Re: Torsen Tech

[Brendan Rudack <rudack@umcc.umcc.umich.edu>]

Scott and others,

Here's  a summary of my experiences with Torsen cars:

The first scenario is a 90degree snowpacked corner. In the 90q I feel that
rotating the car with power is not an option (isn't enough) Therefore I
rely on wieght transfer and corner entry speeds to adjust the car attitude
and overall control.  As the corner approaches and vehicle speed is being
scrubbed off with braking (left foot) I find that a ideal turn is
accomplished when turn-in is made early(while modulating brakes with left
foot) and as soon as the tail starts rotating full throttle is necessarry
along with the appropriate amount of opp. lock.  The nose of the car would
then clip the apex followed by a drift to the outside of the exit of the
turn.  This can be and was accomplished succesfully many times by yours
truly.  However, the interesting part is the unnsuccesful attempts.
Scenario  one:

Entry speed too slow.
Car does not rotate  and begins to understeer wildly.  Attempts to correct
the situation.
(1)  Add full throttle and hope this induces oversteer.  
 Result:  Torsen senses decreased traction in front and sends power to the
rear.  Because, the trajectory of the car is more or less towards the
ditch (no slip angles) this poower application only causes the front tires
to "skitter" forward and plow the car off the road. (P-car 911 comes to
mind).

(2)  Massive yank of e-brake.

Result:  Oversteer is created, which must be "caught" by massive throttle
application.  This in turn   transfers more torque to rear end creating
more oversteer and a messy corner exitresults  but usually an avoidance of
the ditch takes place.  This is followed by several large
corrections.

Entry speed too high:

Assuming you rotated the car with left foot braking or at this speed an
abrupt lift of the throttle will do.  Problem: car is 90 degrees to apex
but on a tangent line for the ditch, back end first.
Attempts to correct situation:

(1)Lots of throttle.  Generally the result isn't good and the car stalls
from a tail pipe packed full of snow.... :-)

So, your probably saying that if the entry speed is correct, and the
correct amount of rotation is achieved than your set.  Unfortunately
making those judgements for every corner is difficult and if the
conditions are changing it is even more difficult.  The problem I see with
the Torsen is that when attempting to control the attitude of the car in
the corner using the throttle, it feels like a mess (As Scott says, "The
Torsen Hunt) . Therefore, it is
necessary to enter a corner in such a way that a constant throttle
opening(generally wide open in the gutless NA motors) is used to have a
nice corner exit.  Generally, this will get some proportion of front/rear
wheelspin  which seems to not confuse the Torsen, or should I say, not
make the Torsen do what it was designed for.

Now on a few occasions I have driven a '92 S4 IA? and I can say that the
car was sooo easy to rotate with the power, it felt much more controllable
to some extent.  Seeing that the car was not mine I did not push it very
much so I can't say much about the characteristics as described in
my 90q.  However, I have had experience driving 5ktq's on the track(dry)
and the tail is very controllable with the throttle, unlike my 90q... 
On the pavement, I have (admittingly) spun (180 in my book) the 90q twice
and just last week the A4tq. @ of these in the wet and one in the dry.
The car does not oversteer predictably when the tail slides out more than
a few degrees  when the traction is high.  The  predictability is the same
in the snow.  Tail out a few degrees a good dose of throttle will
generally bring it in, no throttle will keep it coming around (brother
Phil's mistake),  tail out a few more degrees  this same dose of throttle
will keep it hanging out(Scott's 70mph sideways 90q run, and my own
personal Colorado I70 scare!).  To attempt to summarize this,  the Torsen
cars have a limit at which their  predictability goes away which is lower
than an open dif Q. A Non-Torsen, open dif, quattro will just keep driving
predictably at the
limit, and maybe beyond....

The explanations to my observations are open to criticism... :-)

Brendan Rudack
'98 A4tq
Fenton, Michigan USA