Adapted from a Borrani brochure:
The rim incorporates a well which is required for fitting and removing the tire, as well as two side flanges to hold the beads. In general, the wheel has an asymmetric shape in order to make mre space available for the brake equipment.
The rim is marked by two dimensions which are expressed in inches, namely:
- Width (for example 4" or 4.00") measured between the vertical walls of the side flanges, and
- Nominal diameter, or fitting diameter, measured at the intersection of bead seats and the vertical walls of the side flanges where the angle is 5º.
A third specification of the rim is expressed as alphabetical letters (such as J, JK, K, and C) which correspond to profiles of the side flanges that are controlled by international standards.