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TSD's, what's with Trg

If you look on Page 7 of the technical paper found at:


We can look at a torsen used in a variety of chassis in terms of the Bias
Ratio (the amount of torque the slower wheel/Driveshaft can generate in
relation to the faster spinning wheel/driveshaft.  I would argue, as you
reduce Trg (total amount of engine torque) you reduce the likelyhood of the
"unlikely" (see page 10), UNLESS the cf of your road diminishes greatly, and
slip angle (rear) becomes high enough.  That is to say, a 150hp car will
transfer less total torque than Dave E.'s 300hp car.  Here's the math (very
carefully now, scotty:).

Assuming dry road, full contact, slip angle only Trg for a 160 ft/lb car vs a
300 ft/lb car.  

160 ft/lb, 75/25/25/75 torsen Center

T1/T2 = 3:1
T1 = 120
T2 = 40
T1 = 40
T2 = 120
Tshift = 80 lb/ft

What does that mean here.  Well that means up to 3 times the torque of the
faster Driveshaft can be generated in the slower one.  Assuming a dry track
that is a "transfer" of 80lb/ft of torque to the opposite driveshaft.  Not
astounding.  KISS, means that 120 ft/lbs can be at the front or the rear, 40
will always be generated to the opposing driveshaft.

However, take a ride in Dave E.'s car the transfer becomes more significant.  
T1/T2 = 3:1  Torque = 300lb/ft  
T1 = 225 
T2 = 75
Tshift = 150lb/ft
Wow, that's almost the total Engine torque of the above example.  For racing
sake let's double that again, probably the high end of audis racing efforts to

A full race spec audi with the same torsen.
T1/T2 = 3:1  Torque = 600lb/ft
T1 = 450
T2 = 150
Tshift = 300lb/ft
Yikes sakes, batman.  

So, given a set torsen (all gen II and gen II audis are 75/25/25/75) split,
the T-shift is insignificant as the traction cf is high and the HP low.  But
start messing with the higher HP/torque cars, "a handful" would be an
understatement.  However, the spider can bite just as hard if you take the cf
(page 3) and lower it.  Then even that insignificant 80lb/ft becomes a whole
lot.  Don't think so?  Think of this a little further.

The above assumes that you have ideal traction, i.e. no other factors
affecting torque.  But remember BR is figured in terms of traction/torque to
the faster spinning wheel/driveshaft.  So that means the 80 lb/ft of torque
shift is actually LESS with a lower cf of the wheel to the ground.  (Example:
A spinning wheel on snow in the 160hp car can puts down 20lb/ft of torque,
then the opposing wheel can only put down 3:1 times that or a 60lb/ft

So, as cf decreases, so does the Tshift, but as you decrease that cf, Tshift
becomes a more significant factor in potential for bite.  So, indeed we can
see that one can get bitten regardless of power, it's a cf issue as well.  A
turbo car has a higher potential for Tshift with a higher cf, but all audi
center diffs have the Tshift issue to deal with.

Plottable?  Not sure.   Might be interesting to look at.

Scott Justusson
'87 5ktqwRS2
'86 5ktqw
'84 Urq