325/40R21 In Inches – Tire Size & Wheel Fitment Guide

What size tire is 325/40R21 in Inches?

The 325/40R21 tire has an overall diameter of 31.2 inches, a section width of 12.8 inches, and can be mounted on 21 x 11.0-13.0 inches rim. The equivalent tire size in the high flotation system is 31.2x12.8R21.

	Inches	Millimeters
Tire Diameter	31.2	793.4
Section Width	12.8	325
Rim Height	21	533
Sidewall Height	5.1	130
Circumference	98.1	2492.5

12.8"

31.2"

98.1"

21"

5.1"

645.7 Revs/Mile

To easy understanding, let us break down each component of the 325/40R21 tire size to know what these numbers represent and how they may affect your vehicle's performance:

How tall is a 325/40R21 tire?

The 325/40R21 tire has a width of 12.8 inches (325 mm). This is the measurement at its thickest point, the distance between the outer sidewall and the inner sidewall’s widest point, also called as tread width or section width.

How wide is a 325/40R21 tire?

The 325/40R21 tire has a height of 31.2 inches (793.4 mm). This is the measurement from the bottom to the highest point at the top of a tire through its exact center when inflated and unloaded.

325/40R21 sidewall height

The 325/40R21 has a sidewall height of 5.1 inches (130 mm). It’s measured from the rim to the outer edge of the tire's tread, expressed as a percentage of tire width.

What size rim do you need for 325/40R21 tire?

You can mount the 325/40R21 tire on a rim with a height of 21 inches and a rim width ranging from 11.0-13.0 inches. (Based on recommendations of The Tire and Rim Association (TRA))

Putting very narrow tires on wide rims or vice versa can result in reduced performance of the tire.

325/40R21 circumference

The 325/40R21 tire has a circumference of 98.1 inches (2492.5 mm), This is the measurement of the distance the tire travels in one revolution.

The tire circumference plays a crucial role in your vehicle's overall performance, affecting its speedometer acceleration, accuracy and fuel efficiency.

325/40R21 Revolutions

The 325/40R21 performs 645.7 revs/mile. Revolutions per mile indicate the number of times a tire rotates while it covers the distance of one mile.

Replacement Tire Sizes for 325/40R21

As a rule, you can replace the tire within a 3% difference in tire diameter (height) of the OEM tire size. However, it should be considered as a general guideline, not a hard and fast rule. Here is a list of compatible tire sizes for 325/40R21: