This research shows that an existing rear-wheel drive vehicle may be easily retrofitted with a continuously variable-transmission for the purposes of reducing the overall fuel consumption of the automobile. The retrofit-ability of this transmission is the primary advantage that it exhibits over other continuously variable-transmissions. By retrofitting this vehicle with the transmission components that are shown in this paper, the existing vehicle transmission continues to be used with the exception of the driveshaft which is replaced by the hydraulic continuously variable-transmission itself. Using a standard model for the vehicle dynamics, this paper presents a detailed analysis for the speed ratios of all gears, and shows how to specify the size of the hydraulic pump and motor to insure a safe pressure level of operation. To illustrate the usefulness of this method, an actual transmission is designed for the 1997 Ford Ranger, and the range of adjustability for the transmission is evaluated by seeking to hold the engine speed constant for a ramped speed output of the vehicle. In conclusion, this research shows that the design methodology is valid and that only minor errors in engine speed are observed during low ground velocities for the vehicle.