The paper proposes a method to analyze a trade-off between IC engine and electric battery sizes which is the essential issue of plugin hybrid and range extended electric vehicle design. This method implies a set of maps to be elaborated from batch simulations of hybrid vehicle running a driving cycle. Said maps establish relationships between ICE power, fuel consumption, electric energy consumption, and driving range of a vehicle. From these, one can choose a combination of ICE power and battery energy content meeting specific requirements for fuel economy and driving range. Mathematical model of the vehicle and the hybrid powertrain adopted for driving cycle simulations is described. Besides vehicle dynamics and drivetrain’s powerflows, it addresses battery’s current and voltage restrictions, which define performance of an electric drivetrain and have to be taken into account when selecting ICE power.