235/40R18 Tires & Tire Size

235/40R18 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:

235 The tire width is 235mm.
40 The aspect ratio of the tire is 40. 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. 235/40R18 tire can be mounted only to a 18″ rims.

Best selling 235/40R18 tires

What is 235/40R18 tire size in inches?

Because the width of 235/40R18 tire is stated in millimeters and sidewall height in percentages, you have to make calculations to see what the true size of 235/40R18 is in inches. Luckily, we have made these calculations for you.In this table you can see size of 235/40R18 in inches, as well as few additional metrics:

  In inches In millimeters
Section Width 9.3″ 235mm
Sidewall height 3.7″ 94mm
Diameter / Height 25.4″ 645mm
Circumference 79.8″ 2027mm
Rim Diameter  18″  
Revolutions  794 per mile  493 per kilometer

Recommended Rim Sizes for 235/40R18 Tires

For 235/40R18 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 235/40R18 to a too wide or too narrow rim. Here are the recommended rim sizes for 235/40R18 tire:

Diameter Width Range
18″ 8-9.5″

235/40R18 – Variations

When you look at the tire code on 235/40R18 tires, you may see there are additional numbers and letters after the code 235/40R18. These numbers and letters refer to speed rating and load index of the tire. 235/40R18 has at least following variations available on the markets:

235/40R18 91H 235/40R18 91V 235/40R18 91W 235/40R18 91Y 235/40R18 95H 235/40R18 95T 235/40R18 95V 235/40R18 95W 235/40R18 95Y