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This paper discusses wet stopping performance and stability 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 6×4 conventional truck tractors without modification to the control, application, or ABS systems. The foundation brakes compared include standard S-cam drum brakes on all six positions, two hybrid configurations (high-output S-cam drum and then air disc brakes on the steer axles), and air disc brakes on all six brake positions. The truck tractors were tested in two weight configurations, LLVW and GVWR using an unbraked control semitrailer. Analytical analyses of wet brake-in-curve testing indicate that the hybrid brake systems (employing higher-torque brakes on the steer axle only) might degrade brake-incurve performance. This disadvantage appeared to exist for both load conditions.