Wolfgang Pawlinetz > wrote in message >. ..
> "Fred W." <Fred.Wills@allspam myrealbox.com> wrote:
>
> >> The rearwheel drive is fun and with all the electronic gimmicks it
> >> will really do it's job. However at a certain climb angle or even
> >> slipperyness of the road, the rearwheel drive gives in, then the FWD
> >> and then the quattro.

You should be saying "AWD", not "Quattro", as that covers *only* Audi,
and it is well-known that BMW and others *also* build AWD cars.

> >Sorry, no. This is contrary to the laws of physics. If you assume equal
> >axle weights, as the car climbs it places more weight over the rear axle and
> >less over the front. So a rear wheel drive car would have an advantage over
> >a FWD in climbing.
>
> You almost got me there :-)

No; he *does* have you there.

> There's sort of a thinking error in your statement. It took me a while
> to do the math (i.e. mechanics) but the outcome is, that the ratio
> front/rear with regard to the friction force does _not_ change.

Yeah; it does.

>
> The |
> V indicates the direction of Fn
>
>
> ____
> __/ | \__
> |_ __V___ _|
> ____U______U_____
>
> So far so good.
>
> Now the worst case example:
>
> Tilt the road and car 90° (don't sit in the car).
>
> __
> | | |
> |C \
> | | |
> | | |
> |C /
> | |_|

What you overlooked is the *practical* 'worst case example': 45
degrees. [This assumes that the tires can generate 1.0g of tractive
force, otherwise the car slides down the slope.] Notice, at 45
degrees, where the CoG is. Depending on how high above the surface it
lies, it could come to rest directly *over* the rear axle (even
*behind it* in a tall or rear-heavy vehicle). At any rate, as long as
it *is* above the surface, it will shift *toward* the rear axle as the
angle increases. If you want a simple demonstration of this, think
about moving a refrigerator. Lying on its side, the top part could be
pretty heavy, but as you tilt it up, the upper end becomes lighter and
lighter until you have shifted the CoG past the point where the bottom
edge is on the floor. Then, the top side weight becomes *negative*
and the thing falls over the other way. Therefore, a slope *does*
influence the amount of weight (and traction) on the wheels on each
end of the car, even if it's sitting still.
--
C.R. Krieger
(Been there; dropped that)