tuning steer characteristics with tire pressure is a last-resort measure
because it reduces the total grip of the car.
in a stock class you dont have many choices; in an SP class, it is better to
do bar tuning.
HOWEVER, i recommend you totally forget about your tire pressures and
anything about the car until you have driven 10-20 events. it just doesnt
make much difference, and you might be adjusting the car to an incorrect (or
unoptimal) driving technique. its all about the driver.
-james
----- Original Message -----
From: Lawrence Lane <firstcard@hotmail.com>
To: Michael R. Clements <mrclem@telocity.com>; John J. Stimson-III
<john@idsfa.net>
Cc: <barx7club@rx7.org>; <BA-AUTOX@autox.team.net>
Sent: Friday, July 06, 2001 3:30 PM
Subject: Re: [3] Oversteer Understeer
> 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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