will a Michelin commander 180 65 16 fit on my fat bob. the stock tire is a 180 70 16 and was wondering if it would change anything as far as the speedo goes or handling

 

It should fit but the sidewall is going to be a little shorter. So that means the diameter is going to be smaller, so speedo will read a little fast.

 

Even the mich commander II 200mm will fit on a Fatbob... front fits up to 150mm no mods necessary, but I agree with Ohio, the spedo will read faster than you are actually moving. ( not by much but still)