Width: The first number in tire size indicates the section width. The section width is a measurement in millimeters across from the widest point of the outer sidewall to the widest point of the inner sidewall when mounted to a wheel.

Ratio: The second number in the size represents the aspect ratio of the tire. The aspect ratio represents the height of the tire as a percentage of the width. So a tire with an aspect ratio of 50 means the height of the tire is 50% of the width.

Diameter: The diameter indicates the diameter of the rim that the tire fits onto.