Newbie-style questions re helmet size

Newbie-style questions re helmet size

I’m looking at buying a HJC I70 to replace my Bell Qualifier, size medium, which after a couple of month is still a bit too tight for me and my 58cm head.


Several reviews mention that the helmet is available across the usual range, S to XL etc, in two shell sizes. I’ve no idea what that means — I’m and oldie, not a newbie — and there is no explanation anywhere. Can anyone dispel my ignorance?


I’m also wondering if anyone out there knows from experience if HJC fit tighter or looser than Bell.


Source: Newbie-style questions re helmet size