1: If a "x" separates the 1st 2 sets of numbers the 1st number is the overall diameter of the tire. The 2nd number is the overall width. The last number represents the tire diameter.
2: Used for smaller and industrial tires. If a "/" separates the 1st 2 sets of numbers the 1st number is the overall width of the tire. The 2nd number identifies the section height. This is the measurement from the crown to the bead of the tire. The last number is the rim diameter. The overall diameter of the tire is D + D + C. So for a 4.10/3.50-4 tire the overall diameter is 11" (3.5 + 3.5 + 4).
Note that all measurements should be made when the tire is inflated to its recommended air pressure.
