This SAE Recommended Practice defines a clearance line for establishing dimensional compatibility between drum brakes and 19.5 in, 22.5 in, and 24.5 in diameter wheels. Wheels designed for use with drum brakes may not be suitable for disc brake applications. The clearance line establisheds 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.
This SAE Recommended Practice currently defines clearance lines for establishing dimensional compatibility between drum brakes and 19.5, 22.5 and 24.5 in diameter wheels. The modification is to address the fact that not all current wheels used in drum brake applications may be suitable with disc brakes. Work is ongoing with other SAE committees to modify the clearance line to include disc brakes with the eventual objective of including disc brake wheel fitment into this document.