When I ran pneumatics in an urban commute I found that my road bike flatted frequently while the mtb w/knobbies, rarely. My commute was 20 mi rt all on high traffic roads w/plenty of debris. I think I flatted on my mtb once in four years. The tires were a set I found in a dumpster attached to an X-Mart mtb. Had Mr Tuffys in both the roadie and the mtb. Kenda Kwest 700x28mm on the roadie. Seemed every other time I'd ride my rb I'd get a flat, so I just rode the mtb for a couple of years, unless I had a mechanical of some sort. My commute's 40 mi rt now and I use airless on all 3 of my commuters...no stress.