cosmos

I know that the car is "all wheel drive", but is it inheriently front, or rear wheel drive? What is the split, if anyone knows?

Rob O

Quttro branded Haldex AWD system used on TT's (VW's 4-motion system) is FWD biased under normal use.

mm

As do most current quattro Audis save the TT and A3/S3...

stiles_s

Back when the b5s4 was introduced, there was some press release material that said it actually had a rear torque bias, as opposed to the 50/50 on the rest of the A4 line. I'll have to see if I can dig it up.

All you had to do was drive the A4 & S4 back to back to feel the difference -- especially in the wet. It was very real.

Just some useless trivia.

AdamD

There have been a lot of typos. Most recent I saw said the new S4 had a 70/30 f/r bias

Rob O

I don't remember (nor do I now feel) the S4 was/is in any way rear-biased compared to my A4 2.8 quattro, and I had the two together for a while.

Moreover, I have almost every US automotive publication from 1994-present. If you recall where you saw that press info, I'll gladly try and dig it up. I've not *ever* seen it printed that the quattro IV system, regardless of what model it was mounted in, was anything other than 50/50 under normal conditions.

mm

Many confuse weight distribution with AWD bias. Quattro IV is and has always been 50/50 for production cars IIRC.

stiles_s

From a guy who I consider a relative expert on AWD systems (not me, Eliot). You can see he's referencing "Performance Car" -- a British mag that tends to have better technical detail than our US fluff.

Power-on in the wet, the b5s4 has more of a RWD feel than the a4. Note that I felt this most readily in my wife's s4sedan, not my s4avant.

Just FWIW. I'd be interested in digging up some deep technical info on the b6s4...

=====================================

Re: new S4 has rear biased torque split!

--------------------------------------------------------------------------------

To: <quattro@coimbra.ans.net>
Subject: Re: new S4 has rear biased torque split!
From: "Yoon-Suk RAH" <vwaudi@nuri.net>
Date: Mon, 8 Dec 1997 02:50:57 +0900
Reply-To: "Yoon-Suk RAH" <vwaudi@nuri.net>
Sender: owner-quattro@coimbra.ans.net

--------------------------------------------------------------------------------

-----¿øº» ¸Þ½ÃÁö-----
º¸³½ »ç¶÷: eliot <eliot@eskimo.com>
¹Þ´Â »ç¶÷: quattro mailing list <quattro@coimbra.ans.net>
ÂüÁ¶: northwest audi enthusiasts <audi-nw@u.washington.edu>
³¯Â¥: 1997³â 12¿ù 4ÀÏ ¸ñ¿äÀÏ ¿ÀÈÄ 3:48
Á¦¸ñ: new S4 has rear biased torque split!


>
>perhaps the various magazines have been too enchanted by the new S4's
>massive torque output to mention that for the very first time since 1980 a
>regular production quattro has a rear biased torque split of 46:54.
>(according to the current issue of performance car magazine, which has an
>excellent technical write up on the S4)
>
>the competition cars have been using rear biased splits for a long time
>but it took until now for us to see it on a road car. it must have been
>motivated by the huge output of the engine. i guess with a slight
>biasing to the rear powerslides are now more possible than before.
>
>the other less noteworthy development is that with quattro IV (i.e.
>quattro w/ 4WTC) the torsen's teeth has been blunted somewhat.
>
>old torsens had the gears cut such that torque splits of 78:22 were
>available. the torsens on the new cars have a less agressive 70:30
>maximum variation. i'd be interested in seeing how they use a torsen
>to do a rear biased split on the S4 since the torsen usually splits
>things 50-50 nominally.
>
>i guess that would also open up new aftermarket possibilities for hot rod
>1.8Ts too i suppose.
>
>
>eliot
>
>
>

I'v heard the ratio of torsen's distribution is up to its strength.

When I manage the Quattro Experience in Korea, Jan of 1995, I made a
question to staff from germany that why only the A8 4.2 used multi plate
type center differential(At that time, A8 4.2 used almost same center
differential as that of V8. But, from MY 1997, A8 4.2Q also has being used
TORSEN center differential.). His reply was "TORSEN cannot stand more than
250hp.".

Then, why does the 4.2Q use TORSEN again? Because it stand 300+hp now. What
does make that possible? The "Locking ratio" makes it possible. What is
"Locking ratio"? Locking ratio means the ratio of between the forces needed
for the worm gear to rotate the worm and vice versa. That is, the Locking
ration judges the power distribution ratio of TORSEN differential.

As eliot said, most of TORSEN differential in Audi Quattros can distribute
the engine power up to 78:22. That means the locking ration is 3.5:1. But,
in case of 4.2Q, its locking ratio is about 2.9:1. So its distribution ratio
is 65:35. Why is the distribution ratio reduced? As I told before, it is
because of the reliability. The bigger the ratio, the more stress on the
teeth of worm & worm gear. So, Audi cannot help without reducing the
distribution performance for the reliability. So, the distribution ratio of
S4 is the almost midpoint between ordinary Quattros and 4.2Q.

And, S4's rearward bias of power is - as far as I think - in order to
enhance the traction when acceleration. Because S4 has so much torque
comparing with its tire width and vehicle weight, its front tires may lose
grip when hard acceleration. In this case, center differential should WORK
to re-distribute engine touque. It must be a hard work for the TORSEN
differential, as we can see in the owner's manual, "if front & rear tires
have different radius, the TORSEN differential may damage or worn
prematually.". We can see the frt-rr torque bias in the lengendary Porsche
959, its distribution range is from 20:80 to 40:60.

If sombody in list know exact reasont for that, please let me know. I'll be
happy.

Thanks.

Rob O

That's the first time I've seen any reference to that effect, but the guy sounds like he knows what he's talking about. However, 46/54 is still pretty damn close to 50/50 and I'm not sure most people would detect a difference between the two torque splits. I guess when I think of an AWD system as being RWD biased, I imagine 40/60 (f/r) or greater.