This bike sounds a lot like the Rosco Roads, which used SimpleOne forks, but tire clearance with fenders is apparently better . My Rosco Road has 130mm rear spacing and I do 700x35 to be on
the safe side, but could probably do 700x38. The RU is supposed to do
700x45 with fenders. I wouldn't have guessed that'd be easy to do with
120mm frame spacing, but the Quickbeam probably gets pretty close to that, right? I assume the frame is spaced at 120, and not just the hub.
120mm frame spacing is desirable because it allows a larger chainring (>40t) to be installed with good chainline on a 120mm hub which aren't really specialty items. I've done several conversions of 120mm wheels on 126mm and 130mm frames using axle spacers to make up the difference. A 120 fixed or free rear hub dictates chainring choice. You basically have to run what will not hit the chainstay while giving good chainline. Often that means something smaller than 42t. A 42x15 is a nice combination for just riding around, but if you want a bigger gear, you're out of luck. Better to go with a bigger front ring like a 44 or a 46 and then you can swap out freewheels and cogs to get the combo you want. If you don't care about riding fixed, 130mm hub spacing is easy, because you can just use a regular road cassette hub and adjust the chainline on the rear wheel using spacer kits like the kind Surly makes. Then you can put a bigger chainring on the outside of the spider or use a longer BB to get the ring clear of the chainstay.