quattro vs x-drive - AudiWorld Forums

Go Back   AudiWorld Forums > Audi Models > Audi A8 / S8 > A8 / S8 (D2 Platform) Discussion
Sign in using an external account
Register Forgot Password?


A8 / S8 (D2 Platform) Discussion Discussion forum for the D2 Audi A8 and S8 produced from 1994-2002

quattro vs x-drive

Reply
 
 
 
 
LinkBack Thread Tools Search this Thread
Old 05-03-2006, 12:21 PM   #1
AudiWorld Member
 
Join Date: Oct 2003
Location: mass
Posts: 135
Default quattro vs x-drive

I saw this video on Google Video. I cant believe that the A8 is unable to get off the rollers without assistance.
__________________
1992 Mercedes 300E
2000 Acura Integra
2001 A8L - Ming Blue
2008 Toyota Prius
quattro100 is offline   Reply With Quote
Old 05-03-2006, 12:38 PM   #2
AudiWorld Super User
 
Join Date: Jun 2004
Posts: 2,436
Default Thats a little shady....I'll tell you of something really stupid I did, but Audi Quattro saved me.

I had my A8 on the car carrier on my move to OH last year. Upon arriving at my new home, I went to unload my car. Stupid me overlooked the fact that I had to pull the wheel ramps from the car trailer to the ground. It was a heart stopping moment when I felt the car bottom out on the trailer! I didn't know what to do, so I put it in drive and drove forward so the rear wheels came back onto the trailer. No wheelspin, no drama, it just pulled the rear wheels back up. The front at first dragged the car forward a few inches, then the rear wheels kinda grabbed on. This was with my 19" wheels so the tires weren't so giving either on the corner of the trailer. I dunno why the A8 in that video didn't transfer the power to the front. They might have tweaked it.
__________________
Gone:


Now:



<a href="http://pictureposter.audiworld.com/77296/100_0270t.jpg">
My custom paddle shifter</a>
<a href="http://forums.audiworld.com/a8/msgs/128171.phtml">
* Washer Fluid Sensor Fix</a>
<a href="http://forums.audiworld.com/a8/msgs/104786.phtml">
Memory Seat Set Procedure</a>

Current Rides:
2005 BMW 525i - 18" Polished Breyton Flame Wheels

Past Rides:
02 S2000 New Formula Red/Blk
97 A8Q Pearl/Blk ..201K miles!
98 S70 Teal/Tan
here was a rough transition : -)
92 300zx Black/Tan
92 240sx Juniper Grn/Tan
89 Probe GT (first car) White/Red (yuck!)

ex-a8drifter is offline   Reply With Quote
Old 05-03-2006, 12:39 PM   #3
AudiWorld Senior Member
 
Join Date: Jan 2001
Posts: 1,885
Default What happens to nose-heavy cars with no rear-biased quattro?

It's surprising, though, and doesn't seem to make sense. Shouldn't quattro pick-up rear-wheel spin and transfer to the front wheels? A problem with the limited-slip differential on the Audi? Who produced this video?
__________________


2001 Audi S8
2007 Audi S4 Cabrio
2004 Lexus GX470
2006 Saab 93 Aero Cabrio
dimitristx is offline   Reply With Quote
Old 05-03-2006, 01:31 PM   #4
Elder Member
 
Join Date: Mar 2001
Posts: 11,968
Default The video correctly shows what to expect.

The center differential in the Audi is a Torsen without the locking feature. Normally torque is split equally front-to-back. Under low friction conditions, torque can be split up to 2:1 or 1:2 front to back. In the situation shown in the video, the maximum torque that can be utilized in the rear is zero. Since two times zero is zero, zero torque gets transferred to the front, and the car is stuck.

Note the "Total Tractive Effort" at the lower left of the chart. The Torsen behaves exactly like an an open in this situation, zero front and zero back when surface friction coefficient is zero.



The BMW must have a locking differential, either mechanical locked based on wheelspin, or a viscous coupling (as used in many Range Rovers.
__________________

2001 Audi S8
2007 Toyota FJ Cruiser
ryoung is offline   Reply With Quote
Old 05-03-2006, 01:36 PM   #5
Elder Member
 
Join Date: Mar 2001
Posts: 11,968
Default Re: Rear Differential

The traction control system will use the ABS system to brake a spinning wheel when it detects a speed difference across the two rear (or two front) wheels. In this case, however, both rear wheels are happily spinning at the same speed, and the traction control system has nothing to do.
__________________

2001 Audi S8
2007 Toyota FJ Cruiser
ryoung is offline   Reply With Quote
Old 05-03-2006, 02:31 PM   #6
AudiWorld Super User
 
Join Date: Jul 2005
Posts: 8,039
Default the same thing happens to allroads if one wheel leaves the ground

__________________

Angus Beef is offline   Reply With Quote
Old 05-03-2006, 08:41 PM   #7
AudiWorld Super User
 
tozoM8's Avatar
 
Join Date: Sep 2004
Posts: 6,628
Default I don't get is. My center diff might be different, but the more gas I give the more it locks up.

If I turn slowly on the parking lot, everything is smooth, but if I step on it the whole car shakes and all four tires spin at the same speed. I've tried it with two wheels on ice. With little gas the two wheels on the ice was spinning. With full throttle it locked all the wheels and went forward without feeling the ice at all.
__________________
'05 Porsche Cayenne Turbo titanium on black
'01 black on black allroad 2.7T
'01 black on black A4 1.8T 5MT
----------------------------------------------------------------------
'01 black on black twin turbo S8 6 speed manual(euro TDI 6th gear), RNS-E, Passport SRX SOLD
tozoM8 is offline   Reply With Quote
Old 05-03-2006, 10:54 PM   #8
Audiworld Junior Member
 
Join Date: Mar 2006
Location: San Diego, Ca
Posts: 74
Default Lame. No one would just lay on the gas in this situation. Wouldn't

applying pressure to the brakes while accelerating fix this?
__________________
1998 A4 2.8 quattro (252,000+ miles)
RonsB5nB6 is offline   Reply With Quote
Old 05-03-2006, 11:10 PM   #9
Junior Member
 
Join Date: Oct 2000
Posts: 950
Default Finally a reason for heavy wheels

Spinning them up to a specific rpm requires more torque, or torque for a longer time, resulting in the same being delivered to the other end of the car.

Seriously, can't ASR apply brakes to two spinning wheels, albeit while cutting engine power, thereby giving Torsen something to react against? I thought EDL was a separate side-to-side program, differing from ASR in not being switchable and operating over different speed ranges.

Tom
ttuling is offline   Reply With Quote
Old 05-04-2006, 12:49 AM   #10
AudiWorld Senior Member
 
Join Date: Mar 2003
Posts: 1,184
Default the torsen is "locking"

it locks until it hits the bias ratio (torque split across the diff), where it unlocks and allows differentiation in the same manner as a limited slip differential. this is what is shown in the graph you reference.

edl is also used to control the torque bias shift across the centre differential to limit the biasing effect, but the primary determinate is the bias ratio - relatively low (3:1) on our torsens as they are mainly designed for good traction. high bias torsens (5:1) are available and have been used by some to limit understeer (e.g. statis racing).

fwiw, the centre differential in the latest quattros is entirely different from our cars, it has a combination of an epicyclic diff with a torsen, in a similar manner to a viscous coupling (as opposed to a viscous diff). it is called the torsen-c.
__________________
dave
'03 rs6
'04 allroad tdi

skiwi is offline   Reply With Quote
Old 05-04-2006, 12:57 AM   #11
AudiWorld Senior Member
 
Join Date: Mar 2003
Posts: 1,184
Default the torsen will work

unless, as randy says, there is 0 traction at the rear. btw, 0 is a very low number, normal ice has a cof of around 0.2...

but it is my understanding that edl will work across the centre differential and so kick in in this sort of situation. but as we don't get snow in northern nz, i haven't been able to test it.

a locking centre differential allows full torque split accross it, and in this situation, most of the torque would be sent to the front. which is what you want from an suv. our cars are not suv's. a multiplate clutch differential, particulalry the later model "active' ones will also differentiate torque to the fronts in these situations.

fwiw, the old audi v8 (the d1) had a model with a multi-plate clutch in the centre, also a model with torsens in the centre and rear.
__________________
dave
'03 rs6
'04 allroad tdi

skiwi is offline   Reply With Quote
Old 05-04-2006, 04:51 AM   #12
AudiWorld Super User
 
Join Date: Jun 2004
Posts: 2,436
Default Thats a good point, I think thats what I did in my brain fart situation. I held the brake so as not

to rocket off the car trailer. I used it to modulate the forward movement. I did it unknowingly and maybe thats the solution.
__________________
Gone:


Now:



<a href="http://pictureposter.audiworld.com/77296/100_0270t.jpg">
My custom paddle shifter</a>
<a href="http://forums.audiworld.com/a8/msgs/128171.phtml">
* Washer Fluid Sensor Fix</a>
<a href="http://forums.audiworld.com/a8/msgs/104786.phtml">
Memory Seat Set Procedure</a>

Current Rides:
2005 BMW 525i - 18" Polished Breyton Flame Wheels

Past Rides:
02 S2000 New Formula Red/Blk
97 A8Q Pearl/Blk ..201K miles!
98 S70 Teal/Tan
here was a rough transition : -)
92 300zx Black/Tan
92 240sx Juniper Grn/Tan
89 Probe GT (first car) White/Red (yuck!)

ex-a8drifter is offline   Reply With Quote
Old 05-04-2006, 05:03 AM   #13
Member
 
Join Date: Apr 2006
Posts: 1,850
Default Re: Thats a little shady....I'll tell you of something really stupid I did, but Audi Quattro saved m

Great story! As an unfortunate soul with [too] many moves under my belt, I can attest to the state of mind you can find yourself in, especially if there is family along.
__________________
jazbo123
98 A8Q
jazbo123 is offline   Reply With Quote
Old 05-04-2006, 07:16 AM   #14
AudiWorld Senior Member
 
Join Date: Jan 2001
Posts: 1,885
Default doesn't the new A3 use a Haldex center differential?

__________________


2001 Audi S8
2007 Audi S4 Cabrio
2004 Lexus GX470
2006 Saab 93 Aero Cabrio
dimitristx is offline   Reply With Quote
Old 05-04-2006, 07:18 AM   #15
Elder Member
 
Join Date: Mar 2001
Posts: 11,968
Default Re: applying the brakes

I almost forgot. Back in 1990 I had a chance to spend 4 hours in a "new" HUMVEE (w/o the ma duce) on AM General's off-road course in Mishawaka Indiana.

The original HUMVEE uses the same 2:1 bias Torsen as the A8/S8, but in the front and rear differentials. The center differential was a standard open type (though it could be locked). Even with the center diff locked, one wheel spinning front and back means the vehicle is stuck. When this occurs, the standard procedure is to apply the brakes more-or-less in proportion to the throttle. Once the brakes apply torque to stop the spinning wheel, the other wheel across the axle gets 2X this torque, and off you go.

Unfortunately, this probably doesn't work for long with the A8/S8. Audi's idiot proof drive-by-wire kills the throttle very quickly after the brakes are applied.

__________________

2001 Audi S8
2007 Toyota FJ Cruiser
ryoung is offline   Reply With Quote
Old 05-04-2006, 11:06 AM   #16
AudiWorld Senior Member
 
Join Date: Mar 2003
Posts: 1,184
Default correct

the haldex will lock completely with enough slip. the new generation of haldex coupling (used by volvo) has a "pre-charge" function that will allow a full lock without any slip.
__________________
dave
'03 rs6
'04 allroad tdi

skiwi is offline   Reply With Quote
Old 05-04-2006, 01:08 PM   #17
AudiWorld Super User
 
'01 S4 Kid's Avatar
 
Join Date: Jun 2004
Location: philly suburbs
Posts: 2,803
Default well you don't really know that both wheels are spinning...

__________________
'01 S4 gone, sorely missed, waiting to be replaced
2008 VW GTI Black Magic/Interlagos, 6MT, no sunroof
-B&G Coilovers
-Hufeisen wheels
-Carbonio intake
-Revo stage 1
-tinted everything, R32 style tails
-plenty of other small cosmetic things
'01 S4 Kid is offline   Reply With Quote
Old 05-04-2006, 02:11 PM   #18
AudiWorld Super User
 
Join Date: Apr 2003
Posts: 2,300
Default blah blah blah. When BMW takes away Audi's Rally crown ...

... with their "superior" AWD, I'll believe the spew of sideway-baseball-hat-wearing BMW boys.
__________________
-------------------------------------

18" 2006 Soft 5-Spokes - Goodyear F1s - Milltek Exhaust - Clear Sides &amp; Corners
Jkay is offline   Reply With Quote
Old 05-04-2006, 02:34 PM   #19
AudiWorld Super User
 
'01 S4 Kid's Avatar
 
Join Date: Jun 2004
Location: philly suburbs
Posts: 2,803
Default hahahahaha best phrase ever!!!!

i got a friend who is/was the exact person you imagine
__________________
'01 S4 gone, sorely missed, waiting to be replaced
2008 VW GTI Black Magic/Interlagos, 6MT, no sunroof
-B&G Coilovers
-Hufeisen wheels
-Carbonio intake
-Revo stage 1
-tinted everything, R32 style tails
-plenty of other small cosmetic things
'01 S4 Kid is offline   Reply With Quote
Old 05-04-2006, 05:08 PM   #20
AudiWorld Super User
 
tozoM8's Avatar
 
Join Date: Sep 2004
Posts: 6,628
Default BMW computer controlled AWD is really good at crawling speed. However

like Jkay said, they are not there yet. Audi have to keep developing Quattro, because there are new GOOD AWD systems out ( Lexus, Infinity )
__________________
'05 Porsche Cayenne Turbo titanium on black
'01 black on black allroad 2.7T
'01 black on black A4 1.8T 5MT
----------------------------------------------------------------------
'01 black on black twin turbo S8 6 speed manual(euro TDI 6th gear), RNS-E, Passport SRX SOLD
tozoM8 is offline   Reply With Quote
Old 05-04-2006, 05:08 PM
AudiWorld
Audi R8




Paid Advertisement
 
 
 
Reply

Tags
allroad, audi, magic, quattro, rear, spinning, video, wheels, xdrive

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -8. The time now is 02:13 PM.


Copyright 2014 AudiWorld.com Audi Enthusiast Community