How to Work Out Tire Size & Profile Width

All passenger vehicles in the United States utilize a sizing system that provides tire width, height and wheel diameter. The sizing system can be confusing because it uses a combination of millimeters, inches and implied percentages to represent the different tire specifications. Once you are familiar with each number in a tire size, you will be able to determine the width, height and wheel diameter for any tire.

Instructions

1. Locate the tire size. This is located on the sidewall of the tire and will look similar to 235/45R17.

2. Locate the width of the tire. In the case of our example, 235/45R17, 235 represents the width across the tire, in millimeters, from the widest point.

3. Calculate the sidewall height of the tire. In our example, 235/45R17, 45 represents the height of the tire’s sidewall, from rim to tread, as a percentage of the the tire width. This is also known as the tire’s series. The example tire has a sidewall height of 105.75 millimeters. To convert this to inches divide by 25.4. 105.75 millimeters divide by 25.4 equals 2.96 inches.

4. Locate the wheel diameter. This is the last number in the tire size. In our example, 235/45R17, 17 is the wheel diameter, in inches, that the tire is intended to be mounted on.

References

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