315/40R21 in Inches

A 315/40R21 tire has a 30.9-inch diameter, a 12.4-inch width, and is designed for a 21-inch rim.

In high flotation terms, this tire is labeled as 30.9x12.4R21.

315/40R21 Tire Size
12.4"
30.9"
315/40R21 Tire Size in Inches
315/40R21 Tire Circumference
97.1"
21"
5"
652.2 revs/mile

315/40R21 Tire Overview

Height
30.9 inches
Wheel Diameter
21 inches
Tire Width
12.4 inches
Circumference
97.1 inches
Sidewall Height
5 inches
Revolutions
652.2 per mile
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What does 315/40R21 mean?

315/40R21 tire size meaning in inches

315/40R21 is a tire size with the following dimensions:

  • 315 is the width of the tire in millimeters. This number also indicates the appropriate width of the rim on which the tire should be mounted.
  • 40 is the aspect ratio, which is the ratio of the tire's height to its width. This affects the tire's handling and ride comfort
  • R indicates the tire's construction type, meaning it has a radial construction. This provides stability and precision to the tire.
  • 21 is the diameter of the wheel in inches, on which the tire is to be mounted.

315/40R21 Tire Conversion

DimensionsInchesMillimeters
Tire Diameter30.9 in785.4 mm
Section Width12.4 in315 mm
Rim Height21 in533 mm
Sidewall Height5 in126 mm
Circumference97.1 in2467.4 mm
Revolutions652.2 revs/mile
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FAQ About 315/40R21 Tire

How tall is a 315/40R21 tire?

The height (or diameter) of a 315/40R21 tire is 30.9 inches

How wide is a 315/40R21 tire?

The width of a 315/40R21 tire is 315 mm, which is about 12.4 inches.

What size rim fits a 315/40R21 tire?

A 315/40R21 tire fits on a rim that is 21 inches in diameter.

What does the 40 in a 315/40R21 tire mean?

The 40 in a 315/40R21 tire refers to the aspect ratio, meaning the height of the tire's sidewall is 40% of its width.


Alternative Tire Sizes for 315/40R21

Typically, it's recommended to choose a tire with a diameter (height) within 3% of the original equipment manufacturer (OEM) tire size.

However, keep in mind that this is a general guideline and not an absolute rule.

Here are some tire sizes that are compatible with the 315/40R21:

Tire SizeDiameterRim
255/45R2130.0″ (-2.9%)21 x 9.5-11.0
255/50R2131.0″ (0.3%)21 x 7.0-9.0
265/45R2130.4″ (-1.6%)21 x 8.5-10.0
275/45R2130.7″ (-0.6%)21 x 8.5-10.5
275/50R2131.8″ (2.9%)21 x 7.5-9.5
285/40R2130.0″ (-2.9%)21 x 9.5-11.0
285/45R2131.1″ (0.6%)21 x 9.0-10.5
295/40R2130.3″ (-1.9%)21 x 10.0-11.5
325/40R2131.2″ (1.0%)21 x 11.0-13.0