FIGURE 8 Approximate pad life as a function of the maximum disk pressure. (Courtesy of Twiflex Corp., Horseheads, NY.) FIGURE 9 Large calipers for disk brakes-model vs. referenced in Figure 8. (Courtesy of Twiflex Corp., Horseheads, NY.)

This was unintentionally demonstrated by a winch manufacturer between 1970 and 1980, as will be described later. Because of these observations we shall turn our attention to finding the ri that will produce the maximum torque before designing a face contact disk brake or clutch. Differentiation of equation (3-1) with respect to ri and setting the derivative to zero yields

(3-4)

as the theoretically optimum value of ri, corresponding to torque and activating force given by

(3-5)

and

(3-6)

for a single-face annular contact brake. Actual brake lining dimensions may differ somewhat from this inner radius because of concentric grooves in the

lining and/or experimental data which may imply an effective pressure distribution different from that given in equation (1-3).