Pontiac 1999 Firebird Owner's Manual page 295

Inflation -- Tire Pressure
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The Tire Loading Information label, which is on the
rear edge of 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 1 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 kPa), whichever is lower. See the example below.
-
When you end this high speed driving, return to the cold
inflation pressure shown on the Tire
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.) @ 300 kPa (44 psi) Max. Press.
For this example, you would set the inflation pressure
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for high speed driving at 38 psi (265 kPa).
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Loading
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:
D
Too much flexing
D
Too much heat
D
Tire overloading
D
Bad wear
D
Bad handling
D
Bad fuel economy.
If your tires have too much air (overinflation),
you can get the following:
D
Unusual wear
D
Bad handling
D
Rough ride
D
Needless damage from road hazards.
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