I had a commuter bike with 26" wheels. Usual commute tire was a 1.5" slick. For the fun of it, I ran 2.5" Maxxis Hookworms, which weigh more per tire than some lightweight wheelsets. Super fun ride, but slower and I could definitely feel the weight. Better option was 2.35" Schwalbe Big Apples. Again, a better, fun ride, but without as much of the weight penalty as the hookworms. I still commute on bombproof 1.5" tires, but I wouldn't talk anyone out of wider tires.