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SERVICING AND MAINTENANCE 381
DEPARTMENT OF TRANSPORTATION
UNIFORM TIRE QUALITY GRADES
The following tire grading categories
were established by the National
Highway Traffic Safety Administration.
The specific grade rating assigned by the
tire's manufacturer in each category is
shown on the sidewall of the tires on
your vehicle.
All passenger vehicle tires must conform
to Federal safety requirements in
addition to these grades.
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 one and one-half 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 GRADES
The Traction grades, from highest to
lowest, are AA, A, B, and C. These 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 GRADES
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 vehicle 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.
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.
WARNING!
The temperature grade for this tire is
established for a tire that is properly inflated
and not overloaded. Excessive speed,
under-inflation, or excessive loading, either
separately or in combination, can cause heat
buildup and possible tire failure.
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21_WK_OM_EN_USC_t.book Page 381
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