I have a new 60 cm Americano Co-Pilot that came equipped with Vittoria Randonneurr Pro 700x35 tires mounted on Velocity Dyad rims. Since I am new to loaded touring, I have no real frame of reference to judge these tires and to know whether they are overkill for what my needs are or not. I've taken a couple of short local tours and had zero tire issues so far.
So, I would like some help in assessing whether I really need a 35mm tire. I'm 230ish, bike weighs 31# and my load, including panniers and water bottles is about 40#, about 300# all in. My first "real tour" will probably be a month or so around the southeast US (Georgia/Florida Gulf Coast & Panhandle) and the anticipated riding surfaces include very limited gravel and the best two lane roads I can find...so nothing extreme at all. Load is distributed between front and rear Ortlieb panniers, I'd guess 35% front, 65% rear.
First, what options do I have regarding tire size?
Second, how much easier would a narrower tire (let's say a 28mm) would be to pedal (i.e., is there a meaningful lowering of rolling resistance??).
Third, given my specific configuration and planned riding surfaces, do I need the added durability that I presume I'd get with a wider tire?
And last, are there reasons other than those above that I should consider leaving well enough alone?