Several parameters which affect the fuel consumption, performance, and top speed of a vehicle are vehicle weight, tire rolling resistance, aerodynamic drag and driveline configuration. Studies have indicated that it is possible to change each of these parameters to reduce the fuel consumption of a vehicle. However, the resulting performance characteristics must also be evaluated over the range of any changes. The purpose of this paper is to assess these vehicle design variables with respect to top speed, performance, and fuel economy.Six vehicles representative of 1978–1979 small, mid-size, and large automobiles and light duty trucks were selected for this study. By utilizing a vehicle simulation program the vehicles were run over the FTP urban and highway drive cycle schedule, and various performance schedules. The results are evaluated qualitatively and quantitatively with respect to the sensitivity of the dependent variables to changes in the independent variables. The most important factor when using the above changes in fuel economy and performance for a given vehicle change is to be cognizant of the range of vehicle design variables from which the performance and fuel economy changes were derived.