225/40R18 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:
| 225 | The tire width is 225mm. |
| 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. 225/40R18 tire can be mounted only to a 18″ rims. |
Best selling 225/40R18 tires
Fullway HP108 All-Season Passenger Car High Performance Radial Tire-225/40R18 225/40ZR18 225/40/18 225/40-18 92W Load Range XL 4-Ply BSW Black Side Wall UTQG 380AA
24% Off(as of December 11, 2023 18:38 GMT +00:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)
Lionhart LH-503 All- Season Radial Tire-225/40R18 92W
(as of December 11, 2023 18:38 GMT +00:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)
Lexani LXUHP-207 Performance Radial Tire - 225/40R18 92W
8% Off(as of December 11, 2023 18:38 GMT +00:00 - More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)
What is 225/40R18 tire size in inches?
Because the width of 225/40R18 tire is stated in millimeters and sidewall height in percentages, you have to make calculations to see what the true size of 225/40R18 is in inches. Luckily, we have made these calculations for you.In this table you can see size of 225/40R18 in inches, as well as few additional metrics:
| In inches | In millimeters | |
| Section Width | 8.9″ | 225mm |
| Sidewall height | 3.5″ | 90mm |
| Diameter / Height | 25.1″ | 637mm |
| Circumference | 78.8″ | 2002mm |
| Rim Diameter | 18″ | |
| Revolutions | 804 per mile | 500 per kilometer |
Recommended Rim Sizes for 225/40R18 Tires
For 225/40R18 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 225/40R18 to a too wide or too narrow rim. Here are the recommended rim sizes for 225/40R18 tire:
| Diameter | Width Range |
| 18″ | 7.5-9″ |
225/40R18 – Variations
When you look at the tire code on 225/40R18 tires, you may see there are additional numbers and letters after the code 225/40R18. These numbers and letters refer to speed rating and load index of the tire. 225/40R18 has at least following variations available on the markets:
225/40R18 88H 225/40R18 88V 225/40R18 88W 225/40R18 88Y 225/40R18 92H 225/40R18 92S 225/40R18 92T 225/40R18 92V 225/40R18 92W 225/40R18 92Y