An apparatus for measuring aerodynamic properties of a wheeled vehicle within a wind tunnel, comprising: a plurality of moveable surfaces with each of the moveable surfaces in groundward contact with a respective wheel of the vehicle or a single moveable surface in groundward contact with all wheels of the vehicle and the moveable surface or surfaces supporting the weight of the vehicle that is disposed within the wind tunnel; a structure supporting the moveable surface or surfaces , with the moveable surface or surfaces being disposed within the wind tunnel; the moveable surface or surfaces being each disposed for synchronous motion thereof along a longitudinal direction of the wind tunnel for forward motion of the vehicle ; a controllable motor configured to move the moveable surface or surfaces ; a sensor configured to detect a longitudinal position of the vehicle relative to the structure while said vehicle is disposed for free longitudinal movement thereof with respect to the plurality of moveable surface or surfaces and the wind tunnel; a controller configured to direct motion of the motor in response to a position signal delivered from the sensor to maintain the vehicle stationary along the longitudinal direction while the vehicle is self-propelled; characterized by a device configured to measure power being delivered by the motor to move the moveable surface or surfaces ; whereby the apparatus is configured to determine a difference in power being delivered by the motor to move the moveable surface or surfaces between different combinations of vehicle operating speed and wind speed from the headwinds impinging on the vehicle being tested and to determine the power being dissipated by the vehicle in drag under various operating conditions. a plurality of moveable surfaces with each of the moveable surfaces in groundward contact with a respective wheel of the vehicle or a single moveable surface in groundward contact with all wheels of the vehicle and the moveable surface or surfaces supporting the weight of the vehicle that is disposed within the wind tunnel; a structure supporting the moveable surface or surfaces , with the moveable surface or surfaces being disposed within the wind tunnel; the moveable surface or surfaces being each disposed for synchronous motion thereof along a longitudinal direction of the wind tunnel for forward motion of the vehicle ; a controllable motor configured to move the moveable surface or surfaces ; a sensor configured to detect a longitudinal position of the vehicle relative to the structure while said vehicle is disposed for free longitudinal movement thereof with respect to the plurality of moveable surface or surfaces and the wind tunnel; a controller configured to direct motion of the motor in response to a position signal delivered from the sensor to maintain the vehicle stationary along the longitudinal direction while the vehicle is self-propelled; characterized by a device configured to measure power being delivered by the motor to move the moveable surface or surfaces ; whereby the apparatus is configured to determine a difference in power being delivered by the motor to move the moveable surface or surfaces between different combinations of vehicle operating speed and wind speed from the headwinds impinging on the vehicle being tested and to determine the power being dissipated by the vehicle in drag under various operating conditions. <EOS>