Giro Phase Cycling Helmet Acu Dial suspension offers an easy-to-adjust and supremely stable fit right out of the box Detachable visor provides added protection from sun, rain and the occasional branch In-mold construction and internal reinforcement make this helmet tough Highly tuned, 27-vent design provides superior cooling Sizes: S(20"-21.75"/51-55cm) M/(21.75"-23.25"/55-59cm) L(23.25"-24.75"/59-63cm)