I just went from 46/17 to 46/19 from like 71.4GI to 64.8 I believe. I'm actually having fun with it, I'm thinking about sticking with it on both of my setups even though 46/19 was just supposed to be for the townie. I agree that a 19t cog looks a little silly, but who really cares. My wheel was about halfway back in the dropouts with the 17, when I put the 19 on there is just enough room left in the drop out that I can get the chain on and off. As long as your weren't too far forward 2 teeth won't be a big deal, but otherwise you might need to add link or a half link like they have already said.