Joined: Dec 2004
Posts: 12,548
Likes: 797
From: Middle of da Mitten
Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, Catrike Speed
You could probably go as narrow as a 26x1.25 Specialized FatBoy, Primo Racer or Kenda Kwest. I think you'll find that if you use a fatter, 1.5-2.0 inch wide slick, it'll still be nearly as slow as a knobby.