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Abstract. Development of steering system has begun with manual steering, hydraulic power steering, and electric power steering. The current tendency of the steering system market is that electric power steering systems are increasingly in demand by consumers, which is inversely proportional to the other two, namely manual steering and hydraulic power steering which decrease sales. This is due to, among other things, mild operation and ease in the control system. Although for large vehicles each tends to use hydraulic power steering. University Indonesia has succeeded in developing a large type of electric car, the EV-Bus Molina UI. This bus uses a 200 kW main drive motor, for AC 15 kW, for a 4 kW compressor and 7.5 kW Power Steering. The Power Steering system used is Hydraulic Power Steering. Energy efficiency has reached a range of 60-80%. From the survey data about the use of electric power steering in large cars, neither ICE-BUS and EV-Bus systems have used electric power steering. Because of the superiority of Electric Power Steering, it will be converted from Hydraulic Power Steering to Electric Power Steering on the EV-Bus Molina UI. In this paper, we will explain about the existing dynamic motion equation models in electric power steering. Electric power steering uses a motor booster as a driver assist in driving the steering rod. The booster motor position on the electric power steering is in the steering column or on the steering rack. The booster position of the motor will affect the shape of the overall dynamic motion of the electric power steering system. In the beginning, the equation of the dynamic motion of the electric power steering system only involved a system of stiffness and inertia of the wheel drive, column steering, and tire, but further developments also involved viscous damping and friction of each of these components. The components involved in this movement are also increasing, namely rack and pinion, tie rod and drag link. This is due to the more accurate calculation of the torque needed by the motor booster and its control system. In large cars, the difference between city cars is the distance from the steering rod which is almost 2-3 times that of the city car, so the similarity of the motion will also be different. Stiffness equation is needed for the drag link mechanism structure which involves more stems combined between truss and frame. This is what distinguishes it later with the equation of the dynamic motion of the electric power steering system with the city car and its kind.