Aerodynamic behavior of the vehicle changes dramatically when a vehicle is modified from a closed body to a convertible vehicle. Change in the flow behavior and its effect on the vehicle road load and consequently on the fuel economy have been studied systematically from a full vehicle closed model to a convertible vehicle model. The flow patterns and the flow velocities both inside and outside the vehicle are studied using commercial Computational Fluid Dynamics (CFD) solver Star CCM+.In this paper a modified cabriolet is analyzed and is compared with the closed roof production vehicle and the closed roof production vehicle with various windows open configurations. The vehicle drag coefficient and the air flow behavior inside the passenger cabin are compared. Theoretical calculations are also done to compare the changes in road load at different vehicle speeds. The result shows that the Cabriolet vehicle drag coefficient is about 32% higher than the closed roof production vehicle. Various design modifications like the wind deflector and wind barrier are attempted to improve the aerodynamic performance.