225/55R18 Tires & Tire Size

225/55R18 refers to the size of the tire. It’s a standard which is used by car and tire manufacturers. By having the standard, tire manufacturers are able to manufacture same size tires independently and users can buy same size tires from different manufacturers.

Here’s an explanation of what these metrics mean in practice:


225

The tire width is 225mm.

55

The aspect ratio of the tire is 55. Aspect ratio refers to the height of tire sidewall in relation to tire width in percentages.

R

The letter in the middle refers to tire construction. Practically all tires sold for cars are radials.

Sometimes you also see tires with RF or ZR. RF indicates the tire is run flat, whereas ZR means the tire has speed rating higher than V. These tires are also radials, as the R indicates.


18

Rim diameter for the tire. 225/55R18 tire can be mounted only to a 18″ rims.

What is 225/55R18 tire size in inches?

Because the width of 225/55R18 tire is stated in millimeters and sidewall height in percentages, you have to make calculations to see what the true size of 225/55R18 is in inches. Luckily, we have made these calculations for you.In this table you can see size of 225/55R18 in inches, as well as few additional metrics:

 

In inchesIn millimeters

Section Width

8.9″225mm

Sidewall height

4.9″124mm

Diameter / Height

27.7″705mm

Circumference

87.2″2214mm

Rim Diameter

 18″ 

Revolutions

 727 per mile 452 per kilometer

Recommended Rim Sizes for 225/55R18 Tires

For 225/55R18 tires you need to have correct size rims to install the tires to. There are different width rims available in the market, and you can run into problems by installing 225/55R18 to a too wide or too narrow rim. Here are the recommended rim sizes for 225/55R18 tire:

DiameterWidth Range
18″6-8″

225/55R18 – Variations

When you look at the tire code on 225/55R18 tires, you may see there are additional numbers and letters after the code 225/55R18. These numbers and letters refer to speed rating and load index of the tire. 225/55R18 has at least following variations available on the markets: