To me, it's the wrong question. The right question, to me, is "what is the minimum width tire that makes you confident you can roll over anything in your path that you could possibly not see"? Because you're just not going to see *everything* riding at night unless you have a lighting system that costs about $1000 or go stupendously slow.

To me, the answer is about 1.5" (37mm) tires on a paved road at 20mph with a reasonable light (200L Dinotte). To knock that down to 23mm tires, we're talking about a much brighter light and much lower speed.

So in winter, counterintuitively, I go much faster on wider tires than thinner. I roll over all kind of bumps, potholes, tree debris, rocks, etc that I may not see on the nice wide things.