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The aerodynamic effects of the pickup truck tailgate are examined in this paper. It is shown that the removal or the lowering of the tailgate increases the aerodynamic drag of a pickup truck, increases lift by up to sixty percent and increases the yawing moment. All these changes are negative and reduce vehicle performance, albeit, only by small amounts. This finding demonstrates that the commonly seen removal of tailgates to reduce aerodynamic drag is a public misconception that should be discouraged by manufacturers and by regulators.

Six-component aerodynamic force and moment data are compared from tests of four 1/10-scale truck models at four wind tunnels on the North American Continent. Each model was tested in both a standard and a fuel saver configuration. The differences observed between tunnels were consistent for each aerodynamic component regardless of truck or configuration. The zero-yaw drag coefficients from each of the four tunnels were within ± 4 percent of the mean coefficients. The coefficient magnitudes for the other aerodynamic components showed variations that were often many times larger than those for drag. The variations between the incremental coefficients for all six aerodynamic components were less than those found for the coefficient magnitudes. A qualified comparison was made between the average drag coefficient magnitudes from the wind tunnels and those available from some on-road coastdown tests of the full-scale vehicles.

Wind tunnel measurements on a rectangular vehicle-like shape and on two detailed, scale-model trucks have been employed to define the front and rear edge geometries that minimize aerodynamic drag. Optimum configurations are identified with sufficient detail for commercial vehicle design purposes. Comparisons of the model-scale measurements with limited measurements on a full-scale straight truck in a large wind tunnel support the interpretation of these test results.