bimmerpost.com/forums/sho....php?t=1084219

For some feedback on X Drive, I would troll the the X5 forum where users cover the pros and cons. This thread's video is a good, but merely a theoretical way of showing how X Drive works.

I have an LX470 and an X5. The latter is very good, but if there is three feet of snow on the ground I feel less confident in the X5.

[Mike_L]

Originally Posted by IEDEI

drive a quattro someday....it makes a BMW xdrive model feel like its 2 wheel drive.

I would never drive an 'AWD BMW"......makes no sense. If i wanted AWD i'd go to those who do it best----Audi and Subaru.

Not really. I had an A6 Quattro last winter and my xDrive 335GT this year, both on the same Continental DWS tires and they're definitely comparable. Both easily got out of their snowy graves with no issues and no shoveling. The BMW got a little sideways today while the Audi generally tracked straight, but they're both more than good enough.

[Peschiera]

Accidentally right now you can read on Autobild's online site the restults of a winter test of 10 AWD cars. Autobild itself says that they have compared apples to oranges Here is the ranking, starting with the best:
- Ram 1500
- BMW X435d
- Skoda Octavia Scout
- Jeep Cherokee
- Audi A6 Allroad quattro
- Fiat Panda 4x4 Cross
- Nissan Qashqai
- Toyota RAV4
- VW T5 Multivan
- Land Rover Defender

http://www.autobild.de/bilder/zehn-a...282.html#bild1

[burrito007]

Originally Posted by zipstic

This guy knows what he's talking about.

Audi's Torsen Quattro system (on all models except A3 and TT, which use a garbage Haldex system that VW and Volvo use) is purely mechanical whereas BMW's system is electronic. In my opinion, the 2nd video does not represent real world driving conditions and is purely for marketing, especially considering it was done at a BMW dealership. Someone else made the point that there is no mention of the traction control settings in the test either. Probably not a coincidence. After driving in snowy Minnesota with an Audi A4 and a BMW 335xi both equipped with snow tires, I would take the Audi hands down.

Oh, and don't forget that in terms of maintenance and reliability Audi never has issues whereas, although uncommon, you do hear about people having to replace their transfer case which is big $$.

Had an S4 with snows. now drive an X5. The 13,000 replacement S-tronic transmission is what drove me to turn in the S4. S4 was a bit better controlled in the snow, but haven't had a problem yet with X5 on all seasons.

oh and yeah and i had the torque vectoring sports-diff.

[///S65]

Originally Posted by Hobbe74

VW 4Motion is from Haldex, same as Volvo uses. FWD with help from rear if no or bad traction on front axle = so-so.
Audi uses more then one system, depending on model, but name them all Quattro.

Do you know if the Cayenne uses VW's AWD system? Or is it Porsche's own system?

[///S65]

Originally Posted by zipstic

This guy knows what he's talking about.

Audi's Torsen Quattro system (on all models except A3 and TT, which use a garbage Haldex system that VW and Volvo use) is purely mechanical whereas BMW's system is electronic. In my opinion, the 2nd video does not represent real world driving conditions and is purely for marketing, especially considering it was done at a BMW dealership. Someone else made the point that there is no mention of the traction control settings in the test either. Probably not a coincidence. After driving in snowy Minnesota with an Audi A4 and a BMW 335xi both equipped with snow tires, I would take the Audi hands down.

Oh, and don't forget that in terms of maintenance and reliability Audi never has issues whereas, although uncommon, you do hear about people having to replace their transfer case which is big $$.

I used to own a Q7 and I will never forget the "planted" feeling. The car is so stable and planted to the road. A lot of electronic stuff went wrong in the car including the whole MMI system. But the suspension and drivetrain were rock solid. Never had an issue with the mechanical stuff.

[PackPride85]

I think if I had to choose I'd go with the quattro system (the non-haldex one). A mechanical setup designed for a mostly neutral split. Purely electronic systems feel a bit "synthetic" to me. I'd still drive the BMW over the Audi in general though since xdrive is more than capable.

[ND40oz]

Originally Posted by Hobbe74

VW 4Motion is from Haldex, same as Volvo uses. FWD with help from rear if no or bad traction on front axle = so-so.
Audi uses more then one system, depending on model, but name them all Quattro.

Starting with gen 3 Haldex, it is now proactive and is no longer just FWD waiting for slippage to send power to the rear axle. It's all electronically controlled, just like xDrive and will send power to the rear axle depending on things like throttle position, incline, speed, etc. The TTRS, RS3 and RSQ3 don't seem to be too hampered using it.

[alpin325]

Originally Posted by ap1

I am not sure if that Audi use Torsen. Some quattro just like VW 4motion are using Haldex clutch too. What I believe the real trick is which wheel is touching the ground.

Audi's Quattro's major axle is front axle while BMW xDrive's major axle is rear axle. Torque are distributed to the other side as controlled by the clutch. If it was the front wheel that is touching the ground, the result is probably the reversed.

Shouldn't both systems work regardless if the front or rear wheel were on the ground...? Given it's a All wheel drive system... I'm learning.

[hwelvaar]

Originally Posted by Dackelone

Did you know that BMW sells more xDrive models per year, than Audi does it's Quattro models! Audi just markets it's Quattro system better than BMW does.

Dack

Source?

[Hobbe74]

Originally Posted by ///S65

Do you know if the Cayenne uses VW's AWD system? Or is it Porsche's own system?

I have no idea