Torsen Test Redux w/ 88 80q

Dave Eaton Dave.Eaton at
Wed Jan 23 10:54:46 EST 2002

sorry to contradict listers here, but in the scenario noted (i..e *zero*
traction at the front, with a torsen 1 system), the car will not move.

the pricinple of the torsen (often misunderstood on this list), is that it
allocates torque *across* the unit. i.e. it will allow approx 3x the torque
to move to the end of the diff with the most traction *from* the end with
the least (i.e. that is the *input* torque to the system), leaving the
remainder for the end with the least traction.  if the torque isn’t there in
the 1st place (as in this case), the torsen has little torque to allocate.
in the case where one end has zero traction (i.e. it is in the air), then
effectively little or no torque goes to the other end.

in the later quattro systems, edl takes car of this by using the individual
disc brakes to the spinning wheels (within the control parameters of the

in the earlier non-torsen systems you have a similar difficulty.  with the
centre diff unlocked, you have the *same* torque allocated to each end of
the car all the time (with a similar result as noted above, as the torque
from the front is zero, so the torque to the rear is zero, so the car will
not move).  with the centre locked you have no control over the way in which
torque is allocated, and up to 100% will go to the end of the car with
traction.  in the scenario you talk about, with zero front traction, locking
the centre diff will move you forward.

bear in mind, that short of having the front end in the air, zero traction
never occurs, even on ice, so the torsen still works quite effectively.

effectively this means that with a torsen 1 system, you can jack the car up
so that 1 wheel is in the air and the car *may* be able to drive off the
jack, but not if you push against it (i.e. little torque available, so (3x)
little get to the wheels on the ground).  with the unlocked centre diff, you
could not drive the car off the jack.  with the centre diff, this little
experiment would be a dumb idea

’95 rs2
’90 ur-q

-----Original Message-----
From: bludodger at
Subject: Torsen Test Redux w/ 88 80q
Date: Tue, 22 Jan 2002 06:12:04 +0000

I read the archives on this but thought I should ask my
question to our present day it goes:

'88 80q- both front wheels on sheet of pure ice (read-no
friction). Both rear wheels on dry ground. Rear Diff.
unlocked. Car started up and put in gear and accelerator
pressed. What should happen in theory? Does the car move
forward? Do the front wheels just spin on ice? What
happens when rear diff. is engaged (locked)?

Just curious and a bit confused with the torsen system
of my car.

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