You know what you want from your helmet. It should protect you, fit you well and be comfortable. It would also be great if it wasn’t hard on the eyes. After years of testing and listening to what professional racers told us about their needs, we managed to create Zappi.The NOW Zappi went through various tests in wind tunnel facility to measure aerodynamic performance and to make sure that the helmet is designed to be fast. Zappi features Effective Stabilized Aerodynamic System Design, Skeleton Inner Construction system for maximum protection, Easy Quick Dial Fitting System and super light weight for best comfort, and 32 vents to keep you cool during your journey.Size: S/M: 20.8 - 22.8 inches (53-58 cm) L/XL: 22.8 - 24.8 inches (58-63 cm)Effective Stabilized Aerodynamic System Design.-Wind Tunnel tested for aerodynamic performance.-Designed and engineered to be super light weight; Easy Quick Dial Fitting System.