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The aerodynamic drag of rolling vehicles was studied by towing pairs of side-by-side identical small-scale models in rolling contact with the bottom of a water-filled trough. An instrumented towbar measured the difference in the models' overall drag forces in order to determine the effect of changes in a model's configuration on its aerodynamic drag. The effects of wheel-rim covers, axle fairings, and wheel-housing volume on vehicle drag were studied with the test apparatus. The magnitude of the effects were well outside the range of experimental error, and correlated well with published results of similar studies performed in wind tunnels. Testing indicated that lift-induced changes in vehicle rolling resistance would not significantly alter results of tow testing under normal circumstances. Advantages of the underwater tow test include the ability to inexpensively simulate rotating wheels and to study the interaction between rotating wheels on a moving vehicle and the ground plane.