RE: Bites of dead horses, last post for me

["Dave Eaton" <Dave.Eaton@clear.net.nz>]

bingo scott, you've got it.  same torsen, different chassis.  some affected,
others not.  as the zexel paper states.  let me see, spring rates on the
type 44 vs the type 85?  weight distribution?  torsional stiffness?
suspension kinematics?  all different and will never be the same.  all
stated as important by zexel.  hence you have to accept that the bite will
never happen on some chassis where it can happen on another.

i also find it interesting that the engineers who modelled the torsen
required 6 different variables in order to model it's operation (torque,
weight, f/r weight distribution, roll, suspension stiffness, tbr) - most of
the variables obviously *external* to the device, but obviously contributing
to it's operation.  they believe that any less than those 6 degrees of
freedom leads to an incomplete understanding of the device.  needless to say
these factors are all different between the type 85 and the type 44.

as phil has found in practice.  possible bite on the type 44, no bite on the
type 85.

happy to point you in the direction if you want to have a look at their
maths...

perhaps audi decided that the type 44 would not be used in the same way as
the type 85?

also, your preoccupation with torque shift is a little difficult for this
lister to understand when you favourite locked centre diff will shift torque
up to 100% (not 56% as the torsen can).  perhaps you should re-think your
maths for this case?

as for the handling of the sport quattro (with locked centre).  what do you
think contributed to it's twitchiness?  perhaps we should say that because
the sport q was very twitchy with a locked centre, all quattro's with a
locked centre's are twitchy?

dave
'95 rs2
'90 ur-q
'88 mb 2.3-16

-----Original Message-----

Date: Tue, 21 Sep 1999 22:02:16 EDT
From: QSHIPQ@aol.com
Subject: RE:  Bites of dead horses, last post for me

Dave E writes:
>errr, au contraire scott, there is considerable documentation which
directly
>contradicts your view, from a variety of sources.  for example:

Uh, oh.  But I don't disagree with the below, just draw a different and
blatently obvious (IMO) conclusion on what was written:

>i have a white paper from zexel which specifically mentions a range of
>chassis factors in the behaviour of the diff.  let me quote:
>"The ideal centre differential Torque Bias Ratio layout in the 4 operating
>modes is a function of vehicle dimensions (wheel base, track width, centre
>of gravity height, etc.), suspension elasto-kinematic design (stiffness
>front/rear, angular variations, etc) and engine torque characteristics for
>given road conditions.  Therefore the ideal design characteristics for a
>centre differential can be determined after a great deal of subjective
>vehicle tests.  The optimisation will be a compromise between different
>set-ups, depending on the surface conditions (dry asphalt, wet asphalt,
>snow, ice, etc)."i think that the text makes it pretty clear, don't you?

Absolutely positively clear Dave.  Reread:  "IDEAL"  Problem:  a) what is
"given road conditions"?  What exaclty is the "optimization will be a
compromise" mean in terms of u-o-u vs straight line traction?  and 2) if
exactly the same torque split is used (the same device) which chassis are
compromised and which aren't, in the audi lineup.  The above are the factors
that affect the when, not the IF of inappropriate torque shift by the
device.
 Bottom line:  Compromises HAVE to be made to the device, cuz it can't
perform optimally in all.  That's what the above says, always has.  Help?

>i also have a white paper from the boys at gmc who developed a mathematical
>model for the torsen with 6 (count 'em thats six) degrees of freedom.
>in your model scott, you've got 1 degree of freedom (i.e. if there's a
>torsen, there a bite).

Nature of the device, sorry, not my device, only my evaluation of it.  And
Stan Chocholek's.  Not much freedom to play in a torsen car, sorry btdt.

>enough said.  as for your previous attempt to recreate history by stating
>that phil or myself had categorically denied the possibility of ill-defined
>chassis behaviour with the type 44 at the limit, i am endeavouring to take
a
>charitable view....

If it happens in 1, the conditions only have to be right with the other
chassis (reread your first paragraph).  You both denied it happens in some
of
the other chassis.  Hard case to make.  Think about it, if 56% of torque
shifts in one chassis with the right matrix and the device is the same, it
shifts that in every chassis with the right matrix.  You can't single one
out, a device fooled is fooled.  I'm amazed that 78%front to 78% rear engine
torque is controllable by any driver in ANY chassis, especially considering
Blomqvists own comments below.