The Effects of Foundation Brake Configuration on Class-8 Tractor Dry Stopping Performance 2004-01-2701

This paper discusses dry stopping performance comparisons of various foundation brake systems on Class-8 truck tractors (having a GVWR greater than 33,000 lbs.). For these studies, four configurations of foundation brakes were fitted to two modern 6x4 conventional truck tractors without modification to the control, application, or ABS systems. Foundation brakes compared include standard S-cam drum brakes on all six positions, high-output S-cam drum and then air disc brakes on the steer axles, and air disc brakes on all six brake positions. Discussions include analyses of stopping distance from 60 mph (96.6 kph) for all test conditions. The truck tractors were tested in two weight configurations, LLVW (i.e., bobtail) and GVWR (50,000 lbs. total axle weight, using an unbraked control semitrailer).

Analysis of Variance (ANOVA) tests indicate statistically different stopping distance means between all foundation brake configurations, whether the results for both weight configurations were combined or analyzed separately. Combining the results for both tractors, an “all disc brake” configuration could yield a 20% improvement in stopping distance (from 60 mph) at GVWR over the standard “all S-cam” brake configuration on dry pavement, and a 16% improvement at LLVW. With “hybrid disc” brakes, the improvements were 12% and 19% for GVWR and LLVW, respectively. For “hybrid drum” brakes, the improvements were 10% for both GVWR and LLVW.

Margins of compliance for the minimum stopping distances (versus a 30% reduction in current standards) are shown for each brake configuration. Also, statistically meaningful differences between various foundation brake configurations on two different truck tractors are shown and discussed in detail.