Spider bite revealed!

[Mike Arman <armanmik@n-jcenter.com>]

>>
>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.
>
>This assumes all variables the same as 885140 except accleration(Trg)=cf 
>(they are the same variable for all intents and purposes).  Changing *any* 
>variable, *can* increase or decrease the chances of Bite, but can't
eliminate 
>it.
>
>Single yes/no question Dave (/others):  Looking at the above scenario v your 
>research, isn't the definition of bite as I presented above, possible (I 
>didn't ask: *likely*)?  After the answer, you(/others) are welcome to
address 
>the errors of my thinking.
>
>HTH
>
>Scott Justusson


Dang it guys, that's EXACTLY what I said!!!!

Now that we have a working definition of it, we need to discover what
provokes the spider to bite.

Base assumptions: Car is being driven hard. For purposes of discussion, 50%
is assumed to be normal street driving, 75% "spirited" street driving, 90%
racing (on _race_track_), 97% racing and really pushing hard, and at 101%
car goes off road simply because c/f of tires has been exceeded and NOTHING
will keep you there.


1. Most of us really don't drive that hard. We are probably mostly in the
55 to 70% range, at which even things like incorrect wheel alignment just
doesn't matter that much. The spider never bites us simply because we are
not pushing hard enough to provoke it.

2. Incorrect wheel alignment tends to lower the percentage level at which
the spider bites. If the mis-alignment is bad enough, the car can become
uncontrollable as early as 70 or 75%. Correcting this raises the "bite
percentage" to 90 or 95%, which is well beyond the levels of even
"spirited" street driving. (My suspicion is that this supports Phil's
contention that proper alignment "cures" spider bite. In fact, proper
alignment means the spider bites "later" - I doubt Phil drives at 90 or 95%
on public roads - he's far too smart for that.)

3. At 90 to 95%, assuming a properly set up car, aligned, tires good,
reasonably skilled driver, etc., we are *just* short of spider bite. The
trick is to realize that spider bite seems to occur AFTER the LAST WARNING
you get before control is lost - note that I didn't say "before you lose
control". If you push to 101%, there's nothing you can do to maintain
control anyway, and you are going off-road.

4. At 97%, we are so close to the edge that a patch of gravel, a spot of
oil, a puddle of water, whatever, will push us over the limit, and we are
gone. If we are already at 97%, pushing harder (accelleration!) quickly
takes us to 101%, and the spider promptly bites - just like Scott says
(accelleration makes it worse!).

I *think* this explains why the racers among us insist spider bite is real
- because at 97% it is. I also think that this is why Phil says "alignment
cures it", because at 75%, it does.

Finally, I think we need to determine the severity of the spider bite. In
Phil's case, it was an utter and absolute loss of control and end for end
spin into the countryside.I honestly think he could do that again even in
his now-properly aligned car if he simply took the exact same turn 20%
faster than he does now. The impression I'm getting is that "spider bite"
is a FAILURE MODE - we have simply pushed the limits of the device too far,
and this is how it reacts.

What is deceptive to us and scary to us is that the infamous Torsen seems
to behave itself very well and DOES give us the Quattro Advantage, UNTIL we
push it just too far, at which point it gets spectacularly confused and
blows the whole show, all at once, suddenly, big time.

Best Regards

Mike Arman

(Who drives his non-turbo 2WD UR-5K at about 40%, most of the time.)