one time driving to a hilly are in the city in an 8" snow, in a RWD,
I decided to take a street that was a more gradual hill than the
usual, which was mighty steep, and got stopped half way up. A bus was
spinning its wheels at the top of the hill. Headlights came up behind
me, and kept getting closer, and next thing their bumper was on mine,
pushing me up over the hill. It was a city cop in a Jeep, I believe an
old Cherokee. When  I got near where I was going, to see a GF who
didn't want to drive in the snow. I couldn't get up the hill there. I
Turned Around and Backed up the hill, like there wasn't any snow.
Guess I made it a sorta  FrWD.

VF

No they are not. One of the most important differences is whether the system
is a 4WD (ie mostly FWD or RWD) or partial AWD or full-time AWD.

Audi Quattro, Mitsubishi AWD (Talon/Eclipse/Lancer EVO series) are all
fulltime AWD with a center differential action, as AFAIK the various types
of Subaru AWD. All these are  (AFAIK) 50/50 torque split with the exception
of some older Mitsu's which are 65/35 F/R.

The center diff is generally lockable in some fashion. Mitsu and some Subaru
use a viscous coupler. Other Subaru's use a wet clutch system with
electronic control. EVO's and WRX use (AFAIK) a Torsen torque split system.
The advantage here is that when one end starts to slip, the centre locks up
gradually.

Older Subaru and Mitsu used a simple Front/Rear lock system ie 4WD not AWD.
Some have a viscous front diff too.

EVO and WRX have locking rear diffs, the base models don't usually unless
optioned.

Then there's the Honda CRV system that's about 70/30 split, with a hydraulic
clutch system in the rear diff that locks up gradually. ie the CRV is really
FWD with occasional AWD.

The Chrysler/GM minivan systems use a system that runs off one side of the
front diff, and it only works because the ABS system also handles the
traction control. Torque split is about 80/20 at best, and they really are
FWD system with pretentions of being AWD according ot the marketting
departments.

There's the BMW system and Jaguar systems about which I know nothing  at
present. Anyone?

Lets not forget Jeep Quadratrack. Anyone?

SD

Curious as to what the Audi did different, and whether autos or
manuals?

VF

If you meant 4WD for fast cars (like the Impreza STI) the Mitsubishi
Evo has an even better system. But I think you meant slower cars.

Attention: only the longitudinal engined Audis have a center differential.
The transverse engined* ones (A3, TT) have an Haldex system (based in a clutch)
even when called "Quattro" which have issues** with the traction control.

[* BTW, this is an Audi/VW choice, not a technical need. Mitsubishi with the
Evo, Lancia with the old Delta Integrale, etc. didn't have any problem
fitting a center diff in the transverse gearbox.]

[** The clutch can only send power to the rear axle if it detects
slipping of the front wheels. But if it detects slipping the traction
control will brake the front wheels or slow the engine to stop the
slipping. There have been cars (IIRC a Renault Scenic some years ago)
in which the system simply didn't work (I suppose it was a victory of
marketing over engineering). ]

4WD systems can have (in increasing order of sophistication):

- a mechanical rigid connection between the front and rear axles.
This is the classical system (partial time 4wd). Can only be engaged
in slipping conditions. I think most pickups still use it.

- some kind of clutch (electronic controlled or viscous coupling)
between the front and rear axles. As I said above it has issues with
the traction control system and it also means some waste of energy
in normal conditions since the two axles need to rotate at different
speeds in corners. I think many manufacturers are using it now (Volvo,
BMW ?) and I have read here that some of the Subarus also have it.

- a center differential. This is the proper solution, because it can send
torque to all wheels _before_ they start slipping but then it also needs
some kind of locking (LSD, Torsen, manual locking, traction control)
for difficult conditions.

For off-road low-range gears are also useful.

I currently drive Jeeps (both CommandTrac and SelecTrac), formerly a Pontiac
Sunrunner (which is a Suzuki Sidekick) and Subarus (Forester currently and
Impreza previously) which are a good cross-section of full time 4WD,
part-time 4WD, and AWD, and not really surprisingly like Subarus the
best...but my FAVOURITE winter cars were my 65 Corvairs (coupe and convert
with autos) and 66 convert (with 4 sp).
-I once drove 35 miles/60 km in the 65 Coupe when there was 3 FEET of fresh
soft snow, ie to bottom of side window. Under those conditions, the front
end lifted off the ground and the wheels acted at 'rudders', and the rear
wheels dug down. At about 15 mph/25 kph, it acted like a motorboat, and
handled accordingly. Back off the throttle, and the front went down, exactly
like a motorboat. On that particular 'necessity' trip, I was one of three
vehicles on the road over 3 hours, and the other two were monster trucks
with balloon tires and 2-3 ft ground clearance.
-I once pushed a police cruiser up a 5% icy hill with my 65 convertible with
just a tied rimless tire as the pushing cushion.
-I regularly "parked" my convertibles nose in, in shallow ditches when
regular parking spaces vanished in mid-winter...can't remember how many
times people wondered if I needed a tow truck, but I just got in, shoved it
in reverse, and backed out--never ever got stuck in Corvairs with big snow
tires on them--and with stiff shocks, good radials and the right air
pressure, they were just amazing in summer

Anyone know from personal experience if the Suzuki SX4 AWD 5 door hatchback
m/t is as competent as a Subaru Impreza 5 door hatchback m/t?

Jim on PEI

On Jan 3, 1:49 pm, "Fred Boer" <fredbo...@NOyahooSPAM.com> wrote:

Don't have experience with other AWD systems, but have owned a
Pathfinder, Cherokee and Samurai, all with 4WD, low range and manual
transmissions, and they were all very competent in snow, especially
deep snow with their high ground clearance.  However, the reason I'm
posting is to say that my all time favorite "snow-mobile" was a 1965
Corvair.  With 65% of its weight over the rear wheels, a limited slip
differential and quality snow tires, it was absolutely unstoppable,
despite the fact that I had lowered it about an inch for
autocrossing.  In deep snow, you just rammed through it until you
carved a path.  Used to go looking for the steepest hills I could
find, and there are quite a few here in the Hudson valley, and it
NEVER found one it couldn't handle.  Only problem I ever had was an
ice rut that put a hole in my gas tank.  What makes the Subaru a so
attractive to me is performance on any slick surface, especially when
equipped with tires that perform well in rain (not the original
equipment Bridgestones).  With power distributed back to front and
side to side, it's never at a loss for traction and immune to torque
steer.  Even on ice, where the conventional wisdom is that AWD
provides no advantage, it gives you four driven wheels instead of two
to catch a piece of dry pavement.