Multi-axle steering systems with a tractor and up to three full trailers are studied with linear yaw plane models to investigate the effect of additional steering on off-tracking phenomena during 90-degree turns and on the lateral responses during lane-change manoeuvres. The dependence of critical speed(s) for lateral stability on the location(s) of steered trailer axle(s) is studied via a linear stability analysis. Addition of non-steered trailer(s) reduces the stability. However, trailer steering results in a drastic reduction of high- and low-speed off-tracking, lateral forces, and yaw and slip velocities and in the concomitant increase in directional stability.
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