Tires have a detailed code on the sidewall that provides details about the tire's construction and driving limits, per Edmunds.com. This information includes the type of tire, the width, the aspect ratio, the tire design and the wheel diameter.
The first letter on the side of the tire is often a "P," which stands for "passenger car," per Cars.com. A light truck tire usually shows "LT," while a commercial vehicle tire is often branded with "C." The first number on the sidewall is the tire width in millimeters. There is a slash after that number, followed by the aspect ratio, which provides the sidewall height as a percentage of the tire's width.
The number after the aspect ratio provides the tire design, which is almost always "R" for "radial," according to Edmunds.com. The radial design has been an industry standard for decades, but the bias-ply design, indicated with a "B" on the sidewall, is still occasionally used in some truck tires. The next number on the sidewall provides the wheel diameter in inches.
The number after the wheel diameter represents how much weight the tire is designed to hold, states Edmunds.com. A higher number means the tire is constructed to support more weight. The next letter indicates the tire's maximum speed. Additional ratings for traction, maximum tire temperature and treadwear are listed on the sidewall as well. A tire chart converts these ratings into actual numbers.