An articulated lorry was instrumented in order to measure its performance in straight-line braking. The trailer was fitted with two interchangeable tandem axle subchassis, one with an air suspension and the other with a steel monoleaf 4-spring suspension. The brakes were only applied to the trailer axles, which were fitted with anti-lock braking systems (ABS). The vehicle with the steel suspension was observed to have significantly worse braking performance than the air suspension, and also to generate larger vertical dynamic tire forces.Computer models were developed for the two suspensions, including their brakes and anti-lock systems. The models were found to reproduce most of the important features of the experimental results. It was concluded that the poor braking performance of the steel 4-spring suspension was mainly due to interaction between the ABS and load transfer effects, and that the vertical vibration caused by coupling between vertical and longitudinal forces was of secondary importance.