How to Measure Tire Rim Size

by Jonra Springs
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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 tire's tread as it meets the road, and doesn’t factor into rim size.

Step 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.

Step 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.

Step 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" signifies ratio of height to width (aspect ratio), also known as profile or series. The "R" stands for radial and the "16" is the rim diameter in inches.

Step 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.

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