Metric tire sizes are used to describe the dimensions of almost all passenger and light truck tires. While there are many variations of the metric tire size, they all share three main components: Section Width, Aspect Ratio, and Rim Diameter.
Section Width
The Section Width of a tire is the first number you will encounter in your metric tire size. It is a three digit number that measures the overall width of the tire at its widest point. Section width is measured in millimeters. There are 25.4 millimeters in an inch.
- 235/60R16 (Section Width = 235mm or 9.25")
- 275/35ZR18 (Section Width = 275mm or 10.82")
- LT245/75R16/E (Section Width = 245mm or 9.65")
For example, a 235/60R16 tire has a Section Width of 235. The tire is 235mm (or 9.25") wide at its widest.
Aspect Ratio
The Aspect Ratio is the second number you will encounter in your metric tire size. It is a two digit number (separated from the Section Width by a forward slash) that measures the sidewall height as a percentage of the Section Width.
- 235/60R16 (Aspect Ratio = 60%)
- 275/35ZR18 (Aspect Ratio = 35%)
- LT245/75R16/E (Aspect Ratio = 75%)
For example, a 235/60R16 tire has an Aspect Ratio of 60. The sidewalls are 60% as tall as the tire is wide (60% of 235mm = 141mm).
Rim Diameter
The Rim Diameter is the third number you will encounter in your metric tire size. It is separated from the Aspect Ratio by one or more letters. The Rim Diameter measures (in inches) the diameter of the rim on which the tire must be mounted.
- 235/60R16 (Rim Diameter = 16")
- 275/35ZR18 (Rim Diameter = 18")
- LT245/75R16/E (Rim Diameter = 16")
For example, a 235/60R16 tire has a Rim Diameter of 16 must be mounted on a 16" rim.
With the Section Width, Aspect Ratio, and Rim Diameter from your metric tire size, you can calculate every dimension of your metric tire.
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