I agree with all that is said, but something has been left out. Your
motor doesn't have infinite horsepower and if you can now almost call the
auto-X course a drag race with the curves meaning little, until the thing
tips over, dependant I think on center of gravity only, and if you have to
slow down when it gets on two wheels you do it all over again. In either
case the lighter car will definitely win. This same effect is what keeps
very hard tires on my Ford Explorer, with the stock rubber it doesn't
generate enough grip to roll,... usually.
This must really be a slow auto-X day...
Charles Brown
90 Miata EM
----- Original Message -----
From: <dg50@daimlerchrysler.com>
To: <autox@autox.team.net>
Sent: Monday, August 07, 2000 12:10 PM
Subject: Classing Cars with Physics
> I while back, I observed that a small, light, low-power car would perform
> varyingly well against a large, heavy, powerful car, depending on the
> layout of the course, and that perhaps some metric needed to be developed
> that would allow courses to be indexed.
>
> At about the same time, Jean proposed the 'Evolution Theory of Car
> Classing' in which representatives of current cars would be brought to a
> test site, Evo school drivers would drive them, and then classing
decisions
> made based on the results.
>
> The first idea has tremendous merit, but is very difficult to determine
> (although Roger had a neat idea about collecting average speed statistics,
> which I like because it's so simple - and I'm going to write up something
> on this after Nationals)
>
> The second idea is very easy to pull off (the main problem being one of
> logistics), but - sorry Jean - is lacking in merit due to the number of
> variables involved. (Not to mention perception issues)
>
> But then I started really thinking... let's say we take Jean's idea, and
> start eliminating variables. Let's take a selection of cars, and a
> selection of drivers, and run them through a series of discrete elements -
> 0-60, 60-0, 100m skidpad, slaloms of varying lengths and gaps, and so on.
> When done, you'd have a sort of data "toolkit" that could be used to
string
> together an approximation of a given course. For example, the prototypical
> ProSolo course: Straight, into slalom, into 180 turnaround, into slalom,
> into lane change, into finish. So 0-60 gives you time down the straight,
> the appropriate slalom data gives you the slalom entry speed, so working
> backwards from the entry point using the 60-0 data gives you braking point
> for the slalom. Same deal for the turnaround, etc - skidpad tells max
> lateral G, which in turn gives max entrance speed, which can be determined
> how is to be reached with 0-60 and 60-0 data. String it all together, and
> you get a theoretical "best lap".
>
> Now that "best lap" may or may not actually _be_ the "best lap" possible
> ("after all" quoth Concord "It's only a model") but it should be
consistant
> from car to car - the model may break down in places, but it would break
> down the same for all cars, and as long as the failings don't favour a
> given kind of car, all the relative performances should be the same. Which
> might, maybe, make this a useful technique for classing cars. Maybe.
>
> Say, here's another thorny thought. I have 2 cars: they are the same
> dimentionally (length, width, height, wheelbase etc) They have
> infinite-grip tires. They have the same power/weight ratios, and the
weight
> distribution is the same. One weighs 1000lbs more than the other. Which
car
> is faster, or are they tied?
>
> DG
>
----- Original Message -----
From: "Bill Fuhrmann" <bfuhrman@isd.net>
To: <dg50@daimlerchrysler.com>; <autox@autox.team.net>
Sent: Monday, August 07, 2000 3:48 PM
Subject: RE: Classing Cars with Physics
>
> > Of course, but we're not testing tires here.
> >
> > I'm trying to understand how much effect weight really has on
performance.
> > Is weight just "power", spelled differently, or does it play other
roles?
> > Obviously, there's an inertia element, but if I have infinate-grip
tires,
> > does inertia really matter? Is "small" more important than "light" in an
> > autocross setting?
>
> It is more than a version of horsepower. Every time you try to change
> direction in a car, your car has to fight the tendency for the larger mass
> that is trying to go straight. This upsets your suspension geometry.
> Unless you have the mythical perfect tires, it will fight against the cars
> ability to keep them on the ground.
>
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