V. Stelmashchuk, S.Stelmashchuk Influence of effort in the traction and coupling on the stability of a light-tongue road train in the braking mode

Abstract

The braking of a light-duty road train is often complicated by additional forces transmitted through the traction-coupling device, which can trigger jackknifing and loss of lateral stability. Earlier studies have shown that, under nominal loading and when braking forces on all wheels equal the coupling forces, the road train remains stable across the full range of trailer masses at 25 m/s; at 30 m/s the critical trailer mass drops to about 2500 kg. Those models, however, did not account for two factors: timing asynchrony between the car's and trailer's braking systems, and the compression force in the traction-coupling device.
© Стельмащук В.В., Стельмащук С.В. 2026
ISSN 2313-5425 , 2026, №1 (26) 447
This work refines the planar braking model of a light-duty road train to include both effects and analyses the transient response to step braking at initial speeds of 15 m/s and 25 m/s.
The results show that during the first 0.3 s after braking begins, the normal road reactions on the car and trailer axles remain almost unchanged, because the compression force in the coupling absorbs part of the longitudinal load transfer. Over this interval the articulation angle stays below 0.015 rad and the trailer's lateral deviation does not cross the lane boundary (S_b = L_n · tan(0.015) = 0.029 m). With time, however, the articulation angle grows and the trailer drifts beyond the lane: S_b = 0.186 m at V = 15 m/s and S_b = 0.375 m at V = 25 m/s. The trailer's lateral oscillations are damped and its lateral velocity stabilises over time, so the road train eventually recovers stability.
The compression force in the traction-coupling device therefore proves a non-negligible factor within the first 0.3 s of braking and should be included in stability assessments of light-duty road trains.