View Here : Tire Numbers Meaning
Example: 205/55 R16 91W. The numbers in the tire size refers to different parts of the tire. The first number (205) identifies the section width, or the cross section, in millimeters. Typically following the section width is the sidewall aspect ratio or profile (55).
Tire Size Numbers. The size of our sample tire is 235/55R19. 235 – 235 is the width of the tire in millimeters. A 235mm width translates into 9.25 inches. 55 – 55 is the ratio of the tire’s height vs. width. The height of the tire is 55% of its width, which gives our sample tire a height of just over 5 inches.