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RE: Torsen Tech
well scott, your explanation seems to perfectly explain the cornering
posture with the centre diff locked as well as torsen....
lets have a look at this some more.
1) the torsen will *never* deliver 0% torque to an axle, but about 30%
minimum. by design. in this situation the locked centre diff of a
generation 1 quattro will deliver 50%. thats 20% difference. not a
hill of beans...
2) if you lift a wheel, both the torsen and locked centre deliver the
same results. zero torque to either the front or rear; or "axle" (ie.
all torque to the wheel without traction).
3) with the locked centre diff of the generation 1 system, you never get
*more* than 50% of the torque to an "axle", whereas a torsen car can
augment that by another 20%; meaning more traction in exiting a corner
(weight transfer to the rear).
to look at your analysis point by point. i'm assuming the generation 1
car has the centre locked...
1) entry to the corner. there is less understeer on the torsen cars
than the generation 1 cars because, under braking, the tyres adhesion is
being exceeded by the demands for braking meaning that the ability to
steer is affected. in the generation 1 car it is always going to be
transferring 50% torque to the front - overloading front-end grip
earlier than with the torsen where only 30% is being used. ipso facto,
less relative understeer with the torsen. this is a *good* thing, as it
raises the limit for understeer above that which the gen 1 car can
achieve. (higher limit means greater entry speed, or sharper turn-in or
both). the torsen can also modulate the conditon more than the
generation 1 car which will "plough on regardless".
2) oversteer through the corner (from apex). the oversteer condition
(rear grip exceeded) will result in a transfer of torque to the front,
but it's not "all-or-nothing" as you make out. with torsen, you are
always sending 30% to the other "axle", at the worst case, and it is
*not* a matter of "either 30% or 70% - as the torsen is quite happy at
50% or 45% etc. this means that you can modulate the car on the limit,
and set up nicely controlled 4-wheel drifts through a corner. btdt many
times with my cars. perfectly controllable, and safe and, btw, "on the
limit" by defnition.
3) when this tends to turn to brown smelly stuff is when a wheel is
lifted. in this case the torsen and generation 1 cars are very similar,
except that the gen 1 car will only lose 50% of it's torque, and the
torsen 70%. having said this you can drift a torsen car with the inside
front lifted and it seems to be nice and controlled. i've done this
with the rs2, not the ur-q btw. a generation 1 car without the centre
diff locked and you're geting 0% torque everywhere. you exit the scene
at high speed backwards through the nearest fence/hedge. you then find
the brown smelly stuff all over your seat...
above analysis is augmented by my own experience with my cars; gen 1 '85
ur-q, torsen ur-q and rs2. i have no experience of other torsen
>Date: Sun, 22 Feb 1998 17:40:39 EST
>Reading with interest Jeff Goggins extensive technical posts on the Torsen
>personality. Having explored the center Torsen phenomenon several times
>myself, and had some interesting off-line discussions with Jeff and Graydon
>regarding both at the track and off-road Torsen behavior, I want to add some
>specifics to his excellent explanations.
>Jeff touched on a couple of points that really hit what the torsen is
>"thinking" while one carves into a turn. Basically, the unit is sensing a
>slower rear wheel rotation on initial turn in, so more power is transmitted
>the rear axle, per Jeff's post. Let's explore that more fully to understand
>the handling of a Torsen at the limit thru a turn.
>Car: 1991 91 200tq, Stage II modded computer
>Turn: 90 right at the end of a long straight. Dry track.
>Enter the braking zone. Loading the cars' nose heavy front end, chassis
>dynamics will give intial understeer as you steer for the apex. So, Entry
>Strategy (as per most fwd): Late brake, oversteer before the apex, and drift
>out with power. Not quite.
>As you oversteer to correct the understeer inherent to the chassis, you add
>power to initiate drift. You now have the front wheels turning faster than
>the rears (like the speed skater on the inside vs outside of a turn), and the
>torsen "thinks" - Wheel slip in front, add torque to the rear. Well ok, now
>you have the wrong line for the understeer you initiated into the turn. Now
>the chassis is exibiting oversteer, your line is for understeer. What
>happens? The back end will go out fast. Your correction? Off throttle,
>steer for the apex again. Torsen: Back to front wheel understeer condition,
>oversteer again, add throttle, back end out. My definition of hunting torsen
>awd thru a turn. Happens on all the torsens, the smaller cars have a more
>control advantage, because the COG doesn't change as much as the larger and
>effectively softer sprung cars for a given turn, but it's still there. Those
>with less power have less of a problem, since WOT oversteer is hard in the
>dry, but those pups on a slick surface will have a bigger problem, since a
>short wheelbase car will do things quicker than the longer ones, including
>Next let's look at what happens beyond that oversteer, where you have the
>90 degrees+ to the apex of the turn, the "expert" line. Ok, so you've
>the turn, added throttle, back end comes out. One of two things will happen.
>A) in low traction, you keep your foot planted, and the torsen eventually
>will "find" that both axles are spinning at the same speed, and you have a
>50/50 split. OR B) You lost your balls and lift throttle. <A> is a better
>proposition, but takes some serious practice to get correctly. I saw a
>of posts (Jouko) that indicate that in an exercise this can be easily
>modulated. I argue for a given turn or exercise maybe so. For a full track
>or conditions which change, maybe not so.
>The difference between a race driver and one who "exercises" is repetition,
>exactly doing the same thing every lap of a race. Few do, specifically, the
>number that don't in the street world exceeds exponentially the number that
>do. On the track, Dave L experienced the "changing" condition issue, torsens
>at the limit can repeat, but as steamboat got more slick, the handling of the
>tosen did too. Why? Because the torsen will reach the equal torque split
>(50/50) at a different chassis to apex angle as conditions change. Where you
>found 50/50 at 90 degrees to the apex the first time, will be less as the
>traction lowers. Lift throttle doesn't help either.