Thanks for all the help everyone. I've concluded that after every run, I
should raise or lower my tire pressures to induce a certain handling
characteristic. However, I have a very limited amount of time (ASP) since
there are so few cars running in my group. Is it legal to leave your
equipment on the grid?
THanks
Larry
----- Original Message -----
From: "Michael R. Clements" <mrclem@telocity.com>
To: "John J. Stimson-III" <john@idsfa.net>; "Lawrence Lane"
<firstcard@hotmail.com>
Cc: <barx7club@rx7.org>; <BA-AUTOX@autox.team.net>
Sent: Friday, July 06, 2001 2:53 PM
Subject: RE: [3] Oversteer Understeer
> I've found a simple technique that seems to work well over the years with
> different cars & tires. Chalk the corner of the tire and keep dropping the
> pressures until the tire rolls into the chalk, then bump up the pressures
a
> PSI or two. This worked on the BFG R1s, the Kumhos, and also on the
> G-Forces, with my '95 RX-7 and my Panoz. The point where I measure the
> maximum cornering Gs on my accelerometer, and the best autox times, was
the
> point where the tire had just enough pressure to prevent rolling into the
> chalk.
>
> In other words, less pressure generally provided more grip, as long as the
> tire was not so low that it was rolling onto the sidewall. That is, use
just
> enough pressure to maintain the tire's shape, and no more.
>
> After you have discovered this optimal point, you can adjust up or down a
> PSI or two in front and back to make small tuning adjustments to
understeer
> vs. oversteer.
>
> As you can see there are varying opinions on this. I am merely citing my
own
> experience, which is limited to two fairly light and well balanced cars,
> both with stiff suspensions on R compound tires. It might work differently
> for different cars or different tires.
>
> -----Original Message-----
> From: owner-ba-autox@autox.team.net
> [mailto:owner-ba-autox@autox.team.net]On Behalf Of John J. Stimson-III
> Sent: Friday, July 06, 2001 14:10
> To: Lawrence Lane
> Cc: barx7club@rx7.org; BA-AUTOX@autox.team.net
> Subject: Re: [3] Oversteer Understeer
>
>
> It does depend on the tire, but in general there is a "sweet spot"
> which provides the maximum grip. Below that pressure, the tire is too
> soft and tends to roll over onto the side of the tread and/or lift the
> inner edge. Above that pressure, the tread bulges a bit and reduces
> the area of contact between the tire and the ground.
>
> There is also a secondary effect described by Andy Hollis, wherein
> higher pressures increase the effective spring rate of the tire. If
> the effective spring rate of the tire is comparable or softer than the
> spring rate of the suspension, then changing the spring rate of the
> tire can have a significant effect.
>
> At your next event, ask someone to show you how to use chalk or shoe
> polish to judge your inflation pressure.
>
> On Fri, Jul 06, 2001 at 12:18:44PM -0700, Lawrence Lane wrote:
> > I was told at the track by someone I met that the more air pressure is
> given,
> > the tire will have more traction. I thought this sounded weird, but I
> thought
> > I'd try it out. So, I inflated my 18"s to 35 in the front and 40 in the
> rear
> > to decrease oversteer. I'm not sure if it was the car or not, but I
> > experience a huge amount of oversteer. What is the general rule about
> this?
> >
> > Thanks
> >
> > Larry
> > FD3S
>
> --
>
> john@idsfa.net John Stimson
> http://www.idsfa.net/~john/ HMC Physics '94
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