Morning, I need to order some tires and i'm having difficulty figuring out my rear rim size? I searched the archives and assumed I had 4.00H18-4PR - 110/90-18. but on further digging I noticed that some people mentioned a 16 inch - 130/90-16? My bike is a 77-78 I read in a post that In 78 they made three models. The standard, the Special and the Special II. The standard had an 18 inch rear, the Special had the mag 16 inch, the Special II had an 18 inch front and 16 rear alloy. When I measure my rim (lip to lip) it measures 17inchs? Any idea if it's a 16in or an 18inch? Thanks! I'm trying not to ask stupid questions but I wanna order the correct size tires!