Originally Posted by
usndoc2011
3) size- I have commuted on 23s and 32s, and honestly, I'm not totally convinced there is an astounding amount of a difference (althought there probably is some). I feel more comfortable with bigger tires: the wheels seem more stout, they seem to tackle bumps a little better, I have less heartburn over potholes and curbs because I'm not as worried about a pinch, and they do seem to absorb a little more of the road. That said, the main advantage of larger tires seems to be that they can be run a slightly lower pressures for a softer ride and more traction without risking a pinch flat as much. I prefer to keep my tires maximally inflated (110psi on my 28s) because I want a quick ride and I don't want a pinch flat, so the ride quality is only slightly improved over the 23s I ran when I first started commuting. As far as speed and keeping up with riding buddies, at least for tires at or below 32, I don't think that the tires will be what hold you back. I've been crushed by dudes on knobby tired mountain bikes, and I'm pretty quick.
The key to getting benefits from wider tires is finding the optimal pressure, which varies depending on your weight. Generally, a 700x28 tire at 110 psi is probably even harsher than a 700x23 tire at the same pressure for most riders, and possibly slower in many circumstances than a 700x28 at lower pressure.
This article from Bicycle Quarterly has a very helpful chart to help you figure out the ideal tire pressure.
I'm also a speed freak, and so I'm very reluctant to give up tire pressure on smooth pavement. On the other hand, I've learned from CX racing that on irregular surfaces you get less rolling resistance from lower pressure. When I first got my 700x28 GP 4 Seasons I grudgingly tried them at the 95 psi that I read somewhere as recommended. That worked pretty well for speed, but I was still feeling the bumps from all the fall debris in the road. The article above suggested that 95 psi rear/80 psi front was best for me. Though skeptical, I gave it a try. My experience is that at 80 psi I started feeling very slightly slower, but at 85 it felt at least as fast as 95 and the bumps were softer. I'm experimenting now between 80 and 85 to get it dialed in just right.