Re: Differentials

[Eliot Lim <eliot@u.washington.edu>]

On Mon, 30 Jan 1995, Jason Arthur Filuk wrote:

> Well, my old 5000 S with practically bald Pirelli p500 never would lose its
> tail negotiating a snowy turn .  It seems odd that with a quattro one
> would require the security of snow tires to keep the car in control.  I 
> guess quattro shows its true superiority in wet rather then snowy conditions?

the danger of any 4 wheel driven vehicle is not the vehicle itself but
rather the false sense of security that it imparts under slick
conditions.  driven at the same speeds i doubt if a quattro is any
more lethal than a fwd 5000 (probably less, since you have 4 wheel
engine braking), but the point is that with better traction and better
stability the chances are that the quattro driver *would* be driving
faster than the fwd 5000 driver, while it will not stop or steer any
better.

snow tires on a quattro are for steering and stopping, not for going,
which it does supremely well on anything. 


> Reading my manual last night , it says that on dry roads the quattro 
> (audi 90) behaves like a fwd car (but i would assume power is distributed 
> evenly among all 4 corners)

the quattros are set up for slight understeer rather than 100% neutral
because these cars use up much more of the total amount of adhesion on
4 wheels than 2wd cars.  on a 2wd it is far less likely that both ends
run out of grip at exactly the same time.. with 4wd and a torque
redistributing center differential it is far more likely and the car
would be far less predictable and controllable in these circumstances.
thus some understeer is dialed in to provide a "safe" and predictable
"fwd-like" behavior.


eliot