[V8] Making an A8 ride like a stock V8

[DasWolfen at aol.com]

In a message dated 2/18/05 9:19:17 PM Eastern Standard Time, 
Steven.Buchholz at kla-tencor.com writes:

> Basically, what happens is that the Torsen tries to shift power away
> from spinning wheels, which is what happens when the rear end starts to
> come around.  The Torsen will start to drive torque toward the front
> wheels, which can make the rears hook up and the fronts come loose.  I
> find that I need to plan on backing out the steering correction for the
> slide earlier than I would on my cars with the open center diffs to
> prevent having the car go the other way.  This is the situation referred
> to as the "spider bite" ... 
> 
> The one thing that is unfortunate about the center Torsen IMO is that in
> any turn, the fact that the rear wheels describe a larger arc than the

> fronts will cause the Torsen to bias toward the front wheels even when
> there is no slip.  This same effect occurs on the rear Torsen ... the
> fact that the outside wheel goes farther causes the Torsen to feed more
> torque to the inside wheel.  

 A great description Steve!  

 To drive an AWD car hard in the corners you treat it like a FWD car on 
entry.....because both drivetrains dont like to turn under power.....Its late hard 
brake and early apex to get the car through as much of a direction change as 
possible early.

 The difference is an AWD car should be able to power through from this point 
since it has 4 wheels to take the torque.  Unfortunately the center torsen of 
all the later manual quattro's ruin this by torque shifting to the front 
preventing optimal torque split. Even this wouldn't be so bad except the torque 
split CHANGES while you're in the middle of the turn! making the car act like a 
FWD that has suddenly started spinning the front tires...instant dramatic 
understeer. Think about it, if you're driving hard enough to force oversteer and 
suddenly find yourself with unexpected understeer.....you might be in for a 
real scary ride.

 Several Audi "toys" are set up using early locker tranny's and the V8's 
torsen rear diff....effectively recreating the diff alignment of the auto 
V8......open front, locker center, torsen rear.  By all accounts everyone who has 
driven these cars on track report exactly the same thing.....incredibly stable 
oversteer possible almost at will.

 It might seem odd but the torque shift from side to side in the rear 
probably aids the handling. By applying more torque to the inside wheel it overloads 
the traction of that tire with the result that the already heavily loaded 
outside tire now has to carry even more of the cornering force....causing it to be 
more likely to break away...allowing  the power on oversteer you want in a 
tight turn.