700x23
When I originally bought my Trek 2120 it came with Trek ISO 3K 700x25 tires on it. That was more surface contact than I wanted or needed for the type of riding that I do. It's pretty basic physics that a larger contact area means more rolling resistance. Thus when I wore out those original tires I opted to switch to the much narrower profile Vittoria TechoTwin Tread 700x20 tires. This was a huge improvement, but in hindsight probably less of a function of their width, but rather their lower weight. If you don't cycle you likely don't understand what a huge difference lightweight tires make.
I've ridden on 700x20 tires ever since. But after numerous pinch flats, a torn sidewall and my increasingly aching old body, I decided it was time to try something different. I had also read that on rough roads —which is the rule rather than the exception in Western New York, wider tires provide more consistent road contact and in turn will increase your speed. Thus the decision was made that when it came time for new tires, I would switch to a 700x23 tire. So a couple of weeks ago I took my first ride on my new 700x23 Vittoria Rubino Pro tires. And I'm now quite happy that I made the switch. I haven't noticed a decrease in my performance and the ride comfort is definately much better. The numerous moderate sized holes I encounter are now glided over and some of the larger bone jarring thuds are now merely annoying bumps. I can now only wonder why I didn't make this switch sooner. :)