In my experience my medium C3 fits and I consider myself a typical medium intermediate oval head. I wear a medium in Arai, Shoei and Shark. I would say that the C3 sizing is in line with premium competitors sizing if you have a intermediate oval or intermediate round oval head shape.
If you have an extreme round or extreme long oval head you may have to go up in size, and even then there is no guarantee's. If you are an extreme in either direction this is probably not the ideal helmet to buy without trying it on.
Feel free to ping me on anything else.
Originally Posted by rjdills
I have a C2 I sourced from Germany a few years back. If I remember correctly, it recommended to purchase one size larger than I use in other brands . Large verses medium. Any such advice floating around n theC3?