For example, a tire rating might read P235/70R15 102S. Each group of numbers and letters describes a specific characteristic of the tire.
The first code, P235, refers to the width of the tire in millimeters. The letter indicates P for Passenger Car; another common letter code is LT for Light Trucks.
After the slash, the next two digits indicate the ratio of the tire's sidewall to its width; in the example above, the sidewall is 70 percent of the tire's width, or 164.5 millimeters. The R indicates a Radial tire, and the 15 indicates the wheel diameter in inches.
Load and Speed Codes
The final code indicates the load capacity of each tire, in this case 102 equating to 1,874 pounds per tire, and the maximum speed the tires are rated for, S indicating a top speed of 112 miles per hour.
The Good News
In most cases, you can simply use the make and model of your car to look up the proper tires for your vehicle.
Buying tires can be a complex process. You want to be sure to get the right tires for your vehicle, but deciphering the ratings can be difficult without a primer.