It is probable that vehicle dynamic load rather than static load is the criterion of major damage to the road substructure, with the added effect of tire scrub (in slewing, braking and acceleration) as the cause of road surface damage. This dynamic loading is a function not merely of static load but also of the suspension characteristics of the vehicle, particularly unsprung mass, tire rate and friction. Experience has shown that the tire/road impact loads can be studied in two parts; as the initial impact and then as the subsequent decaying impacts of the resultant vibration. An appropriate way of picturing this is on the display of an analog computer, programmed with values of parameters relating to an idealized model of the vehicle single-wheel spring-mass system. Correlation of the results with high speed cine photography of the tire carcass deflection is also described. The studies described include both tractor and trailer of motor trucks and also single-unit motor buses and trucks. It is predicted that forward trends in suspension design will be generally towards systems giving low dynamic load changes on the road surface. These developments should provide a better ride for driver and load, and hand a secondary benefit on dynamic road loading.