X-Fourteen / X-Spirit III, developed putting much value on the use at circuits, sets the position where a rider strongly leans forward as basic position. The shell is designed by analyzing the riding wind running from front part of a helmet to rear, and then to back of racing suit at the wind tunnel facility. The edges and shapes on surface of a shell, rear stabilizer equipping rear flaps exchangeable depending upon riding condition and lower air spoiler are designed and equipped to maximally increase aerodynamic performance. Comparing values in wind tunnel experiment with its predecessor, LIFT, DRAG and YAWING decreased by 3%, 10% and 50% respectively (value for reference measured by in-house facility).