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6.4.4 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.
6.4.5 Steps for maintaining proper tire pressure
• Step 1: Locate the recommended tire pressure on the vehicle's tire information
placard, certification label, or in the owner's manual.
• Step 2: Record the tire pressure of all tires.
• Step 3: If the tire pressure is too high in any of the tires, slowly release air by
gently pressing on the tire valve stem with the edge of your tire gauge until you
get to the correct pressure.
• Step 4: If the tire pressure is too low, note the difference between the measured
tire pressure and the correct tire pressure. These "missing" pounds of pressure are
what you will need to add.
• Step 5: At a service station, add the missing pounds of air pressure to each tire
that is under-inflated.
• Step 6: Check all the tires to make sure they have the same air pressure (except
in cases in which the front and rear tires are supposed to have different amounts of
pressure).
If you have been driving your vehicle and think that a trailer tire is under-inflated,
fill it to the recommended cold inflation pressure indicated on your vehicle's tire
information placard or certification label. While your tire may still be slightly
under-inflated due to the extra pounds of pressure in the warm tire, it is safer
to drive with air pressure that is slightly lower than the vehicle manufacturer's
recommended cold inflation pressure than to drive with a significantly under-
inflated tire. Since this is a temporary fix, don't forget to recheck and adjust the
tire's pressure when you can obtain a cold reading.
6.4.6 Tire size
To maintain tire safety, purchase new tires that are the same size as the vehicle's
original tires or another size recommended by the manufacturer. Look at the
tire information placard, the owner's manual, or the sidewall of the tire you are
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