Originally Posted by Badger6

Each fender is slightly different, in terms of its dimensions. in some cases fenders will further reduce the maximum tire size you can utilize.

Reference my comments about clearances, when you add fenders, clearances get further reduced, in most (all?) cases. Tire clearance on your bike is defined by the width (outer dimension of the sidewalls when inflated to a reasonable pressure, say 3-4 bar), but it also takes into account the diameter of the tire when inflated also (see the clearance at the Bottom Bracket and at the bottom of the fork crown crown, and if one is present the brake bridge at the top of the seat stays. As soon as you mount fenders you lose some amount of clearance at those points in relation to the tread of the tire. My guess is that going to 40s while doable on a bike without fenders mounted, albeit with greatly reduced clearances, is impossible if you plan to mount fenders. I'd have to see the steed to be certain. That's why I suggested staying within the recommended tire size, at least initially. As for when I find fenders unnecessary...in the summer. I have a bike with fenders mounted available continually from 1. November to 31. March. It simply rains too much here, and excepting a few places, there is simply too much sand and muck on the ground, even on the paved (asphalt, cobbles, concrete farm paths, and even the Fietspaden in Flanders). Mount them, and keep them mounted, you won't regret it.

I don't think the Schwalbe G-One R is a good tire for what you described as your normal surface. Allround is probably the best option.