FORD 2013 F-550 v.3 - Manual (Page 347)

Treadwear
The treadwear grade is a comparative rating based on the wear rate of the
tire when tested under controlled conditions on a specified government
test course. For example, a tire graded 150 would wear 1
1 ⁄
2
times as well
on the government course as a tire graded 100. The relative performance
of tires depends upon the actual conditions of their use, however, and may
depart significantly from the norm due to variations in driving habits,
service practices, and differences in road characteristics and climate.
Traction AA A B C
WARNING: The traction grade assigned to this tire is based
on straight-ahead braking traction tests, and does not include
acceleration, cornering, hydroplaning or peak traction characteristics.
The traction grades, from highest to lowest are AA, A, B, and C.
The grades represent the tire’s ability to stop on wet pavement as
measured under controlled conditions on specified government test
surfaces of asphalt and concrete. A tire marked C may have poor
traction performance.
Temperature A B C
WARNING: 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.
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. 139. Grades B and A represent higher levels of
performance on the laboratory test wheel than the minimum required
by law.
346 Wheels and Tires
2013 F-250/350/450/550 (f23)
Owners Guide gf, 3rd Printing, December 2012
USA (fus)