Re: Torsens: shifting ground again...

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

>------------------------------ 
> 
>Date: Mon, 4 May 1998 15:36:15 EDT 
>From: QSHIPQ <QSHIPQ@aol.com> 

> [snip comments on misundersstanding vc's, see separate mail]

>>also as i have shown, the other 'ragged edge' scenario, inside 
>>wheel lift, is better with the torsen and vcd, than the locked centre as
>>more torque goes to the end where it is needed, while the unlocked centre
>>will 
>>be much worse because it has no bias ratio to limit the damage (this is the
>>famed genration 1 quattro spider bite, btdt).   

>Wait, slow down dave.  You are taking wheel lift, and appying it to a locked
>center and an open center.  "TIB" than an open center.  A locked center?
>Well, what is at the diffs, a torsen or a locker or an open?  With wheel lift,
>Trg to the ground is reduced in a vc, torsen or locker.  In an unlocked center
>100% of torque goes to the spinning wheel, it just costs more in tires  The
>net effect is the same, Trg to the ground is reduced, claiming one to be
>'better' is ignoring the effect of wheel lift on any of the diffs.  

no, 100% to the spinning wheel (aka open centre wheel lift) and what happens to
the vehicle?  loss of *all* drive.  think about that.  this means a big
oversteering moment (like a total throttle lift), without any ability to
correct with the throttle.  this effect is much worse than the other scenarios.

in the locked centre, you have have a bigger tshift to the rear than you do
with the torsen, with 100% of torque at the rear axle (with equal driveshaft
rotational speeds).  with the torsen, you have a tshift of 50% of torque to the
rear until 75% of torque (the bais ratio) is rearwards.

wheel down (after wheel lift):

the open centre applies all power back again (to the spinning car, now pointing
sidewards to the corner).  whooaaaa, want to guess what happens next?  try it
sometime.  i have btdt, sounds like jeff has too...

in the locked centre 50% tshift occurs to the front.

with the torsen, tshift to the front is 25%.  less tshift, better performance.

>
>>anyway, the point of this note is that i've been thinking about the slip
>>angle 
>>thing, and keep coming back to the importance of wheels/tyres and chassis
>>design to this equation. > 

>Not with you on this...  You are overloading the supercray again.  The
>variable is CF, not the tires relation to cf.  You stepped too far given the
>device.

ok, so you're saying that the tyre does not impact cf.  it does, of course, as
does the chassis loading on the tyre.  so, ipso facto, the quality of the
tryes, and more particularly, their behaviour at various slip angles are very
important.  doesn't the chassis have a fundamental affect of tyre load?  you
bet it does...

it all seems like chassis dynamics to me...

[snip]

>"Grip" and perception of it has nothing to do with driveshaft 'rotation' in
>regards to slip angle. "Dumb, &*$#! gear jamming friction device", isn't
>smart, by definition.   We could say for a given cf, a given tire has a given
>'grip'.  This 'grip' given cf affects the 'significance' chassis dynamics of
>slip angle.  You must identify the cf first. Given 4 tires of the same make
>and size, really not necessary. Making this too complicated Dave.  Driveshaft
>rotation and slip angle don't care what your 'grip' is.  The bite happens
>sooner or later.  Tires irrelevent.  You want to say :"At a high enough grip,
>no torque shift forward occurs".  Wrong.  Regardless of tire, you still have
>U-O-U in a turn in a audi 78/22/22/78 center torsen.   >

you misunderstand what i'm saying.  the coefficient of friction does *not*
change over the wide range of slip angle as supported by most tyres.  therefore
it's input to the "dumb" torsen is immaterial.  certainly up to 70% on a dry
road.

scott, you have been telling us all that the torsen gets confused with slip
angles, because it can't understand the difference between traction and slip. 
ok, i say, so what?  for the tyres you and i use, the coefficient of friction
provided by the tyre is the *same* over a wide range of slip angles.  therefore
it *makes no difference* to the operation of the torsen.  by definiton.  no
argument, at least to the point of the slip angle increasing to the point of 
*decreasing* cof. your argument (at least the 7/10ths on a dry road bit), does
*not* affect the torsen.

ref: carrol smiths book.

btw, the torsen is capable of locking 75/25 to 25/75, not 22/78, 78/22 as you
suggest.

[ major snippage, with the same comment above]

>Scott Justusson >

dave
'95 rs2 
'90 ur-q