Re: just when you thought the awd vs rwd thread was dead

[Dave Eaton <dave.eaton@minedu.govt.nz>]

yes, this thread has been beaten to death before.

facts:

1) quattro enhances grip in all weather conditons.  if it works in the wet,
then it works the same in the dry.  as walter rohrl said, "if it only gives me
another 2% in the dry, then i want it!"

2) by apportioning tractive forces over all 4 wheels, this leaves more grip at
the rear for cornering (than with a rwd) and at the front for steering (than
with a fwd).  with a rwd car, with *no* tractive loads through the front
wheels, total grip is used for cornering, braking and steering.  hence less of
a tendancy to understeer relative to a fwd or awd car.  key word is tendancy. 
however with rwd, all the tractive loads are transmitted through the rear which
means that there is less grip available for cornering (and braking).  hence the
tendancy to oversteer.

think of it as though each tyre has 100 units of total grip.  from each of
these you must subtract a quantity for traction (motive power), steering and
braking.  what is left over is available for cornering.  think this though and
you will see that, in most situations awd is a winner.

for example, say at a particular instant, you are suppling force which needs 40
'units' of grip (to avoid slip), and need 20 units of grip for steering.  (ie.
you're on a slightly trailing throttle steering around a bend).

fwd: each front tyre has a total of (100-40/2 - 20/2)=70 units left for grip. 
each rear tyre has 100-0 = 100 units available for grip.  hence a tendancy to
understeer.

rwd: each front tyre has 100-20/2=90 units left for grip, each rear 100-40/2=80
units left for grip.  hence more oversteer.

awd: each front has 100-40/4-20/2=80 units for grip, each rear 100-40/4=90
units.  result, more neutral handling, more front end grip than fwd, less than
rwd, more rear end grip than rwd, less than fwd.

the most common complaint about awd is lack of 'steering feel'.  this is
because of the use of the front tyres to transmit tractive forces which
'muddies' the steering feel, as it does with a fwd machine.  this is
compensated for by good design (witness the a4 vs 80/90, and best of all the
ur-q 20v) and good driving.

3) a lot depends upon driver skill as to relative merits of 2 cars.  for
example, as has been pointed out one of the reasons for a rwd car's tendancy to
oversteer on braking into a corner is weight transfer to the front and the
unloading of the rear tyres.  the same effect can be used deliberatley by a awd
or fwd driver to minimise *understeer* by making the front-end "bite" on turnin
(weight transfer means more relative grip).  hence the advice to back-off the
throttle in a awd or fwd car if your're running wide.

4) awd has been banned in every racing category i know off (f1, touring cars
[fia class 2], gt, imsa, etc)- except fia class 1 which died last year anyway. 
in that category (450hp, active suspension, carbon/carbon brakes etc), 2 of the
contenders were awd (opel and alfa) while one was rwd (mercedes).  honours were
about even, although open won the last year, and alfa the first 2.

4) i've never been toasted by an m3 yet.  and we get the full blown ones here. 
btw in the wet, the m3 is a huge joke with it's slow (or no) slippery diff.  in
the dry it is a fast and capable car which can still swap ends quite easily and
gets nervous at speed.  i've driven one fast for about 600km's and thought at
the time that, apart from the sub-standard fit and finish, it was a fine car
for a rwd, but a relatively hard one to live with day-to-day.

the ur-q woudld see off an m3 on a tight and twisty road but would be toast on
a track in the dry (brakes & performance).  the rs2 (same power, equivalent
brakes) would make it much more even.  on the open road, the rs2 would eat (and
has) the m3.  put a better friver in the m3, and i'd be in the brown smelly
stuff...

cheers,
dave
'95 rs2
'90 ur-q

>
>Igor, take a gander at your sig. line.  Although I haven't had the pleasure
>of riding in your 200 I have seen its profile in the Quattro Quarterly.  A
>very nice car.  If I was there for the showdown with your friend I would put
>all my chips on you as well.  You're driving a Kessel 200 not an Audi 200
>;-).  (18 psi, full suspension, bypass valve, short shift mod, big wheels &
>tires, etc.)  A more appropriate match-up would be a stock M3 or 540i or
>lets up the ante - any one of those tuned monsters profiled in EC - Golf,
>318, Jetta, Volvo.
>
>Matt
>89 200TQW
>
>------------------------------