Re: FWD Beats Similar RWD on the racetrack Worldwide!

[Richard Welty <rwelty@xxxxxxxxxxxxxxx>]

On Wed, 16 Apr 2003 12:59:04 +0200 Phill Erasmus <erasmusp@domain.elided> wrote:
> So yes, forget about your old technology FWD (164s included) cars with
> it's inherited funnies like torque steer and so on, today's small to
> medium sized FWD are much quicker and nimbler in the twisties and race
> tracks than it's similar sized (and powered) RWD cars! Please note I am
> saying TODAY'S FWDs,

i'd held back, but now i have to speak up.

in general, when a racing series is based on street cars, some effort is
made to equalize the competition, often with weights, wheel/tire size
restriction, restrictor plates in the intake tract, etc.

in an earlier posting, someone whose name hasn't stuck with me used the
phrase "all other things being equal".

trust me, in touring car racing, all other things are not equal. touring
car racing in europe, from what i have seen, is meddled with constantly by
race officials trying to maintain equality.

i commend Alfa for making FWD cars devastatingly competitive in a tough
series. that still doesn't address the fundamentals of vehicle dynamics.

the issue is with contact patch and weight transfer. all cars transfer
weight from one end/corner to another as they change their attitude. when
you stand on the throttle while traveling in a straight line, weight
transfers off the front wheels and onto the rear wheels. when you stand on
the brake pedal while traveling in a straight line, weight transfers from
the rear and onto the fronts. when you corner in a constant attitude,
weight transfers from the inside tires to the outside tires.

where the weight increases, the contact patch increases, linearly up to a
point, but not in a 1:1 proportion -- that is, as you give up on one tire,
you gain on another, but not equally -- you always give up more than you
gain.

how does the drive system factor in? when you are on the throttle, with
weight moved to the rear, where are your drive wheels? if in the front, you
now have less traction to use when applying power. if in the rear, you now
have more traction to use when applying power.

let's suppose you are in the braking zone on the main straight at lime
rock. you start braking at maybe 3. there is at this point in time, no
difference between FWD and RWD.

at the 1 marker, you start to turn (turn 1 at lime rock is that rare
exception to a general rule, a place where an early apex can be a fine
idea.) you roll off the brake gradually as you turn in, also gradually
(turn 1 at lime rock is also a place where most any car responds well
to trail braking.) no difference between FWD and RWD yet.

at this point, the difference kicks in. you're turning, and balanced,
you're transitioning from brake to throttle, so the car is mostly weight
biased towards the outside. as you go to the throttle, the weight starts
shifting rearward. if you have a FWD car with lots of power, this is where
it gets tricky. you are putting power down through the wheels that are also
steering, with weight moved heavily towards the wrong end of the car.

this is where you are at the point that all FWD cars seemingly tend towards
power understeer. you are on the edge with not really enough grip for all
the demands you are putting on the tires.

RWD cars can also suffer from power understeer, but because it's only a
case of overstressing the front tires due to a bad choice of line & entry
speed, you can fix it by changing your entry.

the methods for improving the behavior of FWD cars in this cornering state
generally involve things not relevant for street cars, like massively stiff
suspensions that get rid of lots of the weight transfer. you could do it in
your street car, but it'd hurt way too much for daily driving.

i see FWD cars beat RWD cars all the time. there are well prepped VW
rabbits and golfs that can win in SCCA ITB at Lime Rock, against similarly
well prepared Alfas with similarly skilled drivers. the VWs typically have
smaller engines (1.8 vs 2.0L), but also have significantly less weight
(by several hundreds of pounds.)

all other things are _never_ equal. especially in racing.

richard
--
Richard Welty                                         rwelty@domain.elided
Averill Park Networking                                         518-573-7592
              Unix, Linux, IP Network Engineering, Security
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