Aerodynamic design for the new model Civic sought to reduce aerodynamic drag and help ensure vehicle stability at high speeds. Equivalent lift was employed as an evaluation index expressing the effect of aerodynamic forces on vehicle dynamic performance, and the importance of reducing rear equivalent lift in helping to ensure stability was verified in driving test measurements. In order to reconcile the reduction of rear equivalent lift with low drag, the control of longitudinal vortices at the rear of the vehicle was set as a goal, with measures adopted in both the platform and the exterior. The realization of increased underfloor flow velocity through the use of underfloor devices and the aerodynamic engineering of the exterior side-view profile and the area around the rear pillars reduced rear equivalent lift by approximately 50% against the previous model. This has limited changes in rear tire performance with changes in vehicle speed, and helped to ensure vehicle stability in the high-speed range.