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Spiders on the web (long)
Rereading Sarge's post might is the bite I've tried to explain here. Maybe
looking hard at Sarge's post in terms of the torsen and the chassis might help
make this more clear.
As you enter the turn, and you add power what exactly is happening? The slip
angle of the rears is more than the front, and the fronts are taking a faster
line around the apex than the rears (track). This combination means the rear
axle spins slower than the front. Why? Because the front tires can be
steered, and assuming you to do that towards the direction of travel, their
slip angle will be always less than the rears. So what does the torsen think
about all this?
In terms of it's function it doesn't care what you are doing. In terms of
physics, the slower rear axle will be sent more torque. Why? Because if the
rears are slipping more than the fronts (in terms of slower forward rotation),
the torsen figures the rears have more traction, so more power to them (tm).
Oversteer. Up to a point. As you add power to get out of the turn what
happens? Since the rears are "skidding" sideways, adding turbo power will
light them up, adding to oversteer, until, you've added so much power that the
rear axle is now spinning at or faster than the front (slip angle + track +
"power" <front> is less than or equal to slip + track + "power" <rear>
("power/torque/hp" by the way, really is just adding more slip and/or
track>less traction). At this point, the torsen senses a faster spinning rear
axle, slower spinning front. More power to the front. So now, you have
oversteer chassis attitude, WOT, with torsen transmitting torque to to the
front. Understeer. Hey there's more than that...
Sarge indicated, your line is for oversteer, because you are loading the rear,
back end out. Before the COG changes (especially in the big cars) the torsen
has already done it's job of sending power forward. So the back is down the
car loading the outside wheels, the inside wheel starts to lose traction
(lift, but doesn't have to be all the way, just enough to change the contact
patch area), and the inside front will start to spin. Why? The torsen is
sending the power to a front open diff, all forward axle torque in the front
open diff will go to that inside wheel.
Assuming all of the torsen properties have been transferred on a 300HP car at
WOT, that means the rear axle started the power turn with 225hp rear/ 75hp
front, oversteer (pick a number between 151 and 225, irrelevent, by physics of
the chassis (track and slip) and the torsen (power) it will be higher rear
than 150/150). In the middle of that turn at WOT, you just lost up to 150hp
from the rear wheel, and put that 225hp TO the inside front and 75hp to the
rear axle (and at this point who cares what the distribution of that 75 is in
the rear, you have your hands full right now). First hint of spin (=bite) is
here. Stay on WOT, the torsen senses the front wheel spin thru (faster axle
speed-front), transmits torque to the rear. The COG hower is rocking you
forward catching up to the off power rear attitude, and it will now need to go
back to the rear again. The torsen beats that however, and you now have a
rear inside wheel lifted, and all the power sent to that inside rear wheel.
Go at this full out, you will feel the COG oscilation, chasing the torsen
oscilation, one whacky feeling, btdt. Bite potential is really high here, cuz
you want to do something about that whacky stuff.
Now, If you aren't at a too radical chassis to apex, you can stay on the power
and understeer out. Too far, you MUST lift. Not all the way mind you, you
don't want that oscilating 225hp to take a snatch when it gains traction
again, with the chassis weight distribution at 57f/43 rear to boot. The above
scenario IS the bite. So what to do.
In my case, I go after a neutral attitude, steady throttle input to induce as
close to a 50/50 split to get around the apex, then work the go pedal again.
However, the further you are out, the longer that understeer slide is, for me,
potentially a really long long time. For some, maybe too long.
Sarge shared that you want to modulate just enough throttle to keep the torsen
"thinking" rear, bingo, the expert line. Better be darn good. A whole bunch
of factors affect where that line is: Tire pressures, chassis weight, tarmac,
rain gravel snow, etc.... I've been bitten with only tire heat as the
variable on a dry track at 8/10ths, so this is a delicate position folks.
Now, what happens if you need to avoid the kid on the bike, or you just don't
have any more road? You are up to your neck in spiders. You either must take
the spin, or hit whatever the apex has to offer. Neither sounds pleasing,
both take heroic instinct, and great finess. Why? Cuz everything you do
after you went too far, either with steering or pedal, has a torsen there to
add another variable.
So here is the bite, oversteer, understeer, oversteer, ad infinitum. Based on
torsen and car attitude to the apex. I'm really starting to like the
understeer, understeer, understeer of the Gen I cars. Very predictable, even
beyond the limit, no so with the Torsen.
Now, last addressed is the Bell curve, Ben and Randall's comments regarding
that 7/10ths. No problem with the thinking, it's what audi markets to as
well. As you can tell from many posts here, a lot of people haven't been
bitten, in fact, most haven't. I might also venture to say (and my point
really all along) is that it is YOUR best hope that you never have to venture
beyond the 7/10ths world where the torsen operates well. I say statistically
we hope to live less than a deviation from the mean. The reality of the Bell
curve is that, in order to have that very mean, you have 1, 2 and 3 standard
deviations.. Without naming names on this list of 1200, we know that a few
have ventured at least 1 deviation with unpleasant results. This is what I,
Jeff and a few others are looking at. Playing in the mean is easy and trouble
free, no doubt. To Ben, I say, your forays to Steamboat and it's cf has the
potential to bite ya sooner, I was in the car several times when it bit your
fair Valerie (all the stuffs she made with the torsen were on the INSIDE of
turns, interesting). I feel the hunt in an open diff Gen I and a Torsen just
driving in the rain or snow on the street. It's subtle but it sure is there.
I'm happy to be the guy 2+ standard deviations from the mean (many claim that
other than I). Understand too, that playing there is not for the timid, and
if you go there, it could your first and your last time, be prepared. A
warning message from this deviant Boy Scout with the "black widow" badge.