mishar

Quattro is not all terrain transmission, but neither quadra is. Same thing with mechanical LSD of all kinds. Only real one is fully blocked all three differentials. Even that helps much more before the vehicle gets stacked.

Quattro, X-drive and 4-matic have also ESP (or similar) that should help in snow, but it's not magic. 50% of all those systems is a driver. So nose winch or this one.
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Brozee

Funny you say this as I did a fishtail in my subdivision with my Lexus and it got stuck in a neighbors front snow mound. Needless to say the Audi wouldn't have had an issue, well... besides ripping up their lawn lol. For what it's worth my 4.2L I still have in the stable has been amazing in the snow. Actually took it a month ago to a large open parking lot where all the hoodlums from the high school were drifting. Turned off the ESP and really showed them what the Audi and a proper V8 could do. Bit me in the *** as the whole next week I drove to and from work with snow caked in the wheels making the drive impossible. Mind you this was when it was in the negatives so car washes weren't an option.

dvs_dave

Older quattro transmissions had a manual rear diff lock which may have got you out of that situation assuming the other side had sufficient traction. However the newer quattro versions superseded this with cheaper to implement (an ESP system function) front and rear open diffs with Electronic Diff Locks (EDL).

The theory is that the spinning wheel is braked so transferring torque across to the other side. However if the other side has no traction also then no amount of diff locks would help, whatever their type. If you have insufficient traction on all 4 wheels then all you'll get is all 4 wheels spinning and you still going nowhere.

BASARAB

Yeah, but Jeep has 4lo, ability to lock both front and rear axle together Never had to use it though, but like having that option. Its a 2004 Overland, last year model they had solid axles, good for offroading, but not good for freeway driving.

So coming back to what I said, quattro (along with xdrive,4matic and others) is 99% good for regular road snow driving. What happened to me, was two wheels were on the road and two were in the ditch, not having any traction. Pretty rare occasion, but that was when quattro failed.

mishar

To amend what I said: it is not even for half off-road.

Mister Bally

My '87 5000CS quattro had both inter-axle and rear differential locks. Boy, I miss that car. 286,000 miles before donating her to charity. She served me well. And it had a 5 speed manual transmission.

bmwm750

This isn't about locking the front and rear axles together- it would be about locking the axles together SIDE to SIDE, a la differential locks. Unless your Jeep has locking diffs (at least in the rear), in the above scenario, your Jeep would be stuck as well.

As it has been pointed out, Audi's used to have a rear diff lock (WAY back in the day), which would help here. Many trucks use the Eaton G80 locking diff on the rear axle, which would help here. Hardcore off-roaders run various different brands of locking diffs, front and rear (and of course they have the transfer case locked front to rear).

The current version of Quattro works really well in 98% of on road driving, but it has its limits. The "electronic diff locking" whereby the ESP computer brakes the slipping wheel in an attempt to shift torque across the axle works reasonably well, as long as the difference in traction isn't 0% to 100% across the axle.

The most impressive AWD car that I have ever owned was a Subari WRX STi. Variable torque split from a base of 35/65 to 50/50 front to rear, with limited slip diffs in the rear AND the in the front.

The new Torsen III Quattro (40/60 base split) cars with the Sport Differential likely have an advantage here, as the Sport Diff has the mechanical ability to move torque across the rear axle without solely depending upon braking the slipping wheel. The front diff, however, is still open.

Remember, though- these are performance minded street cars. Not off-road trucks, and not rally cars. The STi was about as close as you could get to a street legal rally car, but still lacked the rear drive disconnect when you pull the e-brake (among a long list of things that "real" rally cars have- like a roll cage).

mishar

One of the most advertised features of Quattro is Torsen mid differential, but it is actually quite useless as LSD here. When one axle has zero traction other one doesn't move at all. Just like any opened differential, except it requires extra expensive oil. No wonder that others doesn't use it. Including newest Audis.

Problem with mud/snow traction is that only gentle movements work and none LSD works than. It has to be active and programmed for those purposes, probably switchable (intelligence necessary in order to distinct parallel parking from stacked in snow), or just fully locked. ESP has to work much smoother in order to help here. Just rough braking wheels with no traction makes rest of them to loose it.

bmwm750

A Torsen (whether T1, T2, or T3) is NOT a LSD- it never has been and anyone who knows better will not refer to one as an LSD. Same goes for a Quaife, as they use the same Gleason designed system as the Torsen. They are Torque Biasing Differentials, or TBDs. As such, they depend upon both wheels (or axles, if used in the center) having SOME traction- when this part of the equation isn't met, a TBD functions just like an open diff.

This is why in a true performance car, you want a clutch and ramp type LSD (or possibly one of the new, gerotor based units like the BMW M diff). If a wheel lifts while in a corner, you still get the same degree of lockup that you would were it still on the ground. LSDs also lockup on deceleration, which is especially useful in stabilizing mid and rear engine cars on braking. This is why all the fast Porsches you see on the track run clutch type LSDs.

Off road, as mentioned above, it's all about locking diffs- center (transfer case), and front/ rear lockers. What is a bit interesting here, however, is that the real Hummer is actually an AWD truck.

Crisis3

How'd my humble little post become an engineer's convention?