How to Determine Tire Size in Inches

Tires are labeled with a mixture of letters and numbers.

The typical tire size used in the automotive industry is a mixture of millimeters, inches and ratios. Take the typical tire size of 235/70R16, for example. The "235" represents the width of the tire in millimeters, followed by the "aspect ratio" of 70 and finally the wheel size, which is 16 inches. If a taller or wider tire is needed, using this type of numerical mixture can prove to be rather difficult. The easiest method to determine the height and width of a tire is to convert everything to inches.

Instructions

1. Calculate the width of the tire in inches. Multiply the width by 0.03937. For a tire that is 235 mm wide, multiply 235 by 0.03937, which equals about 9.25 inches.

2. Calculate the tire's sidewall height by multiplying the tire's width by its aspect ratio--the ratio of a tire's sidewall height to its width. If the aspect ratio is 70 and the width is 9.25 inches, multiple 0.70 by 9.25, which equals 6.475, or a sidewall height of about 6.5 inches.

3. Calculate the tire's height by adding the sidewall height twice and the wheel size. If the sidewall height is 6.5 inches and the wheel size is 16 inches, the equation would be 6.5 plus 6.5 plus 16 inches, which equals a tire height of 29 inches.

Tips & Warnings

• Changing the aspect ratio will change the overall tire height; decreasing the aspect ratio results in a lower-profile tire.

References

• Consumer Reports: Tire Features