markcincinnati

The TorSen system used by Audi in many of their cars used to come with a 50-50 torque split. The Haldex AWD Audis (TT and A3) had F biased torque split, but would shift torque where it was needed. New iterations of TorSen (as early as the 2005 MY, as I recall) split the torque nominally at 40% F and 60% rear (and the weight balance is better, too -- still nose heavy but better.)

R biased AWD is sometimes said to be the holy grail of AWD systems (it is said mostly by marketing types but there is factual basis to back up the marketing scatology that is often written.)

The reason "serious" drivers like rear biased AWD or sometimes simply RWD is for handling performance. I was plenty pleased, frankly, with the 50-50 torque split of the old TorSen system, but I do understand that competitive forces pretty much dictate that Audi move to R biased AWD. And, like I said, there are legitimate reasons for R bias' claim to superiority.

There are thousands of entries all over the web that discuss the merits of R biased AWD and RWD generally -- for example:

"Audi AG unveiled in Germany this week a new-generation version of its landmark quattro all-wheel-drive system engineered to impart Audi’s AWD vehicles with handling that more closely replicates that of rear-wheel-drive vehicles.

New quattro system launches with high-performance Audi RS4 in Europe.

The new quattro system – launching with the high-performance RS4 sport sedan in Europe – under normal driving conditions “biases” 60% of drive torque to the rear axle and 40% to the front. Since quattro’s inception in 1980, Audi maintained a balanced 50/50 front/rear default torque distribution that it said imparted a high level of security and dynamic stability.

But the traditional 50/50 torque split also imparts quattro-equipped Audis with an inherent and safe understeering handling character that long has been judged dynamically inferior to vehicles – primarily luxury sport sedans – whose rear wheels do 100% of the driving.

Audi engineers, anxious to achieve dynamic parity with its RWD Mercedes and BMW (and now Lexus, Infiniti and Cadillac) rivals, have reengineered the quattro system to send 60% of engine power to the rear wheels, which they say is enough to deliver RWD-like handling while retaining the stable chassis dynamics and all-weather traction ability that were quattro’s original reason for being."

klik here for the full story (one of the 52,100 articles I was able to google up): http://www.euroteknik.com/forum/gene...attro-awd.html

Hopefully I have pointed you toward tons of information supportive of the merits of Rear-Biased Quattro (or AWD generally.)

Frankly, I think there are even more good things that can be said if one acquires an Audi that has Rear-Biased Quattro and Torque Vectoring (which Audi calls the "sport differential.") It is a shame, IMHO, that you can, at this point, only get the Audi Sport Differential in the A4 line on an S4. Why? This feature almost magically reduces understeer to near zero. I would think the more run of the mill A4 drivers would benefit from the ASD despite not having a super-charged V6 underhood.

Old Dog

Interesting read. Thanks. I was under the impression that all the A4/B8s had the 40F/60R torque split until reading your post.

markinarch

I think you may have misunderstood his post (Or I am a dummy and am spreading false info). All B8's with quattro are 60/40 torque rear biased. The sport differential that changes the characteristics of the rear torque vectoring is what is not available for A4's. It is available on S4's and makes their rear end a little more slippery. Or something like that. I'm not positive because I obviously don't have an S4 with that differential. Please correct me if I have made false statements.

Old Dog

After reading your post markinarch I went back and read markcinannati's post once again, and I believe it is the Old Dog that misunderstood. Yes, it seems if one gets the S-Line you have Torque Vectoring.

Thanks for straightening me out .

JD15

You're correct. The rear differential is similar to the SH-AWD system in Acuras; it distributes torque from side-to-side, in addition to front-to-rear, as in traditional AWD systems. During a sharpturn, it sends most of the torque to the outside rear wheel, "pushing" the car through the turn and mostly eliminating understeer. All B8s, however, have the 40/60 F/R torque split.

markcincinnati

All A4+S4 B8 quattros come with 40% F 60% R torque bias. S4's alone in the B8 iteration (at this point) offer ASD which is the torque vectoring rear diff. An S-Line A4 and S4 are not the same car.

Torsen's, generally speaking, brief history in Audis:

50-50 torque split and the ability to shift power from front to rear in real time to 2005

40-60 torque split and the same f/r power shift ability in selected Audis from 2005 forward

Some "quattros" -- the TT comes to mind -- used the Haldex system, which was fwd biased, but would still shift power to the rear or front as needed (although Haldex reacts where Torsen "binds in real-time" making Torsen a nano second or three quicker in putting the power where it is needed when it is needed.) Torsen is a bit heavier than some other AWD systems -- it works mechanically, meaning it does not have to wait to be sent a signal indicating traction issues, react and send a command back indicating the proper actions.