Tire rolling resistance, in isolation from vehicle rolling losses including dissipation in the suspension and effects of the road surface, is a weakness in present procedures as they relate to fuel economy and pollution level testing. Work by Funfsinn and Korst, based on coastdown experiments and computer simulation, has shown that substantial and measurable increases in rolling losses occur for rough road surfaces. The present investigation used vehicle axle accelerations to experimentally examine various road surfaces. Correlation with computer simulations allowed the development of a deterministic road roughness model which is used to predict energy dissipation in both the tire and suspension as functions of roughness, tire pressure, and speed. Application of the methodology to coastdown techniques and comparison to the experimental results of Funfsinn results in good agreement and confirms rolling loss increases of up to 20 percent compared to ideal smooth roads. The aerodynamic drag coefficient is also found to increase when driving on rough roads.