Spider bites, those who have vs those who will

[QSHIPQ@aol.com]

Dave writes:

>1) non-torsen cars understeer more because they are unable to deliver
>any *less* than 50% of torque to the front which overloads the wheels
>already struggling to cope with cornering and braking.  not a good
>thing.
Both cars understeer.  Both understeer a lot, on turn in.  Once you apply the
power to a torsen car, that initial understeer BECOMES oversteer.  So let's go
thru both cars.  

Torsen:
Initial turn in:  Understeer
WOT turn:  Oversteer
Lift throttle:  Oversteer or maybe understeer, depends on where you are with
the car and the torsen.  If you are in WOT oversteer (on line, torsen rear
biased) you will Lift throttle oversteer, and spin.  If you are modulating
(wrong line, torsen hunting) you will understeer.  Why?  Cuz the torsen with
anything less than x/x (insert number) rear biased WOT line, will understeer.

Non Torsen Locked center diff:  
Initial turn in:  Understeer
WOT turn:  Understeer
Lift Throttle:  Understeer

>2) both torsen and non-torsen stuggle when a wheel is lifted.

Lock the rear on a non torsen, not a problem.  Given the chassis and spring
rates we are talking about here, I don't see this as a real issue.  I've run
some pretty high spring rates on audi awd cars (like 400+) and don't get wheel
lift.  I would argue that wheel lift is a suspension problem, not a torsen or
non torsen one.  But your statement is correct.  Other than factory race cars,
how many pix do you see of a quattro on 3 wheels or less.

>3) a torsen "hunting" only happens when traction gets lost.  see point
>(2) above.

INCORRECT dave.  A torsen hunts with a change in relative driveshaft speed.
That's all.  That doesn't necessarily require loss of traction for that to
happen. The difference in front and rear track or slip angle is enough, so is
throttle position.  You say it yourself with the WOT line is the only way to
go, power slide out.  Why?  Cuz if you don't, that torsen hunt becomes a
handful few can recover from. Wholy looking at point <2> above, I see you
equating this with wheel lift.  The hunting torsen doesn't need wheel lift to
bite.  Just momentary throttle lift is enough.  

>4) most of the manouevers of which we speak are done with power on.
>certainly if you are attempting to power slide a ur-q or rs2 by
>modulating the power, you'd better be wearing nappies.

Fine for the track, a controlled condition.  What happens on the street when
the deer suddenly jumps into your power sliding corner.  Late brake, power on,
oversteer slide out to the exit.  Sounds really good to me.  In theory.  Go
too hot into that corner what do you do?  Lift?  Accelerate?  I don't feel
comfy sitting in the passengers seat offering up either advice on a torsen
car.  My advice:  Don't go too hot into that corner.  

>in my experience, i have had the rs2/ur-q and my old s2 understeering
>through a corner (too high entry speed, too much mower too soon), and
>have had an oversteering twitch on entry to a corner (brakes).  but
>usually, i'm hard on the power through the corner and the car is flat
>and fast.  big grin factor.  no nappies.

Then, I argue, that you have the line, and a rear biased center diff all the
way thru that turn and/or you haven't been over it.  So you haven't been
bitten yet.  I have, so have many others, some who have buried their toys
because of that bite.  It's a torsen spider bite, by the very mechanics of the
Torsen, you can't control what the hunt will be unless you have WOT oversteer
on line.  Cross it sometime and try to bring it back, dave.  That's where I
put little confidence in those spider gears.  Make sure you have a really big
out, please.

>...
>wrc rally cars are all using active centre diffs and have been for a
>couple of years.  ditto the old fia class 1 super cars.  an active diff
>is (by definition) going to change the torque distribution
>characteristics of the car through the cars cornering manouevers.  is it
>quicker?  you bet.

Well maybe we could explore the difference between active and a torsen.  I
don't put them in the same group, I put them closer to the fixed diffs with a
very limited range of change, so the crew doesn't have to put in a different
center diff for each race or venue.  What are the f/r ratios used in those
active cars?  75/25 to 25/75?  I argue not even close to that range.  

I don't advocate that torsen is a bad thing necessarily.  Only that it has
it's limits, beyond that a whole raft of crazy s**t happens, and really
quickly.  Or, more specifically, as you went beyond, and you want to come
back, a whole lot of time has passed, more than you may have available.  Gen I
has it's limits too, however beyond them is a very safe predictable and
reasonable place to play.  With only understeer or more understeer the
variable in that center diff.   Driving a Gen I at 10/10ths+ is a relatively
easy task.  Driving a Torsen at 10/10ths+ has a lot of brown stained leather
associated with it.  I advise not to get bitten, it ain't fun.  What you get
is a lot of respect for exactly what a Torsen isn't.  Predictable.  When you
are at the point of the bite, the last thing you want to happen, is have a
hunting differential tripping up your technical and delicate q-dance.

Food for thought from one with many spider bite memories.

Scott Justusson
QSHIPQ@aol.com