305/40R20 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:
| 305 | The tire width is 305mm. |
| 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. |
| 20 | Rim diameter for the tire. 305/40R20 tire can be mounted only to a 20″ rims. |
Best selling 305/40R20 tires
MICHELIN Pilot Sport A/S 3 All-Season Tire 305/40R20/XL 112V
13% Off(as of June 6, 2023 07:55 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.)
Set of 2 (TWO) Accelera Iota ST68 All-Season High Performance Radial Tires-295/40R20 295/40ZR20 295/40/20 295/40-20 110Y Load Range XL 4-Ply BSW Black Side Wall
(as of June 6, 2023 07:55 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.)
Pirelli Scorpion Verde All Season All-Season Radial Tire - 305/40R20 112V
19% Off(as of June 6, 2023 07:55 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 305/40R20 tire size in inches?
Because the width of 305/40R20 tire is stated in millimeters and sidewall height in percentages, you have to make calculations to see what the true size of 305/40R20 is in inches. Luckily, we have made these calculations for you.In this table you can see size of 305/40R20 in inches, as well as few additional metrics:
| In inches | In millimeters | |
| Section Width | 12.0″ | 305mm |
| Sidewall height | 4.8″ | 122mm |
| Diameter / Height | 29.6″ | 752mm |
| Circumference | 93.0″ | 2362mm |
| Rim Diameter | 20″ | |
| Revolutions | 681 per mile | 423 per kilometer |
Recommended Rim Sizes for 305/40R20 Tires
For 305/40R20 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 305/40R20 to a too wide or too narrow rim. Here are the recommended rim sizes for 305/40R20 tire:
| Diameter | Width Range |
| 20″ | 10-12″ |
305/40R20 – Variations
When you look at the tire code on 305/40R20 tires, you may see there are additional numbers and letters after the code 305/40R20. These numbers and letters refer to speed rating and load index of the tire. 305/40R20 has at least following variations available on the markets:
305/40R20 112V 305/40R20 112Y