This paper examines the results of steering controllability tests developed for objectively quantifying directional response.

The relationship of steering controllability characteristics, exhibited by subcompact, compact, and intermediate size automobiles produced in the U.S., to the specifications on yaw-rate gain and response time developed in research programs sponsored by the National Highway Traffic Safety Administration (NHTSA), is investigated through (1) an analytical survey of the yaw response of 1977 model year vehicles and (2) open- and closed-loop testing of three selected vehicles, in modified and unmodified conditions. With the exception of some vehicle models equipped with manual steering, the analytical survey and the open-loop tests show that the directional performance characteristics of 1977 subcompact, compact, and intermediate size cars lie within the "optimum" region that has been defined through NHTSA research. The closed-loop tests indicate that variations of yaw-rate gain of the magnitude studied may or may not be of consequence, depending upon the particular vehicle being studied.

After presenting these results, the paper gives conclusions and recommendations concerning specifications on yaw-rate gain and response time.