Section Width
The linear distance between the outside of the sidewalls of an inflated tire without any load on it (not including any sidewall decorations)

Aspect Ratio
This is also known as the Section Height. This is figured as a percentage of the section width. A tire size of 205/60R15 would have a section width of 205 millimeters and a section height of 60 percent of 205 millimeters.

Rim Width
The width between the flanges of the wheel (the part the bead of the tire touches)

Tire Size Calculator

Tire and Wheel Resizing

Tire Sidewall Characters

Tire Dimensions Explained

Tire Speed rating

Tire Components

Tire Tread Wear

Tire Wheel Size