Hyundai sonata Owner's Manual page 496

Maintenance
Tread wear
The tread wear 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-a-half times (1½) 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.
These grades are molded on the
sidewalls of passenger vehicle tires.
The tires available as standard or
optional equipment on your vehicle
may vary with respect to grade.
Traction AA, A, B & C
The traction grades, from highest
to lowest, are AA, A, B and C. Those
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.
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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.
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. Grade C responds
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.
WARNING
The temperature grade for this
tire is established for a tire that
is properly inflated and not
overloaded. Excessive speed,
under-inflation, over-inflation, or
excessive loading, either separately
or in combination, can cause heat
build-up and possible sudden
tire failure. This may cause loss
of vehicle control resulting in an
accident.