I'm currently 295 pounds and this summer have been riding a Specialized Crosstrail. It still has 100% stock components and in most respects I love the bike, but it feels sluggish. I can pretty much ride it on roads all day, but only at like 14 mph. I can get it up to 22 but with a level of exertion that I can't keep up for very long. Since I otherwise love the bike and would just like to speed it up a bit (I'd like my "distance" speed to be more like 18) I've been thinking of trying it with smaller, smoother tires.
The tires on the bike right now are 700x38 with a knobbly tread (specialized trigger sport). Rough terrain is no problem at all; they're not great on sand or mud but anything short of that almost isn't even noticeable. I have had no flats. I inflate them to 100psi and seem to lose 5-10 on a typical ride. They really seem pretty bulletproof.
Thing is, even though it's great on rough terrain I am on pavement most of the time. So I was thinking of putting a 32 or 28 city tire on it. The questions are, is this advisable at my weight, and would it make any appreciable difference? Or is the answer just to get in better shape or get a road bike? I've test ridden a few road bikes and I am just not crazy about drop handlebars.