On my EM car, if I lower the front tire pressure by one pound. The front
end has more grip, and turns in better. That's my 2c....... What will
work for one car may not work for another. It's good to try different
things in autox. Ask KeS, he went from a C5 to a SUV, and is wondering why
he's not getting TTD :>)))))
Barry
At 02:53 PM 7/6/2001 -0700, Michael R. Clements wrote:
>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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