as part of a research programme being carried out in the laboratory to quantify the relationships between road unevenness and riding comfort, the level of loading applied to the road structure, and vehicle handling and control, the relationship between subjective assessment of ride and an objective measure of ride has been investigated. the objective measure of ride is defined to be the root-mean-square of the vertical acceleration at the person-seat interface in a moving vehicle. this report describes an experiment designed to examine the repeatability of the objective measure of ride and the variability of its subjective assessments. the results of the experiment show that: (i) the repeatability of the objective measure of ride is constant over the range of accelerations examined and it is unlikely to exceed 0.004 g. this level of repeatability is considered to provide adequate discrimination between road surfaces for the purposes of studies of riding comfort. (ii) the relationship between subjective assessments of ride and the objective measure of ride can be quantified in the form of a 'comfort characteristics curve'. this curve gives the probability that a given quality of ride will be rated as 'acceptable' or better by vehicle occupants. (iii) the level of the objective measure of ride increases linearly with speed; the level depends on vehicle type and on the unevenness of the road profile.(a)

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