Torsen II

[QSHIPQ@aol.com]

Dave Eaton writes:

>well scott, your explanation seems to perfectly explain the cornering
>posture with the centre diff locked as well as torsen....

Not exactly Dave.  I will follow you point by point.  A hunting differential
will give different corner characteristics AS you drive thru the turn.  A
locked differential will give you a constant "character" as you drive thru the
turn.  A torsen center behaves like an fwd car, I raced an fwd car in
ProRally, and drive the torsens that way too.  There is an EXACT reason why no
race cars (period) use a torsen center.  A question to ask your mentor (and my
hero) Herr Rorhl next time you speak...  One needs to wonder why all the race
cars use a fixed diff split, in fact, audi used them (Walter included), tho
somewhat varied the fix to conditions (60/40 to 70/30) in all their races as
well.

...

>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...

Disagree.  That 20% is the more than the TOTAL variance audi and WRC put into
the race cars different center diff torque settings (see above).  For 7/10ths
driving, I have no problem with the above, over that, it means a mountain of
beans.  PREDICTING a cars handling is part of a driver understanding chassis
dynamics.  Predicting a differential that by design can and will hunt from
75/25 to 25/75 without driver control is hoping more than predicting.  Unless
of course you have the proper line, and your foot to the floor.  More power to
you (literally as well). Good luck.

>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).

See rear locking comments.  No disagreement here, by design of both.  I have
argued for a trigger locking switch for the rear for this exact phenomenon.
Also a reason, I suppose, that audis rally cars don't use swaybars front or
rear.

>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).

Assuming your line to be correct.  I look at <2> and <3> and immediately
think, chassis setup is key.  All wheels on the ground with both systems is
best.  Not convinced you "use" that extra 20% either.  Sending "up to" 20%
more torque (not traction) to the rear of a cornering car you see as a good
thing, I don't necessarily.

>...

>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. 
I don't go here with ya sir.  Loading the front end of a front heavy car gives
understeer, a chassis and suspension issue.  I find torsens and non torsens
understeer, they both do.  More or less?  Tire pressure, driver weight, fuel
weight, shock condition, camber, caster...  A plethora of these variables make
more difference than your reference above.

> 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".

UP TO 30% might be my response.  I don't follow the rest of the presentation
Dave.  A torsen car under WOT gives oversteer at a point, it varies, and those
of us that don't have the RS2 to make that point at a lower chassis to apex
angle, are "hanging" out waiting for your argument.  Hanging way out, in fact.
Your last sentence to me is 180 off.  Torsens modulate, in spite of the driver
input.  They are dumb.  They ONLY sense one driveshaft spinning faster than
another, WHATEVER your helmet and feet are deciding to do to the cars
attitude, I presume even under the best of helmets, that to be a variable.
Non torsens make understeer a constant, now the driver gets to control more of
the chassis dynamics.  

>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.

>From 75% to 25%, and everywhere in between.  Ok, try it without the turbo car.
I argue that you are controlling your slip with power, which to me is the same
as a lower traction cf.  So, in effective terms, you hare reduced the chassis
to apex angle you need to make a "controlled 4 wheel drift".  Understand where
I disagreee Dave.  "Always sending" is an UP TO argument, NOT a constant
argument, by the design of the torsen differential.  Getting all this right is
NOT an easy task.  Can it be done?  Sure.  I argue however, I have not been in
the car (and I go to most of the QClub track events as an Instructor) that has
mastered it, time after time.  Getting a locker to repeat is easy in
comparison.  When the torsen bites you, it chomps.  I've seen it with some of
the best drivers.  You have the advantage of power that helps you with
control.  I argue that you find that 75% power right away and stay there or
close thru the turn, the proper line.  What, I wonder would the difference be
if you had a diff that was always at 75%, or even a little less, like 65/35.
Given the "hunt" by design I argue you would be faster.  So does every awd
race car team.

>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...

Seems to be, is that seemless torsen spider hypnotizing you...  UP TO 70%, not
a constant.  When the brown stuff is imminent, I sure don't want some Torsen
gizmo, trying to help me get my ass out of a sling, at 11/10ths I'd like the
constant in that center diff thank you.  I've been at 12/10ths with both a
torsen and a non.  That UP TO hunt, takes a lot out of your nerves before you
get back to 10/10ths, btdt.  Both require WOT to get anything done.  But I can
tell you the hunt makes time stand still in the torsen, not a comforting
feeling at any speed.  

I appreciate your input Dave.  And would enjoy that torsen ride someday with
you.  From a physics standpoint however, I'm not sure that a variable center
diff is better than a locker.  Given my druthers, I would go for a fixed 65/35
or 60/40 r/f split, but happy to take 50/50 for the sake of a constant.
Adding more HP can make up for that up to 20% you argue I may be missing 

>>>...i have no experience of other torsen cars....

I would love to see a post after you drive one of the more "hp challenged"
cars with a torsen, Dave.  You might better understand my points.

Darn RS2 drivers....  :)

Scott Justusson
QSHIPQ@aol.com