High quality vehicle dynamic performances considering human sensitivity, such as ‘feel easy to trace a line’, are required recently and this performance should be designed in closed-loop driving situation. However existing studies about the performance aren’t enough, and real vehicle engineering is still mainly relying on open-loop index design. In this study, a new hypothesis for the vehicle dynamics characteristics which could realize the performance will be proposed, using the driver’s steering operation mechanism analysis in closed-loop situation. Results of verification with a driving simulator and a real vehicle will be also introduced to prove the effect.