This SAE Recommended Practice defines a clearance line for establishing dimensional compatibility between drum brakes and wheels with 19.5 in, 22.5 in, and 24.5 in diameter rims. Wheels designed for use with drum brakes may not be suitable for disc brake applications. The clearance line establishes the maximum envelope for brakes and minimum envelope for complete wheels to allow for interchangeability.
This document addresses the dimensional characteristics only, and makes no reference to the performance, operational dynamic deflections, or heat dissipation of the system. Valve clearances have not been included in the fitment lines. Bent valves may be required to clear brake drums. Disc brake applications may require additional running clearances beyond those provided by the minimum contour lines. Mounting systems as noted are referenced in SAE J694.