rsilvers129

A paddle shifter that will automatically shift for you is 100% pointless. They may as well not even put the paddles on the car. I have not really explored that on my A4, but I did notice that it seems to not shift for me when in sport mode, and I have always been in dynamic so far. I will try it some time.

superswiss

Well, in Audi's mind it's a safety feature for the average owner, who probably never drove a manual transmission and therefore would completely panic if the car ran into the rev limiter if they forget to shift in manual mode. That's basically one aspect that I meant by the S-tronic feels more like a traditional automatic in the A4. The Tiptronic also upshifts automatically even in manual mode, except again in the RS implementations such as the RS7 and the new RS5. Basically Audi Sport chooses a programming that's more in line with manual transmissions, whereas Audi chooses a programming more inline with traditional automatics for the mainstream consumer.

rsilvers129

Will it let you stall it if you don't downshift?

superswiss

No, that it won't. It will automatically downshift to avoid stalling or lugging the engine.

audi8k

The 50/50 split, for a differential gearbox on 'open' mode, is true only for symmetric differential. It is my understanding that a TORSEN type 3 and the Audi 'Crown Wheel" diff is assymetric in order to (in open mode) split the torque close to 40/60. The "more than lock it" statement from Kronstorfer is not relevant when the diff is in open mode and for a completely locked differential the torque split is only given by the (counter) forces from the front and rear axles.
Another important difference between having a mid-diff or not is that the TORSEN differential is AWD also when there is no wheel slippage. It doesn't even have to 'bind'. The 'binding' makes the difference between a TORSEN and an open diff when the torque reaches the limit of counter force from one of the axles.

audi8k

I have use for the paddles, anyway. I agree that the response time (A4 3.0TFSI S-tronic) is too long, especially in the case when the prepared gear in the unused 'half' is not what I want. (It shifts a lot faster when I shift in the direction the electronics has prepared.) But the paddles makes it possible, also in automatic mode, to prepare the right gear before it is needed.

markcincinnati

Yes Torsen Quattro does mean AWD all the time. What I mean, regarding binding, is that the Torsen diff has a distribution, normally, of 40% F 60% R. However, it is possible for the torque to redistribute due to traction circumstances. What differentiates Torsen is that when power redistribution occurs the "binding" that makes this possible is NOT a reaction -- a split second "after" -- it is a real-time action. The mechanical nature of the Torsen and how it reallocates the "dominance" of torque (front to rear, rear to front) is why there is zero latency.

I will grant, however, that a reactive system, such as Ultra, reacts so quickly as to be "virtually" real-time, "virtually" lag-free. However, there is a difference between "very little" latency and zero latency. My ability to know when this latency occurs may be "suspect" -- however, part of what we have been discussing does have to do with the psychological aspects of "Torsen Quattro" vs. "Ultra Quattro." We are, apparently, in violent agreement.

NorthwestB9

I disagree with your whole assessment. Torsen may indeed have a 40/60 front/back split, BUT when it comes to reallocating torque, it is fully reactive. It doesn't know to reallocate torque to the front or rear wheels at higher/lower than 40/60 until after the wheels slip. So yes, it may be in AWD mode all the time, but the torque reallocation takes LONGER than it does under Ultra because it doesn't have the reaction time, nor does it have the proactive elements of Ultra. Ultra knows the road conditions and can create a model of the road ahead. If it detects ice, even before the wheels slip, the computer can begin reallocating torque before it's needed. Now we can debate on how well the computer predicts the reallocation, but it does take place earlier than it would under Torsen. And in a reaction situation, the 200ms is still faster than Torsen can reallocate. Torsen would have the advantage if the Ultra computer is taken completely by surprise when there is unexpected wheel slippage in which case the 40/60 will be better than 100/0, but the Ultra can still react faster.

You contend Ultra is a fully reactive system. It is not. That's where your assessment is incorrect. The Haldex systems in the A3-RS3 are indeed reactive, but the Ultra is not the same system.

rsilvers129

Here is what I can determine from reading around. Torsen-style doesn't do much to reallocate torque. It is either torque-biased 40/60 with the potential for front and rear shafts at different rpms, or locked to 50/50 like Haldex or Ultra.

Ultra when cruising along is in 2WD mode behaves like a FWD car and is 100/0. When engaged and under some duress, it is 50/50 and behaves like Haldex. So worst case, it behaves like FWD. Best case, it feels like Haldex - and since it is on by default at rest, acceleration feels like Haldex.

Torsen-style is normally cruising along in 40/60 mode. and behaves somewhat like a RWD car (but not as much as the Crown Gear does). If there is some wheel slip, it can lock to 50/50 mode, and behaves like Haldex . But the default at rest is 40/60 and feels somewhat like RWD car.

For side to side, both Torsen-style and Ultra are brake-based and reactive as they both have open front and rear diffs (except for the rear sport diff option).

AutoZine Technical School

"Torsen differential uses the special combination of worm gears and worm wheels to enable speed difference beween the two axles, whereas in case of slip it locks up automatically. Since it is a pure mechanical design, there is virtually no delay in its response. ""Performance-wise, the Quattro Ultra should be no better than Haldex system. In normal running there is negligible torque transferred to the rear axle, or even zero if the system has switched to FWD mode. When the ECU senses wheel slip or a demanding driving style, it re-engages the rear axle. The front multi-plate clutch will engage first, bringing the propshaft and rear differential up to speed and then the rear dog clutch closes to connect the rear wheels. Audi said this process takes at most 0.25 second. Such delay explains why it won't be adopted on performance models."
"One weakness of the original Torsen differential was its 50:50 torque distribution. It made the quattro cars notorious for understeer and dull handling (the Ur Quattro was the only exception perhaps). When JTEKT, the manufacturer of Torsen, developed a new variant with 40:60 torque split, Audi immediately adopted that on its 2005 RS4, followed by many other models."

Note that Ultra is back to the default 50:50 split that was "notorious for understeer and dull handling."

rsilvers129

Quattro Evolutions | awd cars, 4x4 vehicles, 4wd trucks, 4motion, quattro, xDrive, SH-AWD, Haldex, Torsen, wiki - How it works

"A torque split was changed on this vehicle to improve handling. Previous quattro generations were criticized for their unstable behavior in slippery conditions, where the car's behavior could suddenly change from understeer to oversteer. Transferring more torque to the rear axle in quattro generation V gives a rear wheel drive-like feel."

"The purely mechanical operating principle guarantees maximum efficiency and no-delay response."

I am going to bet that it is hard to tell the difference between Torsen-style/QwU only in the sense that it is also hard to tell the difference between having the $2500 torque-vectoring sport differential or not having it. The difference is there for people who can tell, but most people can't tell.


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