If properly selected, an electric motor (EM) with a fitted power envelope could respond the Electric Vehicle (EV) needs and avoid overdesign. This paper proposes an iterative algorithm upon which, EV designers could define a proper motor and evaluate it by its impact on EV total mass reduction. To simplify the EV design, two characteristics of EM have been recognized to be more essential to enhance, namely, constant power speed range (CPSR) and overall efficiency over the selected driving cycles. A full-battery powered three-wheel roadster prototype and its motor is analyzed, then, another sample motor with higher CPSR is proposed to remove part of the powertrain overdesign. Having limited test data, inverse distance weighted interpolation has been applied to extract the efficiency of electric motor at any operating point. Finally, based on the EV overdesign and its total efficiency, a comparison between the two motors has been made.