How to Measure Tire Rim Size

Automotive tires have four measurements to consider, while the wheels or rims they sit on have two. Rims are measured in diameter and width, according to the tires they fit. Tires are measured by section width, section height or profile, rim diameter and tread width. Tread width merely notes the spread of a tires tread as it meets the road, and doesn’t factor into rim size.

Difficulty: Moderately Easy

Instructions

1. Measure the rim width. This is noted in inches anywhere from 5 inches for small passenger cars, to 91/2 inches for trucks and trailers.

2. Measure the rim diameter. Take the diameter measurement from the inside groove that the tire bead sits on. It’s easiest to measure the inner diameter of the tire after it’s removed from the wheel. If you measure the outer diameter of the rim itself, it will be almost an inch larger than the specific size.

3. Measure the tire size by looking at the width, height and inner diameter of a tire. The size is written on the outer sidewall. P205/40R16 is a common tire size notation showing all these. The P indicates passenger car. The 205 is the width at the widest point between the sidewalls in millimeters. The 40 shows the height of the sidewalls from the inner diameter to the tread in millimeters. The R stands for radial and the 16 is the rim diameter in inches.

4. Match tires to rims. Select a rim with the diameter of the tire. Use manufacturer approved ratings to find an accommodating width. Tires are able to be mounted on rim widths that vary from 1 1/2 to 2 inches. Tire manufacturers specify approved width ranges.

Tips & Warnings

• Consider load ratings before finalizing a tire purchase.
• Never mount a tire on a rim with an unapproved width.