1. ABSTRACTThis paper describes the results of experiments carried out for modifying the characteristics of leaf springs with a view to improving ride comfort in leaf spring suspension vehicles.In this study, the factors contributing to the hysteresis loop of leaf springs, especially to the inclination in the transition zone of the hysteresis loop, were analyzed experimentally. The results of analysis were used in designing leaf springs with smaller inclination in the transition zone, and then the tests were carried out with these leaf springs.It is known that the dynamic spring characteristics of leaf springs is mainly related to the gradient of the diagonal of load-deflection hysteresis loop, that is diagonal spring rate. The diagonal spring rate is inversely proportional to the amplitude, of the deflection approximately and consequently, at very small amplitude, it reaches to the maximum inclination in this transition zone.Thereupon, the authors decided to study and analyze the behavior of the transition zone of the hysteresis loop, as the representation of dynamic spring characteristic under the very small deflection amplitude, and to find out the contributing factors on the dynamic spring rate.These findings can be summed up as follows. (1) At the transition zone of the hysteresis loop, the state of local elastic deformation is developed in the leaf end under the action of inter-leaf frictional force. (2) It is possible to set the dynamic spring characteristics, at a very small deflection, desirable value appropriately designing the local stiffness of the leaf end on the basis of eye diameter, leaf thicknes and leaf length.