A Method of Measuring the Cushioning Quality of Tires 270021

TIRES of high shock-absorbing capacity greatly reduce the blows delivered to roadways by heavy vehicles and the reactions on the vehicles; they also absorb most effectively the shocks in a vertical direction that are the cause of the greatest discomfort to passengers. With a view to making a laboratory study of these shock-absorbing properties of tires, an instrument called a bounce-recorder has been devised and is described. This instrument records the paths followed by tires in passing over obstacles placed in their way. From these records, the vertical acceleration of a tire at any point of its flight can be determined, the purpose of doing so being twofold, namely, to develop an accurate and fairly rapid means of ascertaining the relative shock-absorbing capacities of tires by the acceleration method and to find out whether load-deflection tests made on the Olsen testing-machine could be used for the same purpose.

The details of construction and method of operation of the bounce-recorder are described, the manner of analyzing the results of the tests is explained, and curves are plotted to visualize these results. Inasmuch as the tests showed that for all practical purposes the initial vertical acceleration is a fair indicator of the cushioning quality of a tire, a short method was adopted which was far less laborious than the double differentiation method originally used, yet was sufficiently accurate to classify tires in the order of their shock-absorbing capacities; this method is also explained. With regard to the relative value of static and dynamic tests as a means of determining the comparative shock-absorbing capacities of tires, the conclusion is reached that whenever any two tires designed for the same service and differing slightly in road quality are tested, the static and the dynamic tests always distinguish these capacities in the same order.