just a heads up, when i bought my Pyrotech my head measured 22.25" (56.5cm) which is clearly near the low end of medium. however, when i got my helmet it fit nice and snug (which its supposed to) until your head swells up during 100 degree racing comditions. then it gets pretty tight and could cause headaches, etc. so just keep that it mind. you may want to think big.