Coastdown Tests: Determining Road Loads Versus Drag Component Evaluation

Coastdown tests as presently evaluated for establishing dynamometer settings for road load simulation are satisfactory but cannot be utilized directly for extracting accurate information on aerodynamic vehicle drag. This is primarily due to the speed dependency of the tire rolling resistance, having linear and square term contributions which are not observable in the optimizing parameter evaluation procedure. A critical assessment of such effects is presented and the need for laboratory test results for tires is stated.