This report described a sequence of investigations whose aim was to understand why mechanically equalised multi axle trailer suspensions are ineffective when tested under road conditions. The mechanism of such suspensions was studied theoretically using: a) specific finite element analysis; b) an algebraic static model; c)a dynamic linear model; and d) dynamic non linear analysis. The objective was to find out what inherent design features there might be which led to lack of equalisation. The study revealed four possible reasons for poor equalisation: a) rotational stiffness of rubber equaliser bushes; b) damping moment associated with rotation of equaliser bushes; c) change in moment arm caused by movement of contact points between the springs and their bearing pads; and d) moment applied by friction forces to equaliser link. A working program was produced in which all the essential features of the suspension system were represented at a reasonable level of realism. This demonstrated that to achieve good equalisation under static conditions the following design features should be aimed at: a) freely rotating equaliser bearing; b) design of contact between spring and equaliser link must be such as to minimise the variation of moment arm of the spring end forces; and c) friction between spring and equaliser contact surfaces must be minimised.

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