hamproof

Might be old news for some folks, but good for passing time at work. Very insightful.

<a href=http://www.fortunecity.com/silverstone/lancia/58/technical_school/traction/tech_traction_4wd.htm>4WD Article</a>

larryV

I agree that that the 959's PSK system was the best ever but the rest almost sounds biased according to "critics interpretations"...

They fail to mention that haldex is really a 2-wheel biased system that is essentially 2 wheel drive until slip is detected. While this is not necessarily a bad thing, nothing beats the quick response of torsen. They also mention the non-variability of the torque split of torsen, which is very misleading since they are really only referring to the <b>initial</b> torque split. Obviously, torsen varies the torque distribution according to slip between front and rear. The initial torque split on any given car or any given application can be designed to fit the application by using the proper pitch of the worm gears. In the current non-haldex quattro systems, Audi uses worm gears that split initial torque 50:50 to fit the application they intended. The initial "bias" in the TT's haldex is not superior to torsen from a performance perspective. The only real advantage is lighter weight and compactness. Obviously, the "handling" merits they mention on haldex equipped VAG cars is attributed only to the cars lightweight design itself and the compactness of the haldex unit and not the effectiveness of the AWD system itself. Finally, the success of the rally cars which use the VC + differtial lock systems is not entirely due to the AWD system itself but to the cars used and the application. Those rally cars are successful because they are favored by the drivers as a car and not as an AWD system. Remember that Audi was banned from touring car racing because torsen was simply kicking butt all over the place. This was not entirely a case of torsen being a world beater but an AWD system applied perfectly to a racing application. same thing...

Rodney

If so, please provide a detailed comparison to torens based Quattro. The reason I ask is I am seriously considering trading in my A4 on a TT. I too was of the opinion that the Haldex system in the TT would produce a car that felt like a FWD car. However, after some research, talking to some TT drivers, and spending some time on the TT forum, that would not seem to be the case. Part of the reason is that the computer tricks the system. By getting input from the DBW signals and passing it on to the Haldex computer as it's being sent to the ECU, the Haldex computer (or portion of the ECU...I'm not clear as to whether Haldex gets its own box or what) can take preemptive action to transfer power BEFORE any slippage actually occurs. The result is that the TT behaves more like a RWD car than an AWD car (TT drivers regularly step the back end out by applying the throttle). From what folks have described, only at the very limits (11/10's for those who know what I'm talking about) does the TT even hint at having FWD characteristics.

Now, this is all second hand information. I'll be scheduling a TT test drive for the next time I bring my car in for service to see for myself. I'll post a review when I do.

Plasticar

I don't have any first hand experience, but I saw a display by Haldex at the 2000 SAE expo here in Detroit in March. What I remember, Haldex is an electronic vs. hydrolic system, it reacts much faster to slippage, and is lighter. I would be surprised if Haldex differentials are not incorporated in the next version of quattro.

larryV

...exhibits less understeer than the A4/S4 and I have no qualms about Haldex being an effective all-wheel drive system but my point is not the the effectiveness of car versus car but rather the all-wheel drive system itself to a given application.

I just wanted to point out how the article tends to generalize that haldex may phase out torsen because it is better. It's only better because of it's lighter weight and compact size. Understand that in the TT's case, power is at the front wheels until slip is detected by the haldex computer... kinda opposite of say a carrera 4's RWD bias system. I did not think the TT felt like a RWD car at all. In fact, at the limits on dry pavement, the A4/S4's torsen system felt easier and "safer" to drive. The TT had much better grip probably due to the lower center of gravity and less apparent body roll. However, it was also a bit sketchy when coming on throttle exiting a fast turn. If I wanted that kind of behavior, I would've just opted for all-out throttle-controlled oversteer and bought a 330

Rodney, don't get a TT roadster. Get a coupe instead. Handling is noticeably worse in the roadster with more body roll. I thought Audi would make such an open top more rigid. This doesn't seem to be a case. The roadster is a sloppy car.

Just my opinion.

Rodney

I can justify the coupe as being semi-practical as an only car, since it's top will provide comfort in the winter, and the rear "seats" can be used for extra storage space (either for gym bag/breif case, or folded down).

Basically, I'm becoming impatient with my plan to buy a used Porsche as a second car (that would be at least another year down the road beyond the TT, which is probably feasable this year). Plus I won't have a garage, so storing a second car could also be an issue. Just weighing my options, but would love to here more observations about how the TT compared to the A4/S4. Particularly things like ease of ingress/eagress (sp?) when wearing a suit.

larryV

ingress/egress even with a suit is fine with the TT. The TT 225 coupe's sport seats are actually more comfortable than the S4 sport seats and sits really low giving a more sporty feel. The main issue is visibility - you may have to seriously consider that. Before deciding on the S4 to replace my A4, I seriously considered a 225 coupe. I loved the car, especially the striking attention-grabbing exterior. The definite no-no's that I couldn't live with were poor visibility (especially rear and sides) and cabin noise. I guess I was also looking for more luxury and refinement. The S4's torquey biturbo sealed it for me but I still wish I could have both cars. In the twisties, there's no doubt the TT is more satisfying to drive. As a daily commuter and weekend highway cruiser/roadtripper, the S4 was better for me.

BOOSTD

Visibility is HORRIBLE, especially with the top up. Changing lanes and turning in traffic was a nightmare. Even on smooth pavement, everything in the car jittered and squeaked, and my lowered A4 w/17" wheels rides smooth as glass. While the interior is nice to look at, functionality is gone, case in point the window buttons. They're hidden behind the door handle, most likely because the door panel is completely flat. It also felt no faster than my chipped A4, probably because it weighs more. For $43K, I would take an S4 over the TT 225 any day. They're nice to look at, but for me that's all they're good for. I just couldn't have one as my daily driver.