315/40R21 tires have a diameter of 30.9", a section width of 12.4", and a wheel diameter of 21". The circumference is 97.1" and the revolutions per mile are 653. Specs may vary by manufacturer. learn more
When searching for the perfect tire for your vehicle you need options. Click the "Alternate Sizes" button to see a list of similar tire sizes. You can then change the wheel size to see alternate sizes on a different diameter wheel.