A tire’s size is based on how it fits into the tire’s diameter.
To calculate a tire’s fit into your wheel, you subtract one inch from the diameter.
For example, a 1-inch tire would fit into a 5-inch wheel.
That’s because the diameter of a tire is based upon its width.
To find the tire size, you divide the tire diameter by the width of the tire.
This is how the tire fits into a wheel.