1993 Pontiac Firebird Owner's Manual - Page 256

give proper endurance, handling, speed rating, traction, ride and other things during normal service on your vehicle. If your tires have an all-season treaddesign, the TPC number will be followed bya *'MS" mud and snow). (for If you ever replace your tireswith 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. 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 vehicle may not handle properly, and you could have a crash. Be sure to use the same size and type tires on all wheels. It's all right to drive with your compact spare, though. It was developed for limited use on your vehicle. 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.)