By establishing the directions of application and abutment shoe force vectors in a systematic way, heavy-duty internal shoe brake performance can be optimized in one of two ways. Specific output (torque output for a given input) or, alternatively but not coincidentally, stability as well as lining and drum life can be maximized. The degree to which these ends can be achieved varies considerably with the basic type of brake and its design details. Understanding the distinction between equal force and equal displacement shoe expanders is essential when evaluating brake characteristics. In addition, it is important to consider that brake shoe and drum members are less than infinitely rigid when analyzing the effects of shoe force systems on brake parameters.