Chevrolet Spark EV 2014 Owner's Manual page 285

nominal rim diameters of
10 to 12 inches (25 to 30 cm),
or to some limited-production
tires.
While the tires available on
General Motors passenger cars
and light trucks may vary with
respect to these grades, they
must also conform to federal
safety requirements and
additional General Motors Tire
Performance Criteria (TPC)
standards.
All Passenger Car Tires Must
Conform to Federal Safety
Requirements In Addition To
These Grades.
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 (1½) 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.
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.
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 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.