How to Read a Tire Sidewall: Size, Load Index, Speed Rating

Start with the size

The most useful marking on a tire is the size. Take the example P265/55R18. Each part has a meaning.

The letter at the start shows the type of tire. P is passenger, LT is light truck, T is a temporary spare and ST is a special trailer tire. Some sizes have no prefix at all.

The first number is the section width in millimeters. In 265/55R18 the tire is 265 mm wide.

The second number is the aspect ratio. It is the sidewall height written as a percentage of the width, so 55 means the sidewall is 55 percent as tall as the tire is wide.

The letter R means radial construction. The last number is the wheel diameter in inches, so 18 means the tire fits an 18-inch wheel.

Sizes on this site follow the same pattern. The page for 225/65R17 is a good example to read alongside your own tire.

Load index and speed rating

After the size you will usually find a number and a letter, such as 91V in the size 205/55R16 91V. Together they are called the service description.

The number is the load index. It is a code, not a weight.

You look the code up in a chart to find the maximum load a tire can carry at its maximum inflation pressure. A load index of 91 corresponds to 1,356 pounds (615 kg) per tire.

The letter is the speed rating. It shows the speed the tire was tested for under set conditions. For example, H corresponds to 130 mph and V to 149 mph.

Do not treat the speed rating as a safe driving speed. Road conditions, weather and the state of the vehicle all matter.

Our guide to load index and speed rating covers both in more detail, including why you should never go below the number your vehicle maker specifies.

The DOT code

Look for the letters DOT on the sidewall. The marking certifies that the manufacturer states the tire meets U.S. Department of Transportation safety standards.

After DOT comes the tire identification number. For new tires it has 13 symbols.

The last four are the date code, which gives the week and year the tire was made. A code ending in 2225 means the 22nd week of 2025.

The full code is required on one sidewall only. If you cannot find it on the outside, check the inner side of the tire. Our guide to the tire date code shows how to read it step by step.

UTQG grades

Many passenger tires also carry three quality grades: treadwear, traction and temperature. They are molded into the sidewall between the widest part of the tire and the shoulder.

Treadwear is a number such as 400. Traction is a letter grade from AA to C. Temperature is a letter grade from A to C.

These grades come from the tire maker, and they are easy to over-read. See our guide to UTQG ratings for what they do and do not tell you.

Pressure and other safety markings

Federal rules for light vehicle tires also require the tire's maximum permissible inflation pressure and maximum load rating to be molded into the sidewall. They also require markings such as "tubeless" and "radial" and the number of plies in the sidewall and under the tread.

The maximum pressure is a limit for the tire. It is not the pressure to inflate to. The recommended pressure for your vehicle is on a label on the driver's door or in the owner's manual.

Snow markings

You may see M+S on the sidewall. It stands for mud and snow and is based on tread design. The performance of M+S marked tires is not defined or measured by that marking.

A symbol of a mountain with three peaks and a snowflake means the tire passed a standardized snow traction test. Our guide to all-season, all-weather and winter tires explains the difference.

Putting it together: an example

Here is how the pieces line up on one tire, using the example sizes from this guide.

Read 205/55R16 91V from left to right. The tire is 205 mm wide. Its sidewall is 55 percent as tall as it is wide.

It has radial construction and fits a 16-inch wheel. The load index is 91, which corresponds to 1,356 pounds per tire, and the speed rating is V, which corresponds to 149 mph.

Somewhere near that, you will find DOT and the identification number. Its last four digits give the week and year of manufacture. You may also find the UTQG grades, M+S, the maximum pressure and the other required markings.

Tire makers also print the brand name, the product name and a safety warning on the sidewall. These help you identify the exact tire but do not change the size.

What the sidewall does not tell you

The sidewall describes the tire. It does not tell you whether the tire suits your vehicle.

That is set by the vehicle maker. The door placard and the owner's manual show the specification, and the sidewall of the tires now on your vehicle may or may not match it.

Treat the sidewall as one source and the placard as another. If they differ, ask a tire professional rather than choosing for yourself.

Confirm the size before you buy

The sidewall of the tire now on your vehicle is one place to confirm the size. The placard on the driver's door is another. Your owner's manual lists the vehicle maker's specifications too.

If the tires on your vehicle are not the original size, the door placard shows what the vehicle maker specified. When the two differ, ask a tire professional which to follow.

When you have your size, use the tire finder to see tires and retailers for it. If you are thinking about a different size, the tire size calculator compares two sizes by diameter, sidewall height and speedometer difference.