1993 Pontiac Grand Am Owner's Manual - Page 236

CAUTION Treadwear The treadwear grade is a comparative rating based on the wear rate the tire of The following information relates to the when tested under controlled conditions system developedby the United States on a specified government test course. National Highway Traffic Safety For example, a tire graded 1 0 would 5 Administration which grades tiresby wear one and a half (1%) times as well treadwear, traction and temperature on the government course as a tire performance. (This applies only to graded 100. The relative performance of vehicles sold in the United States.) tires depends upon the actual conditions of their use, however, andmay depart significantly from the norm due to variations in driving habits, service practices and differences road in I characteristics and climate. A Mixing tires could cause you to lose control while driving. If you mix tires of different sizes or types (radial and bias-belted tires), the vehiclemay not handle properly, and you could have a crash. Be sure to use the same size and type tires on all wheels. It's al right to drive with your compact l spare, though. It was developed for limited useon your vehicle. Grding 235 " '