Rear suspension system for bicycle

The invention relates to a rear suspension system for a bicycle. When the rotation center of the center track of the back wheel is on the normal riding position (the Sag is 1/4-1/3 of the coherer protector run length), it falls around the point of tangency of a chain and a front teeth plate so as to reduce the trample energy loss. The rotation center of the center track of the back wheel will swing upwards far away from the ground, and it will extend backwards; therefore, it can reduce the pedal back caused by shock absorption. The line passing through the instantaneous center of the rear triangular frame relative to the front triangular frame and through the ground-contacting point of the rear wheel forms an angle of about 45 degrees with the horizon, thus the affection of brake to shock absorption can be decreased to the lowest.