I used to get flats every week on the crappy trails I rode, so I got thick tires with kevlar in them, and since then I've never had a flat. Nowadays I ride a paved trail though, so I don't think I even need them anymore, and the other day at the bike shop I was putting together these basic commuter bikes with thin tires and I realized they were lighter than my bike. So what do you guys think about this subject? Do lightweight road tires make much of a difference to the average joe on a bike? I've had trouble keeping up with this guy on a mountain bike before, although he was much stronger than me, but it still makes me question whether or not tires affect speed much. The reason I'm asking this is because I LOST my road tires because I'm an idiot, so I can't just swap the tires out to see what the difference is.