many heavy lorries have closely spaced twin rear axles linked by a compensating arrangement designed to equilise the load distribution. in the past, dynamic load variations caused by different linked axle suspension systems have been shown experimentally to vary significantly and this report describes a theoretical investigation into some of the causes. two mathematical models of part-vehicles having axles linked by two common types of compensating arrangement are described. the dynamic loads applied to the road as the models pass over simple road surface irregularities are calculated. it is shown that the dynamic behaviour of the models is similar and that there is a range of speed (about 20-60 km/h for the particular cases considered) in which both models, when passed over a bump, apply significantly greater dynamic loads to the road than a model having an unlinked suspension. in this speed range therefore the linkages increase the potential of the vehicles to damage the road structure. the suspensions systems require adequate damping to minimise their response to road surface irregularities and it is shown that one model is inherently less well damped than the other, and that the dynamic loads applied to the road by both models can be significantly reduced by adding shock absorbers. it is also shown that reducing the tyre stiffness reduces the dynamic loads applied to the road by both models.(a).

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