Ford 1999 Wagon-Econoline Owner's Manual page 167

Temperature A B C
The temperature grades are A (the highest), B, and C, representing the
tire's resistance to the generation of heat and its ability to dissipate heat
when tested under controlled conditions on a specified indoor laboratory
test wheel. Sustained high temperature can cause the material of the tire
to degenerate and reduce tire life, and excessive temperature can lead to
sudden tire failure. The grade C corresponds to a level of performance
which all passenger car tires must meet under the Federal Motor Vehicle
Safety Standard No. 109. Grades B and A represent higher levels of
performance on the laboratory test wheel than the minimum required by
law.
The temperature grade for this tire is established for a tire that
is properly inflated and not overloaded. Excessive speed,
underinflation, or excessive loading, either separately or in
combination, can cause heat buildup and possible tire failure.
SERVICING YOUR TIRES
Checking the tire pressure
• Use an accurate tire pressure gauge.
• Check the tire pressure when tires are cold, after the vehicle has been
parked for at least one hour or has been driven less than 5 km
(3 miles).
• Adjust tire pressure to recommended specifications found on the Tire
Pressure Label.
Improperly inflated tires can affect vehicle handling and can fail
suddenly, possibly resulting in loss of vehicle control.
Tire rotation
Because your vehicle's tires perform different jobs, they often wear
differently. To make sure your tires wear evenly and last longer, rotate
them as indicated in the maintenance guide and or service guide. If you
notice that the tires wear unevenly, have them checked.
The following procedure applies to vehicles equipped with single rear
wheels, if your vehicle is equipped with dual rear wheels it is
recommended that only the front wheels be rotated (side to side).
Maintenance and care
167