Greg,
Welcome to the sport! I hope you find it as enjoyable as I do. I think you
will.
The reason they suggest bumping up the air pressures is to avoid damage to
the tire and wheel. In an autocross, you will be pushing the tires much
harder then you are likely to ever do on the street. It is feasible that a
tire could roll over so much that the rim might dig into the pavement and
possibly upset the car, and when I say upset, I mean upside down. :-O
Running with a higher pressure effectively firms up the sidewalls and helps
keep the bead seated on the wheel. It will actually help the handling at
lower speeds since you will be keeping more of the tread compound on the
road and less of the sidewall.
The chalk method works pretty well on street tires. Autocross tires with
stiffer sidewalls need to be set with a pyrometer or based on reading the
wear. Your best bet in both cases is to consult someone with a similar car
and get recommendations. Posting to Team.net is a great idea.
I autocross a '90 CRX in Street Prepared, so I don't know *exactally* the
right pressures for your car, but I would recommend 38-40 psi in front and
35-38 in the rear. Check your tires after your first run to make sure you
don't have wear way up the sidewalls and slowly lower the pressure until the
tread is wearing up to the edge of the tread blocks where they meet the
sidewall.
This means checking your tires after each run. Hopefully your next event
will be run so that this shouldn't be a problem time-wise. If you don't
think you will have time to check the tires between runs, then ask someone
to help you. Don't feel bad about asking for help. Chances are, there will
be lots of people glad to assist. If possible, try to get someone with lots
of experience. The event chairman or the chief safety steward could
recommend such a person.
Good luck!
Brian Meyer
Wichita Region SCCA
> ----------
> From: Greg and Valerie Holden[SMTP:gholden1@nycap.rr.com]
> Sent: Thursday, May 27, 1999 9:08 PM
> To: autox@autox.team.net
> Subject: Tire pressure for Michelin XGTV4's
>
> Hello from an autox novice.
>
> I will be running my first autox on 6/20 and am wondering about tire
> pressure. I have a 96 Integra GS-R with stock suspension, wheels and
> tires. Tires are Michelin XGTV4 195-55-15.
>
> I went to an autox last week that got rained out. Before going, I upped my
> tire pressure to 38psi front and 36psi rear (up from 36f, 32r factory).
> The car feels less stable in high speed (70mph) sweepers with this
> pressure. Traction is also worse. All the FAQs say to boost pressure until
> chalk marks tell you you're not rolling onto the sidewall. Is this advice
> meant soley to avoid tire damage? I don't understand how losing traction
> and stability is going to help me at an autox.
>
> Has anyone run a stock GSR in autox's? What pressures did you use?
>
> Thanks in advance for any input.
>
> Greg Holden
> 96 Integra GSR
> MoHud SCCA
>
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