How to Calculate the Tire Size for 22.5" Rims

When increasing the size of the Original Equipment (OE) rim on a vehicle to a larger diameter, such as 22.5", it is crucial to obtain the correct size tire for the vehicle and new rim. To avoid having to recalibrate your new rim and tire combination, stay within a three percent deviation of the OE tire and rim diameter.

Things You'll Need

• Original Equipment Tire Size

Instructions

OE Tire Sizes

1. Read the OE tire size found on the sidewall of the tire. This will look similar to "265/65R18."

2. Note the width of the tire. In the previous example, 265 represents the width, in millimeters, from the widest point across the tire.

3. Calculate and notate the tire's sidewall height. For our example tire size, 265/65R18, 65 represents the height of the sidewall as a percentage of the tire width. Multiply 265 by .65 to get a tire height of 172.25 millimeters or 6.78 inches (1 millimeter = 0.03937 inches).

4. Note the OE rim diameter. In our example of 265/65R18, the last number, 18, is the rim diameter, represented in inches.

Calculating New Tire Sizes

1. Use the formula ((Width/25.4)xSidewall Percentage)x2 to calculate the OE tire height, in inches. The example of 265/65R18 would have an overall tire height of 13.56 inches. ((265/25.4)x65%)x2).

2. Calculate the final OE tire and rim diameter by combining the tire height and the rim diameter. The example 265/65R18 would add 13.56 to 18, resulting in a total diameter of 31.56 inches.

3. Using the three percent variance, you would want a new tire that, when combined with the 22.5" rim, has a diameter between 30.61 and 32.51 inches.

Tips & Warnings

• Ensure the width of the new tires also fit your vehicle properly.

References

• Tire Rack: Tire Size Guide
• Tire Rack: Calculating Tire Dimensions