ryans4

...quaife and pelican adapted the idea to a FWD Transverse type setup and I'm sure put a spin on it.

I know that quaife makes a special ATB that is helical, but has a lockup feature to counteract wheel spin issues in a helical based differential, but I also hear it's bank.

So I would say that a Quaife ATB (normal one) is a specific type of Torsen differential. I could be wrong though, i'm not the expert.

VonK :: Retired

Interesting. Thanks.

ryoung

And list some random thoughts ...

> You need to get near neutral in a steady state corner with springs and fine tune with bars.

> Turn-in (rotation) seems best handled with trail braking and/or shock tuning.

> As you said, a high bias center Torsen helps transmit power, important steady-state mid-corner but especially during full power corner exit.

> Rear LSD's are tricky on track, especially if you start with an inside tire in the air. What really works here except perhaps a locker?

> With a full throttle corner exit (assuming you don't start with a rear tire in the air), it seems that a front Torsen or Quaife differential can help as much as a limited slip in the rear.

The following table from <a href="https://forums.audiworld.com/a8/msgs/36145.phtml">Load Transfer Revisited</a> shows how much grip is available from each individual tire during various phases of a corner. I assumed an open center diff with a 50:50 split (I need to recalculate it with a Torsen's bias), but look at the "WOT exit" case. The inside front tire has the least grip of all, and of course, the car understeers. Wouldn't a front Torsen or Quaife reduce understeer? Or while we're at it, how about using three Torsens - center, front, and rear?

<img src="http://pictureposter.audiworld.com/17157/weightdistribution.jpg">

ryans4

...save for any "special" quaife rear ATB's, a normal Torsen is not what I would put in the rear.

A front Quaife ATB should be a good investment, but it would be the 3rd and last differential I bought for the Audi.

I'd do the higher bias center, then the rear LSD, then the front Quaife ATB.

I agree that a clutch type front LSD wouldn't be what I'd buy, but for the rear, in the S4, I would definitely do a clutch type LSD.

VonK :: Retired

Could you elaborate on the wheel spin issue?

whoizrob

I am running tracksports with the touring valving at 600/700. The car still wallows a bit more than I'd like, last car I had (240sx) cornered flat as can be but I realize nothing comes without compromise. This is a daily driver and I don't want huge spring rates to counteract the sway. I thought a sway bar would be a nice compromise which would allow me to keep my spring rates as is which is comfy but not sporty enough and then throw in some H-sports front and rear which should knock off a huge amount of sway and get the car rotating a bit better.

It just got me thinking about what that would mean for handling once you achieved turn in and were steady state mid corner and on exit. It also got me thinking what if such a sway bar package would be a bad mix with the rear and center diffs or could they be complimentary?

Rob

ryans4

with the S4, as it is stock, so:

Open front
2:1 Torsen Center
Open rear

to make this easy to follow where the power is going, imagine that you are moderately aclerating out of a turn. You are not acelerating enough (or lack the torque) to spin either front wheel. But since you are acelerating out of a turn, the weight shift is to the rear, and more torque is going to the rear.

Now, the Torsen doesn't know you have an Open rear differential. That open rear differential is going to send torque left or right, whichever is EASIER.

Now you take that same turn with the same moderate acceleration, but your massive rear sway bar has your inside wheel 6" off the ground. The Open rear differential is going to send all teh torque to the easier wheel to spin, which is the one in the air, almost zero resistance.

This aspect of the Quattro setup in a longitudinal engine configuration is solidified by the addition of EDL. If the system worked on a purely mechanical level, there would be no need for EDL to brake spinning wheels.

Fact is, adding EDL to a car with 5 channel ABS is much cheaper than putting a mechanical differential in the car.

Another way to look at a Torsen is that it is a Torque Multiplier. If you think of a lifted wheel as ZERO, anything times zero is zero.

The clutch type rear LSD is made to pick up wheel spin. So once that inside lifted wheel starts to spool up, the clutch type locks up and spins both wheels at the same rate. No wheel spin variance means no EDL.

That's how I understand it.

ryoung

The open rear differential always splits torque 50:50. If a wheel spins, it's HP that goes to the spinning wheel, and no power to the other.

ryans4

touche'

whoizrob

Don't those make a horrible clickingnoise at low speed corners? Who makes them? From my import days I know Phantom grip made something along those lines but they were poorly rearded as being a bad substitute for Quaiffes...

On the upshot they were cheaper =)

Rob