I love a 52-53X15,16,17 setup. It is like getting a freight train rolling and stopping once you get up to 21-23 mph. I was blowing by folks on the Greenway, and did a couple centuries with that set up. Of course once I started commuting 50+ miles a day, I came back to earth, I'll still hit 20-21 mph, but it isn't quite so hard on the knees, I'm enjoying either a 46 or 48 X 15, 16, 17. I have a couple frames that I switch the wheel sets on depending on my mood, and what I'm looking to accomplish.