Tire size is different from rim size since a single tire size fits on a variety of rim sizes. Tire sizes are marked as a range of the narrowest to the widest rim width on which they can be mounted.
Tire width changes in relation to the rim width on which it is mounted. A tire mounted on a narrow rim has a narrower width than when mounted on a wider rim. For proper performance, tire width should range between 1.45 and 2.0 times the inner rim width. Mounting too narrow tires on a rim risks tire damage while too wide tires have less grip on the rim.