305/30R21 Tires & Tire Size

305/30R21 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.
30 The aspect ratio of the tire is 30. 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.
21 Rim diameter for the tire. 305/30R21 tire can be mounted only to a 21″ rims.

Best selling 305/30R21 tires

What is 305/30R21 tire size in inches?

Because the width of 305/30R21 tire is stated in millimeters and sidewall height in percentages, you have to make calculations to see what the true size of 305/30R21 is in inches. Luckily, we have made these calculations for you.In this table you can see size of 305/30R21 in inches, as well as few additional metrics:

  In inches In millimeters
Section Width 12.0″ 305mm
Sidewall height 3.6″ 92mm
Diameter / Height 28.2″ 716mm
Circumference 88.6″ 2251mm
Rim Diameter  21″  
Revolutions  715 per mile  444 per kilometer

Recommended Rim Sizes for 305/30R21 Tires

For 305/30R21 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 305/30R21 to a too wide or too narrow rim. Here are the recommended rim sizes for 305/30R21 tire:

Diameter Width Range
21″ 10.5-11.5″

305/30R21 – Variations

When you look at the tire code on 305/30R21 tires, you may see there are additional numbers and letters after the code 305/30R21. These numbers and letters refer to speed rating and load index of the tire. 305/30R21 has at least following variations available on the markets:

305/30R21 104H 305/30R21 104V 305/30R21 104W