How to Read a Tire

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It's easy to read a tire once you know what all those numbers and letters stand for. (Photo: @askoldsb via Twenty20)
If you look at your car tires closely, you’ll notice that there are a lot of words, letters, and numbers on them. All of these characters give you information about your tires, which can help you understand their specifications and what they are capable of and best used for. They also help you (or a mechanic) match tires when you purchase new ones.
At first, these symbols are all very confusing. However, once you get to know what everything means, they’re actually quite simple and you’ll be able to read any tire out there.

How to Read the Outer Circle on a Tire

The outer circle, which is more prominent than the inner circle and bears the manufacturer and tire names, has the bulk of the tire information printed on it. The technical information is printed in larger font and starts with a letter, which is the service description. This is usually the letter P, which denotes a passenger vehicle. However, it may also be T (temporary, usually a spare tire), LT (light truck), or ST (special trailer).
Following the service description is a three-digit number, which is the tire width measured in millimeters. The width measures the size of the tire from the edge of each sidewall. The tire width is followed by a slash and then a two-digit number, which is the aspect ratio. The aspect ratio measures the sidewall height as a percentage of the tire width.
The tire size is followed by a letter, which represents the internal construction of the tire. This is almost always an R (radial), but in some trucks it may be a B (bias-ply). Following the internal construction is a number that represents the diameter of the wheel in inches.
Next comes the load index. The load index is represented by a number, which corresponds to a weight (you can find the weight on a load-carrying capacity tire chart, which may be in your owner’s manual). Multiply the weight marked by the load index by four, and you have the total weight the vehicle can safely carry.
The final symbol is the speed rating, represented by a single letter. The letter represents how fast the tires can safely be driven. The ratings are S (112 MPH), T (118 MPH), U (124 MPH), H (130 MPH), V (149 MPH), Z (more than 149 MPH), W (168 MPH), Y (186 MPH), and (Y) (more than 186 MPH).
The outer circle also features, in smaller font, the tire’s temperature, treadwear, and traction ratings.

How to Read the Inner Circle on a Tire

The inner circle of a tire doesn’t have much information. It features the U.S. Department of Transportation number, in case there are recalls, as well as the maximum air pressure, maximum load rating, and tire ply composition. However, there are no symbols or codes, so this information is more intuitive to read.
Learning to read your tires can help you fully understand what they’re capable of. The information may look like a bunch of nonsense letters and numbers, but tires are actually quite easy to read.