Need New Drums

The measurement of a drum diameter is done to the inside diameter of the drum — the braking surface. Measuring from the shoes is approximate at best, since it depends on wear. However, it is probably close enough to tell the difference between 10 and 11 inches — there are no 1/2-inch sizes.

The width measurement, however, refers to the width of the shoe, NOT the width of the drum. A lot of people get confused by this.

The idea is that the combined measurements (indirectly) describe the brake swept area — circumference X width.