Re: Torsen Tech II

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

scott is saying that the torsen will hunt without wheel lift (ie. loss of
traction on one side of the [virtual] axle).  or in other words that a relative
difference in driveshaft rotational speeds will produce hunt.

i say not, and that i've never experienced it.

we agree that wheel lift will produce similar results in non-torsen and torsen
applications as long as the non-torsen centre diff is locked.

lets clarify this some more....

1) entry to the corner you are talking engine braking and not power.  no
'hunting' by definition.

2) power through the corner is the only time 'hunt' can occur, and then only
when the torsen thinks that the relative traction available to either [virtual]
axle is different enough to change the torque bias.

the issue then becomes what level of relative axle rotational speed will
produce this effect...

i say that in normal cornering this will never occur.  that is, if you get the
corner right.  if you get the corner wrong (either under or oversteer), the
question then becomes whether the actions of the torsen in trying to get you
through the corner are benefitial or not.  in a severe enough (term to be
defined) under or over-steering moment, the torsen will detect the relative
loss of traction and send more (term to be defined) torque to the axle which
has the most grip.  this has the effect of restoring the cornering posture of
the car (read pulling an oversteering car through the corner or pushing an
understeering car into the corner).

so the issue to me seems to be about the thresholds of which we speak.  the way
you discuss it, scott, is a bit sensational (spider, bite etc).

setup an torsen ur-quattro and do your hot circuits and compare to your
non-torsen ur-quattro, and that's apples-for-apples.  otherwise not...

i repeat that i have not experienced this sort of bite, even when i get it
wrong.  in my experience the torsen particularly helps in the oversteering
situation where it is quite easy to get a 4-wheel power-drift going.  it is not
helpful in the understeering situation where you've basically carrying too much
speed and your line is wrong.  nothing much helps here except to get off the
power (no centre diff action by definition at this point) and try and recover
your slip angles.  when your angles are better, back on the power and the
torsen will distribute it where the most good occurs.

another data point is that the ur-q torsen understeers a *lot* less than the
gen 1 non-torsen cars.  this helps cornering heaps.  my 20v certainly
understeers, but a lot less than my non torsen ur-q [with locked centre] did.

now i've driven the ur-q over a timed circuit course with walter [big cojones]
rohrl as my passenger/driving instructor.  in the debrief (after his hot laps
in my car), he pointed our 2 things: smoothness at particular points and the
line under braking.  the course included a slalom, 90 degree apexes, haripins
and put an enphasis on carrying speed through the circuit.  i made no mistakes
and my time wasn't too shabby next to walters (+3 secs).  earlier in the day
(an in an a6), i had placed 2nd over the same course with a group of 30 which
included 2 former national saloon car champs.  anyway point is that the ur-q in
my hands and walters was dynamite.  absolutely bloody fantastic.  ear to ear
grin. no dramas, no nappies.

the wheel lift scenario is basically getting it all wrong.  to hot in, off the
gas, oversteer, inside front lifts, then the fun starts.  put my old 10v ur-q
on it's lid in a field.

anyone got some information on the relative rotational difference int he axles
whcih is required for the torsen to act?  graydon?

dave
'95 rs2
'90 ur-q