The Bullet helmet provides an answer to the age-old dilemma of ventilation versus aerodynamics with its narrow shape & closed shell it is a seriously aerodynamic helmet but a quick adjustment to the Airslide system turns it into a helmet with sufficient ventilation to tackle climbs on hot days. With four available sizes the Bullet helmet will provide you with a snug fit & a helmet that is well fitting. This in turn creates a narrow shape with a small frontal area creating the drop like shape of the helmet In combination with the closed shell this creates the aerodynamic performance to make the Bullet into a sprint helmet When ventilation is required the Airslide system can be utilized to open up the front of the helmet & create an airflow throughout with exhaust vents at the rear When ventilation is of lesser importance the entire Airslide system can be exchanged for a fully closed cap creating an even more aerodynamic version of the helmet On top of this performance the Bullet helmet also allows a quick & easy installation of the Life BEAM technology to measure your heart rate or the Inclination Sensor to monitor your head position on the bike Fast like a bullet its the perfect combination of aerodynamics & ventilation whenever you need it!