Pontiac 1998 Firebird Owner's Manual page 298

Inflation
--
Tire Pressure
The Tire-Loading
Information label,
which is on
the
driver's door, shows the correct inflation pressures
for
your tires when they're cold. "Cold" means your vehicle
has been sitting for at least three hours or driven no
more than I mile (1.6
km).
If you'll be driving at high speeds (e.g., speeds of
100 mph (160 km/h or higher), where it is legal, set
the cold inflation pressure to the maximum inflation
pressure shown on the tire sidewall, or to 38 psi
(265 Wa), whichever is lower. See the example below.
When you end this high-speed driving, return to the
cold inflation pressures shown on the Tire-Loading
Information label.
Example:
You'll find maximum load and inflation pressure
molded on the tire's sidewall, in small letters, near the
rim flange. It will read something like this: Maximum
load 690 kg (1521
lbs.) 0
300 kPa (44 psi) Max. Press.
For this example, you would set the inflation pressure
for high-speed driving at 38 psi (265 Wa).
NOTICE:
Don't let anyone tell you that underinflation or
overinflation is all right. It's not. If your tires
don't have enough air (underinflation), you can
get the following:
0
Too much flexing
0
Too much heat
0
Tire overloading
0
Bad wear
0
Bad handling
Bad fuel economy.
If your tires have too much air (overinflation),
you can get the following:
Unusual wear
0
Bad handling
0
Rough ride
0
Needless damage from road hazards.
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