I have a 42:17 right now. I find it very comfortable for city riding and I also ride a local "mountain" (it's only 1 mile of climbing at a very steep gradiant) with it. So, I enjoy how snappy it is and I really enjoy climbing on my fixy, but on flats, I spin waaay to fast. All that said, I'm probably going to move down to a 15 toothed cog.