When you go to the tire shop to get your tires changed, have you ever wondered how installers know which tire best fits your car? If you want to learn what they know, but you don’t, you have come to the right place.

If you look closer at your tire, you will notice a series of letters and numbers. These markings specify the characteristics of your tire.

What Do the Numbers on a Tire Size Mean?

Vehicle Type indicates what class of tire it is. For example, “P” stands for passenger car tire, “LT” for light truck tire, and ST for special trailer.

Tire Width is also referred to as section width. 3-digit numbers after the letter represent the width of the tire in millimeters.

Aspect Ratio is the percentage of the tire’s height off the rim divided by its width. A lower aspect ratio is a sign of advantages for vehicle handling performance.

Construction denotes whether your car’s tires’ internal construction is radial or diagonal (bias ply). R stands for radial tires where plies run perpendicular to the centerline. D or B is for diagonal or bias ply where plies are aligned at diagonal angles such as 30-45°.

The Rim Diameter is marked on the tire in inches. This specification is important because it determines the compatible wheel size.

Load Index represents how much weight a single tire can support when fully inflated. The chart below indicates the corresponding weights of indexes in terms of pounds. As an example, a tire with an index of 94 can support up to 1477 lbs.

Speed Rating is a sign of the maximum velocity a tire can handle. For instance, a tire with a speed index of “R” is designed for speeds up to 170 km/h, while a “P” rated tire is limited to 150 km/h.

Engineers determine which tires are the best choice for their automobiles based on the vehicle’s design, performance needs, and safety configurations. When you go to a tire installer, they already know which tire they must install based on their relationships with automobile brands.

How to Read Tire Size?

Understanding Tire Size: A Step-by-Step Guide

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