Two-Number System
All Type III tires use a two-number size numbering system. The first number indicates the nominal section width of the tire, while the second number refers to the nominal diameter of the wheel. Both measurements are in Inches
Example
Tire Size: 6.00-6
Nominal Section Width: 6 inches
Nominal Rim Diameter: 6 inches*
*In this example, the diameter of the tire is NOT included in the numbers but it would be approximately 17 inches.
Three-Number System
Some tires use the three-number system to indicate the size of the tire. The first number in this series is the nominal diameter of the tire.
Example
Tire Size: 15-6.00-6
Nominal Tire Diameter: 15 inches
Nominal Section Width: 6 inches
Nominal Rim Diameter: 6 inches
The correct tire size for your aircraft is determined by the aircraft manufacturer and is based on the weight load, landing, take-off speeds, and other factors. Alternate tires can also be approved for installation by S.T.C. (Supplemental Type Certificate)