According to Harley, a 180 is as big as you can go for recent years on most Dyna models. I have a 180 on my 2009 FXDC and I agree with Harley. A bigger one would not work. Any bigger and you'd need a different swing arm and a wider fender and probably have to run the wiring outside the fender somehow. BTW, the 180 looks pretty good to me and no mods to the bike.