What Is the Meaning of the Numbers on Tires?
On every set of tires manufactured, several numbers and letters are molded into the rubber of the sidewall. These numbers and letters represent specific and important design and construction traits of the tire. Each number and letter has its own meaning, and they are used to correctly identify the proper tire for a particular application. When purchasing new tires, it is helpful to understand what these numbers and letters mean.
Other People Are Reading
-
Width
-
Every tire manufactured has a set of numbers and letters molded into the sidewall that will look similar to this: 205/60R16-89Z. The first number denotes the tire's section width in millimeters across the tread, from one sidewall edge to the other. The bigger the number, the wider and taller the tire. Bigger numbers are usually found on performance vehicles or trucks.
Aspect
-
The second number--60 in this example--is separated from the first by a slash, and it refers to the tire's aspect ratio. This ratio is by determined by the height of the sidewall in relation to the section width. This number represents a percentage of the total section width, so a lower number will mean a shorter sidewall height, whereas a larger number will mean a taller sidewall height. A tire with a 60 after the first number has a sidewall 60 percent as tall as the tire is wide across its section.
-
Construction
-
The letter after the first two numbers represents the type of construction used in the tire. R is the most common letter, and it stands for "radial," which is the industry standard in passenger-car tires. Before radial construction, tires were most commonly "bias-ply." Bias-ply refers to a type of construction in which the inner cords strengthen the tire wrap all the way around the sidewalls and tread areas at a 45-degree angle. Radial tires use cords that wrap the tire at a 90-degree angle, reducing the distortion and bulging of bias-ply tires.
Diameter
-
The third number--for instance, 16, which appears after the construction letter--represents the diameter of the rim that the tire is intended to be mounted on. The tire must match the rim to fit correctly. Any time you change the rims to a different size, such as with aftermarket rims, you must change the tire rim diameter as well.
Loading
-
The last number in the series--89 in this example--represents the tire's load rating. The load rating is the maximum amount of weight the tire is meant to support by itself and not in conjunction with other tires mounted on the same vehicle. To determine what this number means, it must be looked up on a tire load-carrying capacity chart. To get the total load capacity for a set of four tires, multiply the tire's load rating by four.
Speed
-
The final letter, Z in our example, represents the speed rating of the tire. This shows the highest speed the tire is designed to be operated at for extended periods. The speed rating helps in choosing tires for performance applications; exceeding this rating can result in failure of the tire. After 1991, the speed rating is always the last letter in the series of numbers and letters on the sidewall.
-
References
Resources
- Photo Credit tire image by Orlando Florin Rosu from Fotolia.com
