Hitch Position Sensitivity on Axle Loads and Braking Performance in Tractor-Trailers

The longitudinal dynamics during braking of articulated heavy vehicles is primarily governed by coupled load transfer mechanisms, yet the isolated influence of hitch location on axle load distribution and braking response remains insufficiently quantified. This study investigates the sensitivity of hitch height variation of a twin-axle tractor with a single-axle on the axle loads and consequently braking performance. A rigid-body longitudinal dynamics model is utilised and evaluated against a high-fidelity multibody simulation across a structured test matrix spanning friction levels and trailer loading conditions. Results show that hitch location primarily affects braking behaviour through redistribution of axle normal loads via hitch-induced pitching moments. A 400~mm increase in hitch height produces up to 5% variation in drive axle load in the unladen case, rising to approximately 16% under laden conditions. Longitudinal hitch variation yields comparable sensitivity in drive axle load, with increased influence on steer axle loading, while trailer axle load remains largely unaffected. Despite these variations, the overall braking metrics such as stopping distance and steady-state deceleration exhibit limited sensitivity to hitch location under most operating conditions. However, near friction limits, hitch-induced load redistribution significantly alters axle-wise friction utilisation and wheel lock sequence, steer axle-first at low deceleration and rear-axle-first at higher deceleration. The results demonstrate that while hitch location has a secondary effect on overall braking efficiency, it plays a critical role in stability-relevant behaviour mainly in the laden vehicle configurations. These findings highlight the importance of accounting for hitch-induced coupling in load-aware braking strategies for articulated vehicles.