The graphic above shows what each letter and number on the sidewall of a tire indicates.
The following is a breakdown of the components of the size of the tire.
Passenger car tire. If there is no P before the size it would indicate it is a European metric tire. An LT before the size would designate a light truck tire.
This is the Section Width in millimeters. This measurement is taken from sidewall to sidewall.
This number refers to the height of the sidewall, or the Aspect Ratio. It is a percentage of the section width. In this example, you would take 65 percent of 205 millimeters and this would give you the sidewall height.
Radial tire construction.
Wheel diameter in inches.