Bmx helmet full face bike helmet mountain bike helmet suitable for men sizes 51 55 cm 55 59 cm 59 63 cm main colour black number of air vents 10 visor with visor size adjustment pads features chin ventilation chin guard outer material carbon weight 1 050 g helmet technologies bell overbrow ventilation bell velocity flow ventilation marks of approval astm f 1952 astm f 2032 cpsc en din 1078