How to Read Your Tire Size: The Basics

Deciphering your tire size can be difficult, but it doesn’t have to be. With a little bit of help, you’ll be on your way to understanding what those letters and numbers mean.

If you look at your tire’s sidewall, you’ll notice a series of numbers. Not sure what they mean? We’re here to explain. Those numbers are indicators of the size, type, and performance of the tire.

  • Tire Type. Every tire size features a letter at the beginning, for example, P. This tells us the type of tire.
  • Tire Width. This is the first 3 numbers after the letter, always the measurement in millimeters of the width of the tire.
  • Aspect Ratio. This refers to the ratio of the height of the tire's cross-section to its width. This number comes after the width and is separated by a slash. For example, in a size P215/65 R15 tire, the 65 means that the height is equal to 65% of the tire's width. The bigger the aspect ratio, the bigger the tire's sidewall will be.
  • Construction. This number follows the aspect ratio. The letter R, for example, means that it is a radial tire.
  • Wheel Diameter. Indicates the size of your vehicle’s wheel. A 15 means that your wheels are 15 inches in diameter.
  • Load Index. This number indicates the maximum load your tire can support when properly inflated. This will be the last number in the series.
  • Speed Rating. This is the final piece of information on your sidewall. This will tell you the maximum speed capability of your tire. Learn more about speed ratings here.

If this doesn’t help, feel free to give one of our locations a call. We have 11 locations across Airdrie, Strathmore, Cochrane, Okotoks, and High River, as well as surrounding areas of Calgary.

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