How to Read Tire Sizes

Reading Tire Sizes and Ratings

Knowing how to read tire sizes on your car’s tires is important, so you’ll know which tire size to buy the next time your vehicle requires new tires. Reading tire sizes might seem like reading Chinese if you don’t know what you’re looking at, but it’s actually pretty easy once you know how to read the tire size information. Each number or letter corresponds with particular information for your car, and this is standard throughout the industry.

Below is a guide for how to read tire sizes. I’ll first touch on the tire numbers you’ll need to learn how to read, then move on to the most common letters you’ll come across.

Reading the Numbers on Your Tire

You’ll see a tire number at the beginning of the sequence of numbers that is given as a slash. For instance, you might see something like 185 / 65 on a smaller tire size. Each of these numbers have to do with some aspect of the size of the tire. I’ll explain these two numbers below.

  1. Width of the Tire (Millimeters) – The number before the slash is the width of the tire. This is simply the width of the tire which actually touches the road, from one sidewall to the other sidewall. In the example above, the width of the tire would be 185 millimeters.
  2. Aspect Ratio – This gives the height of the tire’s sidewall as a percentage in comparison to the width of the tire. In the example above, the number is 65 and therefore the aspect ratio of the tire is 65%. This means that the sidewall’s height from the base of the tire to its inner radius is 65% of 185.
  3. Rim Size – This is the last number in the sequence, found after the letters which come after the aspect ratio. This is the rim size of the car you’ll be placing your tires on. It’s important to match the tires you’re buying with your car’s rim size. When you go into the tire store, the tire salesperson will ask what your rim size is. So be prepared to give this number when buying new tires.

Reading the Letters on Your Tires

How To Read Tire Sizes

  • R – Radial construction. The tire tread is designed to give it added strength. Found between aspect ratio number and the rim size number.
  • B – Belted tire construction. The tire tread is designed to give it a smoother ride and bet traction. Found between aspect ratio number and the rim size number.
  • D – Bias-ply tire construction. Designed to give a smoother ride on rougher terrain, though the trade off is weaker plies and therefore weaker treads. Found between aspect ratio number and the rim size number.
  • M + S – Mud and Snow. Means the tire is designed to ride on mud and snow (in the city) without trouble. Usually found before the numbers.
  • P – Passenger. This tire is made for passenger vehicles. Usually found before the numbers.

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