Yeah I got it figured out. There is no such thing as a 4 stroke version. The one that the guy behind the counter was referring to was the new 120/90-19 profile. It is a bit wider and better for the desert. The appropriate profile for the rear of the CRF450 is the 110/90-19 which is what they put on my bike. The guy behind the counter was either confused or didnt know what he was talking about. Either way I am going back tomorrow to have a chat with them........and get some money back!