A brake system for bicycles includes two pivotably connected first and second arms and two brake pads are respectively connected to the first and second arms. A cable unit is connected to the second arm and includes a brake cable. A link unit includes a first link which is connected between the second arm and the brake cable. A second link has a first end connected to the first arm and a second end of the second link is pivotably connected to a mediate portion of the first link. The distance between the two ends of the first link is longer than the distance between the second end of the first link to the second end of the second link. The brake cable is lifted with less force, the first link lifts the second link which moves the first arm to pivot to stop the wheel rim.