RE: Torsen tech

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

scott, drive your new bmw rwd and you will find understeer most of the time,
despite 100% rear torque bias.  likewise it is perfectly possible to have
oversteer with 75% torque at the front of a torsen or locker quattro.  100%
torque to the front of a fwd car and you can have oversteer (btdt on all of
the above).

these statements you make about 75% torque front meaning understeer and 75%
torque rear meaning oversteer are so prone to error and misinterpretation as
to be totally meaningless.

with regards to your claim of the bite being referenced in the 885140 paper,
i am still at a complete loss to find this reference.  however,

you say that "the turning radius fools the torsen into allocating more
torque rearwards... overloading the rear tractive ability".

you are correct in that if the torsen is in a turn, it will allocate more
torque rearwards.  as will the locker.  by design.

given the torsen is not at the bias ratio, it is not allowing output shaft
speed differences.  to clear up your misunderstanding, the paper says when
measuring the dynamics of a 80q in a turn that "0.2% of forced slip occurs
between the 2 axles which reduces the slip under traction at the front
wheels and increases the slip at the rear wheels.  this results in tractive
forces being redistributed towards the rear wheels".

scott, this means that the *tyres* compensate for this slip *not* the axles
speeds.  you misunderstand this.  the torsen at this point (before the bias
ratio) has locked the output shaft speeds.  it is operating as a locked
differential would.  hence any "claim" you make for the torsen at this
point, you have to also make for the locker.

btw, the torsen will not allow any axle to "spin up" until it is at the bias
ratio.  this is a function of torque inputs or tractive forces at the tyres
or both.

i really don't know how i can make this any clearer...

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

Date: Tue, 2 Nov 1999 10:19:19 EST
From: QSHIPQ@aol.com
Subject: RE:  Torsen tech

Dave E writes on 75r/25f as O and 50f/50r>75f/25r is U:
>no of course it isn't.  just as it isn't a fair statement to say that 25:75
>torque in a locker is oversteer.  anymore than it is fair to say that 0:100
>torque to the rear in a bmw (by definition) is oversteer.  it isn't,
because
>in the chassis, it's mostly understeer.

So, we can't change any variable in 885140 to create O with less than or =to
75r/25f? According to Scott Fisher, tire loading affects slip angles.
Doesn't that mean indeed a torsen *can* oversteer at 75r/25f?  What does
"...because in the chassis, it's mostly understeer" mean?  I interpret
"mostly" to mean that it *can* be oversteer.  Yes?  Under what dynamic
conditions *can* that be, Dave?

>Definition of Spider Bite (as I understand the device, based on my research
and >Dave E's):
>Torsen center diff car enters a given turn, turning radius fools torsen
into
allocating >torque rearward -O-, which (depending on all the variables in
885140) *can* overload >the rear tractive ability, which then changes the
variable affecting torque shift from a >slip angle one (turning radius) to a
tractive variable (traction at the rear wheels), >which per 885140, is
"independent of the forced slip resulting from the vehicles >circular path",
and this shifts torque forward, causing -U-. which then *can* regain
>tractive force rear, which results in -O-, because once tractive force rear
is regained, >torque shifts rearward due to turning radius.  This scenario
*can* cycle several times >in a single turn.