This paper is related to SAC(Steering Automatic Centering) system. In generally, MDPS system is operated by the Driver. In case of driving the vehicle by driver, the Steering power consists of the driver power and the assistant power. In this system, if the Driver would like to array steering wheel to center- direction, the driver does not rotate steering wheel, Because of operating steering- motion automatically. Also, SAC system has the function for centering steering wheel. The detail description is following that. the SAC system is not contacted by the driver power to work steering wheel motion, only MDPS system have an effects on automatic steering motion. If it is completed to control steering wheel to the center area. The Self- Aligned torque is affected by Vehicle tire friction. So vehicle does not last to longitude direction , the steering wheel does not keep center position. So, This problem will be solved by this paper, we are suppose to the control-method s for SAC.