Performance and cost-effectiveness of air disc brakes and air drum brakes for truck semi-trailers in different road and speed conditions

Ampadu, Vincent Michael; Alrejjal, Anas; Ksaibati, Khaled · 2023 · Crossref

DOI: 10.14254/jsdtl.2023.8-1.2

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Summary

This study investigates the performance and cost-effectiveness of air disc brakes (ADBs) versus air drum brakes for truck semi-trailers, specifically addressing safety concerns regarding brake failure on steep downgrades. The research is motivated by the increasing vulnerability of trucks to runaway crashes due to modern design enhancements—such as reduced aerodynamic drag and engine friction—that place greater thermal loads on braking systems. While drum brakes remain dominant in North America due to lower initial costs, disc brakes offer superior cooling and braking torque. The study aims to determine under which road and speed conditions disc brakes provide sufficient performance benefits to justify their higher upfront costs. The researchers utilized TruckSim™ 2020, a multibody vehicle dynamics simulation package, to model a fully loaded 80,000 lb five-axle tractor-semitrailer. The simulation compared braking performance across varying downgrades (3%, 6%, and 9%) and speeds (50, 60, 70, and 80 mph). Brake torque capacities were modeled based on experimental data, with disc brakes assigned a capacity of 10 kNm and drum brakes 7.5 kNm. Additionally, a life-cycle cost analysis was conducted using retail component costs, assuming disc brakes cost approximately 2.2 times more than drum brakes, and factoring in replacement intervals for brake pads (30,000–70,000 miles) versus brake shoes (15,000–30,000 miles). The results indicate that disc brakes consistently shorten braking distances by 10–20% compared to drum brakes. The percentage reduction in braking distance increases with steeper grades and higher speeds, ranging from 12% to 19%. Specifically, at 50 mph on a 3% grade, disc brakes reduced braking distance by 12%, whereas at 80 mph on a 9% grade, the reduction was 16%. The study found that braking distance increases linearly with speed and inversely with grade steepness. Economically, the life-cycle analysis suggests that trucking companies operating in steep terrain at high speeds can achieve long-term cost savings of 12–80% by using disc brakes, as the extended brake life offsets the higher initial purchase price. The significance of these findings lies in both operational efficiency and public safety. The study concludes that disc brakes are particularly cost-effective for fleets navigating mountainous terrain, where the risk of brake fade is highest. At a societal level, the improved braking performance of disc brakes is estimated to prevent rear-end collisions and runaway truck incidents, resulting in annual savings of at least $649 million. The authors suggest that these findings support the adoption of disc brakes in high-risk environments and may inform updates to the Grade Severity Rating System to allow for higher safe descent speeds.

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• braking response