Bknewtype

Since we r on the topic of memory and mmi settings, can anyone tell me why my car wont ever start in S mode when i put it in drive? I have it set to individual ( dynamic everything except engine noise) and its always on D unless i pull it down or press the drive select again to select individual.

J. Patterson

Guys. Great discussion of Haldex vs Torsen diff Quattro. ( and to think it all started with memory seats! ). I have one of each and have tracked the old Haldex TT for several thousand track laps. Just remember that the Haldex cars are different. The front wheels are 100% engaged all the time. While the rear axle is "preengaged" all the time to a degree by those clutches, the only way a rear wheel can provide ANY torque or force is if a front wheel slips. THEN it depends on how much traction is at front to determine how much of the remaining torque is provided by the rear wheels when the Haldex clutches lock the two axles together. It CAN be 100 % at either end. The Haldex controller just decides how tightly and how quickly to lock those clutches. A Torsen car like my S5 DIVIDES the torque between the axles. (40% f 60% r) A loss of traction at one end will reduce the torque available at the other end also. ( ASR overcomes some of this by braking the spinning wheel). Two VERY different systems that in use achieve very similar results.

adg44

There has been so much misinformation and incorrect claims in this thread regarding Haldex and torque distribution and what percentage is driving the rear wheels. This is a very complex and confusing subject, so to keep it as simple as possible:

1) Audi specific programming in the TT and TTS (and now the S3) adjusts torque split via Audi drive select. In Dynamic mode, the ESC system will not reduce power in cases where the wheels start slipping, and will allow oversteer.
2) When the rear clutch is fully engaged, power will flow naturally during acceleration. When you are accelerating, power is flowing more towards the rear than the front. This is natural physics.
3) Don't get so caught up on torque split. This is not a self-locking center differential that has limits with how much torque can be sent front to rear, or has a pre-defined initial torque split. It is constantly varying where the power flows.
4) 5th gen Haldex is always driving the rear wheels. There is no "efficiency" mode of drive select for the US, so it never disengages the rear wheels.

Don't worry about it so much and go out and enjoy your cars.

Hope this helps...

grey67

Good advice adg44. I am sooooo looking forward to my mistress' arrival.

J. Patterson

Agreed. Even when I re read my own post I see parts where I realize " That's not quite right".
I think most of the confusion lies in trying to descibe or assign a percentage torque split to a drive system where that just does not apply. Even Audi has been guilty of this. Regardless, it works and under some conditions can be superior to conventional Quattro with a center diff.

Tailwagger

It does. But if there are hard answers, I'd like to far better understand whats going on here. I don't know how much experience you have driving the TT, but it is not unheard of to experience the rear end stepping out somewhat unexpectedly. On my very first test drive in a TT in a down hill, slightly off camber, decreasing radius, on ramp under modestly aggressive power, I got a taste of it. All the forces where building quite smoothly, when pop, out steps the rear, snap goes the ESC to drag things back in line. This was not bump induced, the road surface was consistent. Even though I was not pushing particularly hard given the salesman was riding shot gun, those circumstances created a perfect storm in that despite accelerating, the weight was more forward than usual (down hill) and with a decreasing radius, understeer even more inevitable. I recall thinking at the time, hmm, cool, this car can be playful after all, might be fun with the ESC off. Since that time, mostly from screwing around on snow days, I've become a bit more circumspect about it. And in fact, a similar observation was the origin for the previous time this subject heated up here in the form of the No fun thread.

The notion of the friction circle tells us that a tire can only offer up only so much grip, which if exceeded, regardless of whether its latitudinally or longitudinally, will result in slippage. Its seems fairly obvious from the circumstances mentioned, the rapid transition to oversteer is the result of the system deciding, for whatever reason, to vector too much torque, too quickly aft which, when the rears are under lateral load, abruptly breaks rear end grip. That strongly suggest to me, there wasn't a lot of longitudinal demand, ie. rear torque, being placed on the rear tires to begin with. That said, in the end as you state, who the hell cares? But what does matter a lot, at least to me, is finding the best combination of suspension, throttle and quattro settings to mitigate this behavior as being someone who likes to play occasionally play in those realms, it is both spooky and in no way confidence inspiring.

So the point of trying to characterize whats going on is precisely to be able to better enjoy the car. While silicon controlled decision making works quite well in many circumstances, it is by no means perfect. And often, particularly when at the limit of adhesion, its desired solution interferes with those of the driver. As Sir Stirling Moss once remarked, "you use the steering wheel to present the car to the corner. Then you use the throttle to balance the car, to hold it on its limits." Having a third party, shuffling power F/R aggressively makes achieving that balance more difficult. I'd offer that given the TTS/S3 unified brain you mention, it would seem that those programming the system perhaps should be paying closer attention to the yaw sensors when deciding how rapidly to shift power around. I'm hopeful that over time these algorithms will, or at least could, get better at working more surreptitiously. In the meantime, I'd postulate that when handling, not acceleration, is the priority, despite being somewhat counterintuitive, selecting dynamic mode for quattro is likely not the best choice given a preference that the system shuffle power in the smoothest and most predicable manner possible.

Perhaps the ex-racer in me is prone to over rotating when it comes to wishing for an optimal setup, but I prefer to know rather than find out the hard way that I've guessed wrong. So, if you or others have docs or more info, etc, and as the thread I expected on this subject resulting from the No Fun thread never materialized, I think as least some of us would profit if it finally did. I know I would read it with interest.