The use of computer aided design tools has now proliferated to many areas of engineering and the use of robust and flexible design tools is paramount to modeling complex systems. Hybrid powertrains present often complex systems where simulation and modeling are important issues. This paper presents the development of a simulation tool for the modeling of hybrid powertrains for vehicular applications. The software is developed in Object Oriented code presenting a conceptually intuitive representation of real components. The importance of matching vehicle design against required drive-cycle is addressed, the various approaches for drive cycles discussed and methodology for making use of GPS data for vehicle simulation presented.