spider bites - oh, no, not again!

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

Well so far, the distance I've kept from the spider bite flame war has been
safe - here are some of the comments I've gotten back so far:


>
><< If what I am saying here bears even the slightest relation to reality, it
> seems to me that most of us, who do NOT drive our cars at or even near
> their limit of adhesion, will never experience this spider bite.  >>
>
>I am not smart enough to understand the argument, or if you got it right.

Frank - *I'M* not sure *I* understand my own argument or if I got it right
either! What I'm trying to do is look past the flames on this topic and see
what it is they were originally fighting about. Copyright technicalities
regarding public posting of SAE papers, while utterly fascinating, don't
have much to do with "why-my-car-spun-off-the-road".


 I 
>do however think you are wrong in your assumption that those of us not 
>competing on the byways are immune. I let the back 2 tires on my first
Audi Q 
>(1989 90) and one day on an entrance ramp something really strange happened 
>which resulted in me leaving the roadway. I have played around in snow 
>forcing skids etc but I can still recall the confusion I felt that day. I
for 
>one am not so quick to dismiss the bite of the spider.

I may very well be wrong. So far, I have actually not been able to get a
clear description of what this really is. Again, what I *think* I'm hearing
is that quattros can sometimes behave unpredictably when pressed hard, but
so far, I have no real indication of HOW hard and HOW unpredictably. Since
I can't remove the torsen from my car, what I'm trying to find out is how
it behaves under various circumstances.

I don't dismiss it at all - I'm still trying to define it. 

>Frank Santoro
>1990 V8
>1998 A8

Frank later sent me a PS as follows:

> (1989 90) and one day on an entrance ramp something really strange happened 
> which resulted in me leaving the roadway. I have played around in snow 
> forcing skids etc but I can still recall the confusion I felt that day. I 
>for 
> one am not so quick to dismiss the bite of the spider. >>
>
>Heck- I wasn't even smart enough to include the two most important pieces of 
>info: It was a cloverleaf ramp, and it was raining. I was moving , but not
by 
>any means "on the edge" when it happened.
>
>

First thing I note is that the car is a 90 - light car, most of the weight
on the front anyway. I almost suggested hydroplaning, but then I remembered
that hydroplaning is independent of vehicle weight, and occurs (if other
conditions are also right) at 8.3 times the square root of the tire
pressure. Unless the rear tire pressures were lower than they should have
been? Until we know exactly what spider bite is, and can reproduce it at
will (do this, this, and this, and this will happen - EVERY TIME), I am
reluctant to say that any given off-road excursion was caused by spider
bite. The jury is still out, and I have NOT made up my mind as to what's
going on here - that's what I'm trying to find out. The fact that you
experienced a similar problem at LOW speeds either adds a datapoint to
spider bites or simply means the car went off-road for other reasons.









Phil then says:

>
>> If I understand that correctly, when the car enters the corner, the driver
>> turns the wheel and the car doesn't turn as much as he expects (continues
>> to go straight), so he turns the steering wheel some more. Next thing that
>> happens is that the car begins to suddenly oversteer, and dives toward the
>> inside of the turn. Finally, the car returns to the understeer condition.
>> The resultant path through the turn is a lurching zig-zag, and the driver
>> emerges somewhat puckered. This non-linear response to steering inputs is I
>> think what is being called spider bite.
>
>No, I think what you describe is definable as 'controllable'.  The
>experience I had just after taking delivery of my 100TQW was definitely
>NOT - it was highly unpleasant, just as Scott has described it.


I clearly missed the description of spider bites being uncontrollable
instead of just disconcerting. Understand that I am in no way trying to
impugn your driving skills, but is it possible that you were just still
slightly unfamiliar with your new Avant; a larger and heavier car than your
URQ, and simply pushed it too far? A type 44 Avant is also taller and has
more weight in the back than a URQ - the suspension geometry is different,
and I'm willing to bet that *your* URQ's suspension is in a FAR better
state of repair than almost ANY type 44 on the planet!

>
>Power input is crucial - trailing throttle or neutral throttle turns
>don't (IMO) stand a chance of producing this phenomenon.

>From this, I think that spider bite is most likely to be experienced in
high speed turns, while trying to go still faster. Eventually, no matter
what techno-gadgets the car is equipped with, we ARE going to exceed the
limits of tire adhesion, and we ARE going to go off the road.  It sounds
like quattro, torsen, haldex, et al, simply delay this to higher speeds
than could be achieved with non-Q cars (duh!), but cannot elminate it.
Simply put, if you go too fast, you will crash.

Tentative theory is as follows:

Push a quattro to 8/10, it handles "normally". (8/10 for a quattro is 12/10
for an non-quattro car.)

At 9/10, the handling gets squirrely as the quattro system attempts to
maintain/recover control. This is a clear message to slow down.

At 10/10, you are on the verge of total loss of control. Push harder and,
and you will get to test your energy absorbing bumpers and air bags.

URQ's are not as subject to spider bites as type 44s, because URQs are
lighter (which means they have less momentum when they start to go
sideways), have different weight distribution, and different suspension
characteristics (sportier) than type 44s.

Type 44s are sensitive to wheel alignment and tire pressures. If these are
off, handling can become unpredictable.


>
>I'd never experienced it on a Torsen Type 85.  I didn't realise how
>downright wild it is until the Type 44 event.  This is 'scary' with
>a capital "Oh, SHIT!!".
>

If this were a non-quattro car, and Phil were not the driver, I would
simply say the cause was driving too fast for conditions. Since it is and
he was, I am going to wait for more information before deciding anything.

I also note that after a proper wheel alignment (part of which is getting
the tire pressures exactly right), the same driver in the same car at the
same speed did NOT experience the problem. It sounds like it comes on
SUDDENLY and with little or no warning - which could make it dangerous. 

>- --
> Phil Payne
> UK Audi quattro Owners Club


Finally, Huw Powell asks:

>
>> predictably (which builds driver confidence) until the limit of adhesion at
>> the rear is lost, and you go spinning off the road (how's THAT for
>> understeer?)
>
>great post!  but that rear engine spinout is oversteer, isn't it?
>
>remember, in the torque sensing flame wars a typo can cost you an awful
>lot...
>
>-- 
>Huw Powell
>

At the risk of getting spattered with semantics, my feeling is that no, a
rear engine spin-out is not oversteer. In this situation, the front end is
still going around the curve (either understeering, oversteering, or even
steering correctly!), but the traction has been lost at the back (heavy)
end of the car. The resultant momentum of the heavy end of the car now
controls the direction the car will take, not the way the steering wheels
are pointed. The fact that the front wheels still have some traction (or at
least more than the rear ones) results in the spin - the car rotates
completely, instead of just skidding. Eventually, enough energy is
dissipated by scrubbing the tires sideways that the car slows down enough
so traction is regained, and the spin stops. Yellow powder coating does
help, or so I have been led to undertand!

(This too, could be completely wrong! I was exploring "spider bites", but
somehow got sidetracked . . .)

Stay tuned for the next thrilling installment of Torque Wars, brought to
you exclusively by the Quattro List!

Best Regards,

Mike Arman