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From: cramer@kontron.UUCP (Clayton Cramer)
Newsgroups: net.auto
Subject: Re: tire inflation pressures
Message-ID: <377@kontron.UUCP>
Date: Wed, 17-Jul-85 22:01:04 EDT
Article-I.D.: kontron.377
Posted: Wed Jul 17 22:01:04 1985
Date-Received: Tue, 23-Jul-85 05:10:00 EDT
References: <572@hlwpc.UUCP>
Distribution: net
Organization: Kontron Electronics, Irvine, CA
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> I just bought new Michelin XH tires for my not-very-sporty
> 1980 Chevrolet Malibu, and the guy who installed them told
> me to keep the pressure at 34-35 pounds cold.  That's the
> pressure listed on the sidewall as maximum.  I've always
> kept my tires inflated to the manufacturer's recommendation
> printed in the manual and the door sticker (which for my
> Malibu is 26 pounds in front and 29 pounds in the rear)
> When I questioned the tire installer about his, he said
> in no uncertain terms to ignore the mfgrs. recommendation
> and keep them filled to the tire maker's maximum.
> 
> Seems to me the installer should know his tires, but I'm
> reluctant to believe him without further comments.
> Can anyone confirm or deny this recommendation?
> 
> Carl Blesch

Within certain limits, tire pressures are a trade-off.  Higher
tire pressures increase cornering and dry traction; they also
make the ride rougher, and increase the danger of sharp objects
penetrating the tire.  Most important, high pressures reduce 
sidewall flex, which reduces heat buildup, which reduces the
risk of catastrophic tire failure.

For a long time, GM (and most of the other US car makers), have
recommended pressures around 24 to 28; in the last several years
they have started recommending higher pressures in order to 
improve gas mileage.

Differential tire pressures front to rear can produce differing
levels of oversteer and understeer --- although I have yet to
get a nice simple relationship to describe the effect that isn't
dependent on the car.

When in doubt, increase pressures to the maximum specified on
the sidewall.