Re: TORSEN CENTER - OPEN FRONT!!

[Dave Eaton <dave.eaton@minedu.govt.nz>]

ok, since you've got it all figured out, then explain to this moron what the
difference in your "nightmare" scenario is to the type 44 with the locked
centre.  i mean, you're got it all figured out haven't you?

ok, here we go, now pay attention here!!!!

you overcook the corner (much more likely because you've got no abs due to the
locked centre diff, and it's wet, we'll you're a good driver so you'll cadence
brake i guess)...

you apply the gas, and load up the front.  yipee, we've got an open front diff.
 it's open open open, and what does the little sucker do?  well, you know that
the weight has transfered to the back and so the inside front wheel is a little
light, and well, you know what happens.  bingo! spider bite!!!!!!!!!

you're suddently without 50% of torque to the front, bang, big oversteer
moment, that is until the inside front regains traction and then bingo, 50% of
the torque to the front axle again.  in the torsen scenario, there is only 

************ 30% *************

power loss, with the locked centre diff (generation 1) diff there is 

************* 50% *************

so what so bloody great about that? guess which one i prefer (need a hint?).
you get the picture now? so can you tell me whats so great about the locked
centre now?

i assure the above is repeatable, any time....

oh, and try the above in the wet without the centre diff locked (as a majority
of generation 1 audi quattro drivers will do at some point) too hot into the
corner and it turns out to be wet, oops haven't locked the centre....  this is
more than spider bite we're talking about here, it's backwards through the
hedge stuff.  brown and smelly stuff all over the inside of the car...

so, if the above is spider bite, by your definition, then the same thing
happens, except *worse*  with the generation 1 car with the locked centre diff.
 and you have no abs so your hot braking, and turn-in under braking is all to
hell anyway.

all in all, makes me wonder why audi didn't persevere with it :-)

the torsen is a damn sight better at making decisions about traction than you
are, it is a closed loop system.  when there is traction, within the limits of
the chassis, it will find it.

now, to your "data points"

..>I CAN'T HELP MYSELF ANY LONGER. So here goes.
..>
..>I've already stated this example, but it was never fully comprehended by
..>many. I will be as brief as possible.
..>
..>Conditions: Rain soaked track
..>Corner: Abrupt 90 degree 2nd gear turn
..>Car: type 44 chassis, turbo motor, Torsen center diff, open front diff,
..>open (but lockable) rear diff.
..>
..>Do the following (HERE IS YOUR REPEATABLE TEST).
..>
..>Go hot into the corner, don't hit the brakes until you begin turn-in.
..>This will set-up mild trail-braking oversteer. The rear wheels are now
..>rotating less RPM's than the front. Reach apex, apply full-throttle.
..>
..>PAY ATTENTION HERE !!!
..>Just before you applied full throttle, the rears were turning slower
..>(b/c of the slide), thereby *fooling* the Torsen (upon power
..>application) into ERRONEOUSLY deciding the rear wheels had more traction
..>than the fronts.
..>
..>Now the rears get a greater share of the torque (as much as 70%). They
..>quickly accelerate and cause further oversteer. Yee-ha!
..>
..>Torsen realizes it's MISTAKE only after the rears have lost longitudinal
..>traction (and outpaced the front) and a comensurate amount of lateral
..>traction.

nope, this is the behavour of a viscous diff.  you should read (and understand)
the gleeson article. to quote:-

"the bias characteristic of the torsen *instantly* reacts to unequal traction
conditions by delivering an increased amount of torque to the drive [shaft]
having better traction *before* the other drive shaft exceeds the limit of
traction available to it" (page 4).

..>
..>At this point Torsen says 'whoops' to itself and sends the FRONT OPEN
..>DIFF the Lion's share of the torque. Since you are accelerating, the
..>front wheels have less relative weight over them vs. the rear. You are
..>still cornering, so the outside front suspension is max'ed out, fully
..>loaded. THE INSIDE FRONT HAS THE *LEAST* TRACTION OF ALL FOUR WHEELS AT
..>THIS POINT. YET BECUASE THE FRONT DIFF IS OPEN OPEN OPEN, IT SENDS THE
..>VAST MAJORITY OF TORQUE TO THAT INSIDE FRONT WHEEL.

in the normal torsen operation this would be 30% of the total torque (because
traction has been lost the torsen has *already* sent power to the rear axle
(70%).  in the locked centre diff application this is 50%.  the effect is
*worse* with a locked centre.  still following?

..>
..>So you have the inside front wheel all lit up and are back in UNDERSTEER
..>MODE, though you had NOTHING to do with that change. You were
..>oversteering controllably, the next second TORSEN SENDS UP TO 70% OF THE
..>POWER TO THE INSIDE FRONT WHEEL!!!! THE ONE WITH THE LEAST TRACTION.
..>WHAT IS SO DARNED GREAT ABOUT THAT?!?!?

it will not do this.  ever.  the wheel with the least traction will only *ever*
get 30% power.  worst case.  with the locked centre diff, this is 50%.  it's
worse.  a worse spider bite.

..>
..> Tell me where I'm so completely mistaken, LINE BY LINE. I'LL GIVE YOU A
..>HINT - I'M *NOT*!!! NOR IS SCOTT OR JEFF. NONE OF US IS IMAGINING THIS!
..>IT IS REAL!!
..>

bollocks.

..>Torsen doesn't hunt all the time (perceptibly), and it doesn't manifest
..>itself in evil ways, EXCEPT IN THE RIGHT CONDITIONS. DO THE ABOVE TEST
..>AND YOU WILL EXPERIENCE THE TORSEN ACHILLE'S HEEL. I can make it happen
..>over and over again. I spent many laps in the rain at Thunderhill on the
..>above-described corner in an attempt to generate prolonged, controlled
..>oversteer. Not because it's the fastest way around the track, but b/c
..>it's a critical skill to have in your bag of car-control tricks. The
..>conclusion of my 'research': Torsen center diff plus open front diff
..>precludes prolonged, controlled throttle-induced oversteer in the rain
..>on that 2nd to 3rd gear corner in  a made for USA 91 200q TAP.
..>

[snip]

..>
..>Dave wrote:
..>>scott: you have not explained how a torsen can transfer 70% of torque
..>to one
..>>axle and then switch the same to the other axle in the same turn.  you
..>>misunderstand that the torsen is *designed* to only transfer *enough*
..>torque
..>>(within the bias ratio) to ensure torque equilibrium.  it is not an
..>>all-or-nothing device.
..>
..>Yes, he has. You just haven't understood him. He's laboriously explained
..>it, much more patiently than I, at least a dozen times now. Torsen sends
..>more power to the diff that spins slowest. Given OPEN front and rear
..>diffs, Torsen is free to make fallous conclusions as to which set of
..>wheels has more traction. EXPLAIN TO ME WHY THE OPEN FRONT DIFF IS
..>IRRELEVANT. Again, not only is it relavent, it is CONTROLLING!. By

[snip]

..>mechanical operation of the torsen IN THE LEAST.  Who you talk to and
..>who you attend track safety seminars with has NOTHING NADA ZIPPO ZILCH
..>to do with the mechanical explanation of the undesirable effects of
..>torsen center with an open front diff as described above.
..>

really, tell that to walter rorhl...

..>By request, I have given an infinitely repeatable TEST MODEL; So tell us
..>all how this whole 'bitten' thing is so implausible. Think hard. Read it
..>CAREFULLY.

yeah right...

..>
..>Regards,
..>
..>Sarge
..>

btw, another data point, i have spun up the inside front wheel in the wet in
the rs2 on numerous occasions, on a corner/onramp on the way home.  i know the
corner well, and found the rs2, with the inside front lit up, to be perfectly
controllable (for the reasons explained below), and a real blast.  but you've
got to get it right.  i've also understeered through the corner like a pratt
when i get it wrong in the wet...

know your car, know the conditions, know yourself.

dave
'95 rs2
'90 ur-q