1994 Chevrolet Astro 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 TrafficSafety 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 of the rate 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 thegovernment course as a tire graded 100. The relative performance of tires depends upon the actualconditions of their use, however, and may depart significantly from the normdue 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 pavementas 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. 6-51