Buying tires online is easy once you can read your tire size. Every number you need is printed right on the sidewall of your current tires, and it takes about a minute to decode. Here is what each part means.

Where to find your tire size

Look at the outer sidewall of any tire on your car for a string like 205/55R16 91V. You can also find the recommended size on a sticker inside the driver's door jamb, or in your owner's manual.

What the numbers mean

Using 205/55R16 91V as an example:

• 205 is the tread width in millimeters.
• 55 is the aspect ratio: the sidewall height as a percentage of the width. A lower number means a shorter sidewall.
• R means radial construction, which is standard on almost every modern passenger tire.
• 16 is the rim diameter in inches, so this tire fits a 16-inch wheel.
• 91 is the load index, a code for how much weight the tire can carry.
• V is the speed rating, the maximum rated speed for the tire.

The three numbers that matter most for finding a fit are the first three: width, aspect ratio and rim diameter. In our example that is 205, 55 and 16.

Should all four tires match?

For the best handling and safety, keep the same size and, where possible, the same model on all four wheels. If you are replacing only two, put the newer tires on the rear axle.

Find your size on Treadfy

Once you have your three numbers, enter them in the size finder on our home page, or browse every tire we carry and filter by width, aspect ratio and rim. New tires, every size, low prices, with fast tracked shipping across the US.