I'm also looking at getting new tires for my 05 America. I went to the dealer Friday and looked at the new models. They've kept the same rear size but have gone to a 110/90 18 for the front. Mine also originally came with 110/80 18 and I figure the larger one would fit on mine as well. Basically same size tire just a hair taller. It might also make my speedo more accurate.
I'm not sure why Triumph changed sizes even though they stayed with the same model (880/Lasertec) tires. I'd also love to hear comments on pros and cons of going to the larger tire.