The Brake Debate: Discs vs drums on semi-trailers. And the winner is?
Drum or disc brakes for semi-trailers? UK-based transport operators are still polarised about which is best so one of Europe’s leading automotive engineering consultancies, HORIBA MIRA, was tasked with determining how each performed under identical conditions, and their results are in.
In the world of commercial transport, the choice of braking systems is a critical decision that affects safety, maintenance costs, and overall operational efficiency. For semi-trailers, the discussion comparing disc brakes and drum brakes continues to be a topic of significant interest. Both systems have their supporters and each has its own advantages, but recent technological advances and industry trends suggest a shift towards disc brakes.
To explore this further, SAF-HOLLAND, which manufactures both disc and drum brake systems, teamed up with logistics and transport specialists, WH Malcolm, to facilitate the forensic testing of the systems, side-by-side. Under the strict watch of unbiased, independent experts, their aim was to generate data to help fleet operators and transport engineers make better informed decisions on which system to specify.
SAF-HOLLAND and WH Malcolm engaged the services of HORIBA MIRA, the world-renowned vehicle engineering, test and development consultancy, to conduct impartial scientific trials to ascertain the difference in performance of trailers fitted with drum and disc brakes. To determine the performance differences, two identical trailers were commissioned by WH Malcolm Logistics, with the only difference being that one was equipped with disc brakes and the other fitted with drum brakes.
The trailer and tractor combinations were loaded with a gross mass of 24,000kg and using the trailer brakes only, the braking systems on both trailers were bedded and conditioned by conducting a series of stops, while the brake temperature rise up and cooling were closely monitored.
Again, for the actual tests, only the trailer brakes were used, without any influence from the tractor unit braking system and the ABS/EBS system was disconnected. The trailer brakes were applied by pressure in the service line via an independent tank/valve set-up triggered by an actuator located within the tractor unit.
The tests conducted included repeated brake applications at 1.5-mile intervals from 80km/h, recovery from water immersion from 50km/h and temperature sensitivity tests from 80km/h.
The results make for interesting reading and present a compelling case for the use of disc brakes over drum. Even when operating at higher working temperatures, a trailer equipped with disc brakes will consistently stop within a significantly shorter distance compared with drum brakes. A further 31.7 metres was needed by the drum brake equipped trailer to come to a complete stop.
Andy Dyer, Manging Director of SAF-HOLLAND UK commented: “These results give a clear indication of how disc brakes outperform drums, and perhaps explain why 85% of trailers operating in mainland Europe are fitted with disc brakes - they outperform drum in almost every way. Most importantly, discs will stop a semi-trailer within a distance that’s nearly eight car lengths shorter than a drum-braked equivalent. So, when specifying disc brakes operators are contributing to improving UK road safety – surely there cannot be a better reason.”
WH Malcolm’s Chief Fleet Engineer, Gavin Summers added, “We have been a leader in transport and logistics for over a century and we’ve held that position partly as a result of being early adopters of technological advances, although we’ve always insisted on rigorous testing of any new technologies. That’s why we felt that it was important to run these new tests putting drum brakes up against the latest generation of discs. We would then base decisions concerning the specification of braking systems upon current data provided by an unprejudiced and trusted source. HORIBA MIRA’s results are clear – disc brakes will stop a trailer quicker and more consistently than drums.”
The tests were conducted at HORIBA MIRA’s Nuneaton Technology Park in the spring of 2024 and were captured on film, which can be seen at www.saf-holland.co.uk