Variability in Center of Gravity Height Measurement

A round-robin center of gravity height measurement study was conducted to assess current practice in the measurement of the vertical position of the center of gravity (c.g.) of light truck-type vehicles. The study was performed by UMTRI for the Motor Vehicle Manufacturers Association. The laboratories participating in the study were those of Chrysler Corporation, Ford Motor Company, General Motors Corporation, and the National Highway Traffic Safety Administration. The primary objectives of this study were (i) to determine to what extent the differing experimental procedures used by the participating laboratories at the time of the study result in significant differences in the measured vertical position of the center of mass of light truck-type vehicles, and (ii) to gain insight into the physical causes of such differences. The results of the program showed (i) there were significant differences between the c.g. height measurement results obtained by different laboratories, (ii) repeatability of results within the individual laboratories was generally good, and (iii) close examination of the individual procedures tended to explain the differences in results between laboratories. The study highlights the fact that c.g. height determination is not a simple matter. Subtle error sources abound, and different measurement procedures, each undertaken with great care, can produce significantly different results. Nevertheless, the results and observations suggest that, with appropriate improvements put in place, the participating laboratories might be expected to obtain very similar results.