Toyota 2012 Prius C Owner's Manual page 525

6-1. Specifications
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Treadwear
The treadwear grade is a comparative rating based on the wear
rate of the tire when tested under controlled conditions on a speci-
fied government test course.
For example, a tire graded 150 would wear one and a half (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. Performance may differ significantly from the norm due
to variations in driving habits, service practices and differences in
road characteristics and climate.
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Traction AA, A, B, C
The traction grades, from highest to lowest, are AA, A, B and C,
and they 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 braking
(straight ahead) traction tests and does not include cornering (turn-
ing) traction.
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