18
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 kilo pascals (kPa), which is the metric
measure used internationally.)
Vehicle manufacturers 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 week
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.
