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UNDERSTANDING TIRE PRESSURE
AND LOAD LIMITS
Tire inflation pressure is the level of air in the tire that
provides it with load-carrying capacity and affects the
overall performance of the vehicle. The tire inflation
pressure is a number that indicates the amount of air
pressure– measured in pounds per square inch (psi)–a
tire requires to be properly inflated. (You will also find this
number on the vehicle information placard expressed
in kilopascals (kPa), which is the metric measure used
internationally.)
Manufacturers of passenger vehicles and light trucks
determine this number based on the vehicle’s design
load limit, that is, the greatest amount of weight a
vehicle can safely carry and the vehicle’s tire size. The
proper tire pressure for your vehicle is referred to as
the “recommended cold inflation pressure.” (As you will
read below, it is difficult to obtain the recommended tire
pressure if your tires are not cold.)
Because tires are designed to be used on more than one
type of vehicle, tire manufacturers list the “maximum
permissible inflation pressure” on the tire sidewall. This
number is the greatest amount of air pressure that should
ever be put in the tire under normal driving conditions.
CHECKING TIRE PRESSURE
It is important to check your vehicle’s tire pressure at
least once a month for the following reasons:
Most tires may naturally lose air over time.
Tires can lose air suddenly if you drive over a pothole or
other object or if you strike the curb when parking.
With radial tires, it is usually not possible to determine
under-inflation by visual inspection.
For convenience, purchase a tire pressure gauge to
keep in your vehicle. Gauges can be purchased at tire
dealerships, auto supply stores, and other retail outlets.
The recommended tire inflation pressure that vehicle
manufacturers provide reflects the proper psi when a
tire is cold. The term cold does not relate to the outside
temperature. Rather, a cold tire is one that has not been
driven on for at least three hours. When you drive, your
tires get warmer, causing the air pressure within them
to increase. Therefore, to get an accurate tire pressure
reading, you must measure tire pressure when the tires
are cold or compensate for the extra pressure in warm
tires.
