Chevrolet 1994 Astro Passenger Owner's Manual page 269

If you ever replace your tires with those not having a TPC Spec number,
make sure they are the same size, load range, speed rating and construction
type (bias, bias-belted
or
radial) as your original tires.
_ 1
-
.. .
Uniform Tire Quality Grading
The following information relates to the system developed by the United
States National Highway Traffic Safety Administration which grades tires
by treadwear, traction and temperature performance. (This applies only to
vehicles sold in the United States.)
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 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,
however, and may depart significantly from the norm due to variations in
driving habits, service practices and differences in road characteristics and
climate.
Traction
-
A, 8, C
The traction grades, from highest to lowest are: A, B, and C. 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 (turning)
traction.
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