quattro vs x-drive
05-04-2006, 12:57 AM
#11
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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.
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.
05-04-2006, 04:51 AM
#12
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.
05-04-2006, 05:03 AM
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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.
05-04-2006, 07:18 AM
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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.
<img src="http://images.consumerguide.com/cmsimages/articles/2005_Articles/aug05_articles/humvee%20and%20soldier_600.jpg">
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.
<img src="http://images.consumerguide.com/cmsimages/articles/2005_Articles/aug05_articles/humvee%20and%20soldier_600.jpg">
05-04-2006, 11:06 AM
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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.
05-04-2006, 05:08 PM
#20
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 )
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