How to Determine Your Tire Size

There are many reasons why you may need the dimensions of your tires. Do you use a tape measure? Should you use the Metric or British/Imperial system?

Fortunately, there’s an easy and accurate way to get this information. Do you see the series of letters and numbers embossed on the sidewall of the tire? It’s not a product serial number or an obscure easter egg.

It’s actually a code that contains data about your tire such as the size, tire aspect ratio, and load rating. It’s also not difficult to decode.

Let’s use this series “P 215 / 60 R 15 93 T” as an example and start breaking down what it means.

1. The First Letter(s) Is the Service Type

The first letter or letters denote the type of service that the tire was designed for. In this case, the “P” stands for P-metric. This indicates that it’s meant for passenger vehicles.

“LT” means light truck, “C” equals commercial, while “T” stands for temporary spare. If you don’t see a letter before the first number, you have a Euro-metric tire that’s primarily used on European cars.

2. The First Three-Digit Number Is the Tire Width

The 3-digit number after the first letter is the width of the tread that’s in contact with the road. This is measured from sidewall to sidewall in millimeter units. In our example, the tire is 215 mm wide.

3. The Next Two-Digit Number Is the Tire Aspect Ratio

The aspect ratio is the ratio of the height of the sidewall (from the rim to the outside of the tread) to the tire width. It’s written in percentage form. It’s an important number if you’re considering downsizing your wheels.

In the example given, the number after the slash is 60. This means that the sidewall height is 60% of the tread width. Since we already know the width (215 mm), this means that the sidewall height is 0.60*215 or 129 mm.

4. The Next Letter Identifies the Tire Casing

The single letter following the aspect ratio reveals how the tire was constructed. In this case, the “R” means radial which means that the casing was built radially. “D” represents diagonal bias construction while “B” stands for belted bias.

5. The Next Two-Digit Number Is the Rim Diameter

If you’re getting new rims, this is the number to look for. The number after the letter in the middle designates the measurement of the rim diameter in inches. In our example, the rim diameter is 15 inches.

6. The Last Sequence Is the Tire Service Description

The last combination (a number followed by a letter) represents the load index and speed rating, respectively. The load index specifies the maximum load-carrying capacity of the tire. The speed rating gives you the maximum speed that the vehicle can handle.

Using the charts for load index and speed rating, we can see that the tire in our example is rated for 1433 lbs and can run safely at a maximum speed of 118mph.

Code Cracked!

Rather than giving vague numbers when shopping for new wheels, you can help the dealer find exactly what you’re looking for. Whether it’s the tread width or the tire aspect ratio, you’re confident that you’re giving accurate information.

This will help you with different tire issues, such as replacement or getting new rims, and makes things easier on you.

For more tips and tricks, feel free to check out our other articles about aftermarket wheels and other topics today.