Citation

Dillard JH. Highw. Res. Board bull. 1962; 348: 36-43.

Copyright

(Copyright © 1962, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

The procedure for using a pendulum-type (tapley) decelerometer to measure the coefficient of friction is an empirical one in which the test car is braked for 1 sec and the maximum deceleration recorded by the device. The coefficient of friction determined in this way is reported to be close to the value obtained by measuring the stopping distance. The value of the method is that it converts any car into a friction-measuring device merely by placing the self-contained decelerometer on the front floorboard of the car. Also it does not require that the test vehicle be fully stopped, hence it can be used in all but heavy traffic. Its low cost is also a great asset. However, the relationship between the maximum deceleration during the first, second and the average coefficient obtained by measuring the stopping distance is an empirical one. Therefore, before any faith can be placed on the method when used on american cars whose suspension systems and other factors differ, the degree of correlation must be established. In 1960, stopping distance tests were run on 14 sites with 7 measurements per site. A movie camera recorded the action of a tapley decelerometer and the deceleration data have been reduced from these films. The paper presents the data from this study and attempts to show the extent to which the empirical 1-sec braking procedure agrees with the stopping distance results.