Front underbody dams and rear deck lips (“spoilers”) have been in use for some time as aerodynamic aids for automobile drag and lift reduction. However, the flow field effects and associated surface pressure changes which produce these improvements have not been well understood. A series of wind tunnel tests was performed with a 3/8-scale semi-detailed model of a notchback sedan. Force and moment measurements were augmented by model exterior, engine compartment and groundplane surface pressure measurements, as well as flow visualization experiments. Aerodynamic lift and drag contributions of various model components, as well as the changes produced on these components by the addition of “spoilers”, have been determined. Flow field mechanisms which will produce the observed pressure and force changes have been proposed.