C.R. Krieger

Juhan Leemet <juhan@logicognosis.com> wrote in message news:<pan.2004.08.18.22.00.04.95635@logicognosis.c om>...
>
> Good explanations. Thanks!

You're welcome.

> FWIW, these days I'm driving an AWD Subaru (can't affort Quattro), so I'm
> buying new tires all round. They say that any mismatch in tire size causes
> the transmission to have problems ("blow up"?) so I'm not taking chances.
> I guess I'm avoiding bad rear traction problems as a freebie?

Not the transmission; the differential. Never actually heard of one
blowing up, either, even as sorely abused as some of 'em must be. As
long as your nominal tire size (outside circumference) is close to the
same, I wouldn't worry about it too much.

> I have to say that driving AWD "feels different" from RWD or FWD. I guess
> that's obvious? What's not so obvious to me is how to "get the hang of
> it". Whenever there's some snow, I try to find some clear space to
> "practice" slides, and handling when various wheels are "breaking free".

You need to learn that you'll still have FWD-style understeer at low
speeds and more neutral handling at higher ones.

> Thinking some more about it, I guess having good tires all around does not
> prevent spins. As you brake, the car pitches forward and you get more
> braking action from the front tires, and less weight (and hence frictional
> force) on the back tires. If they break free, they can still spin the car.

Bingo!

> I guess AWD driving technique is more like FWD? You should plan on braking
> early, then "powering though" turns: i.e. point in the direction you want
> to go and (gently) apply accelerator, not brakes?

The fastest way through turns with FWD is to add a touch of braking
when the front starts to slide (understeer) to induce some oversteer.
You can gently experiment with the handbrake on curves, if you're
adventurous and you want to feel the transition from under- to
oversteer. Rally drivers discovered this decades ago.

With AWD, you can lift off the throttle *if* you get understeer. You
can also accelerate until it starts to slide and get onto the gas
earlier because of the power distribution (which doesn't tend to
overload either end of the car when you do it). It's simply much more
forgiving.

> OTOH, I think I've
> experienced a sudden "oversteer" that resulted when the tires started to
> grip: the front wheels were pointed where I wanted to go and started to
> turn that way, but the rear wheels had some power applied towards the
> outside of the turn.

Could happen ...
--
C.R. Krieger
(Been there; done that)