Vehicle temperatures depend on an interrelationship between the rate of engine heat rejection and vehicle speed. An experimental study was undertaken to compare power train component and underbody temperatures of a vehicle run on an outdoor proving ground with those of a vehicle run in a wind tunnel. The experiment was designed to isolate the effects of load and vehicle velocity. Based upon this study, wind tunnel and track results were found to be in close correlation when driveshaft horsepower was used as the correlation parameter. The under-vehicle airflow, as it relates to underbody temperatures and heat transfer, appears to be similar.