SMOOTH, COMFORTABLE, AND EFFICIENT: 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.RIDER-FIRST ENGINEERED: Like all Specialized performance bikes, the geometry of each frame 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 ride.