Time Trial Helmets: perfect aerodynamics and protection
Time trial helmets
The closed shell and the extended tail guide the air along the back of the head instead of letting it swirl behind the helmet.
Head position also decides
The shape only works in the position it was designed for. If you lift your head too far, you put the tail crosswise into the wind and lose exactly the advantage for which you bought the helmet. Short tails are more forgiving of this than long ones.
Heat
Without ventilation, heat builds up. For a time trial over a limited distance this is acceptable, but not for long rides in hot weather. Some models have a visor that replaces glasses.
