Sirrus X 1.0The Specialized Sirrus X provides the smoothest ride in its class. With bigger, confidence inspiring tires, a slightly more upright riding position, and a super intuitive one by drivetrain. Each frame size is uniquely crafted. This means that for every frame, each tube size is specifically selected to achieve the optimal balance of rigidity, weight, and responsiveness to ensure that no matter what size youre riding, you will experience the worlds best