The exact size, type and rating for a tire is listed on that tire's sidewall, according to Cars.com, and, as TireSafety.com notes, in the owner's manual. These are used to find an exact match or similar tires.
Once the size, dimensions and type of tires currently on a vehicle have been determined, it's easy to find comparable models and styles. Automotive professionals can recommend the optimal tire for seasonal weather conditions, including snow, rain and extreme heat, according to TireSafety.com.
Tires are also rated for their maximum speed, Cars.com notes. A Z rating, for example, denotes tires designed to handle the stresses associated with speeds in excess of 149 mph. Since these measurements and ratings are standard across the tire industry, it is possible to use them when searching for both new and used tires.
Regardless of their age, replacement tires should match the rim width of the current tires on a vehicle. Greater height or depth may still be possible, as long as the tire being used can fit over the existing rim. However, consult with an authorized tire dealer before buying tires of a different size or load index than the originals, or before mixing different types of tires, TireSafety.com cautions.