I have a Z1R half helmet in an XL. The large seemed a bit tight to me so I went a size larger and when its all strapped down it feels comfortable without being overly tight. My head measures at one inch above the eye and around the head to the largest point just about 22 1/8 inches. My helmet came with a zipout ear and neck segment that is great on cold days in concert with a burglars mask it does yeoman service keeping the ole skull warm. Not to pricey either. Got mine at the Triumph dealer.
Its hard to determine a true size with a lot of these skull buckets ...seems to be no standard. I need a medium in a Bell half helmet that fits just near perfection/ snug but not to loose whereas the Z1R needs a large or extra large.
