Wider rear tire

I ride an '01 FXSTDI and am considering/wanting to put a wider tire on the rear. Does anyone know why I can't just go from a 160/70 17 series to the 180/70 17 size tire without putting on the wide tire kit that Harley offers? It seem that if the tire is already centered then adding a tire that fits in the fender would not need a special kit. What's wrong with my logic?

It's not the fender clearance that will bite ya, it's the belt clearance. Also a 180/70 would be a very tall tire. If you go to a 180, you would have to drop down in aspect size, i.e 180/55. I'm putting a 180/55/18 tire on my Duece as soon as my wheels arrive.

Does anyone have an insider on installing a 150 on my 01 Wide Glide? Harley dealers only have literature on the softail conversion.

Thanks Sliverbullet for the info. My next question are has anyone actually changed the rear tire on a deuce to a wider tire and if so what size? Did you have to put on a wide tire kit? And lastly did you change to a wider tire on the stock 17 inch rim?

Thanks