I'm having a surprising amount of difficulty finding a rim that seems like it would work well with a tire in the 50-622 to 60-622 range - something like a Big Apple in 2.0, 2.1 or 2.3, or maybe something with just a small amount more thread.

I'm actually looking at this for a unicycle for 50+ mile rail-trail rides (where I'm currently using a giant 36-2.75") and occasional relaxed bike events, and had always thought that 29" was an everyday bike size that would make things simple. Maybe I've been mislead by the Citibikes all over Manhattan, but it seems this isn't so common at all.

Unicycle suppliers sell 42 and 52mm OD 622 rims, but these seem to be too wide for anything but extreme offroad tires - in fact there seems to have been a trend of mountain bikers buying them for that. It'd assumed I'd just get the 42mm rim which is probably around 36mm ID, but after more research it seems like it is not what I want: allegedly they have problems retaining 50-60mm tires, and even when they do, they spread them too far, causing a too-square profile which handles poorly and makes things like road camber a constant battle. I really don't want to go to a tire smaller than 45mm, and would prefer something over 50mm.

I think that means I'd be looking for a rim in the 22-30 mm inner diameter range, but am not seeing a lot there (I'm also constrained to 36 holes by the unique 1.5x geared hub I'd build this around, and will probably continue to use a rim brake for hills)

People have used the Velocity Dyad on unicycles, but it's theoretically too narrow at only 18.6mm ID.

Another mentioned long ago was the Rhyno Lite - these seem a bit rare, but have some possibility at 22 mm.

In my own searching I found the Cliffhanger at 25mm - but a very flat profile that is a apparently very hard to mount tires on since there's no well to park the opposite bead in.

And then there's the question of the tire itself - had started out assuming I wanted a big apple, now less certain. I'm mostly riding paved rail trails, but access to one is gated by a mile of dirt (sometimes mud) to the NYC/Westchester line, and some others further afield have stone dust. The huge 36" wheel I'm on now deals with most of that, but the idea here is to get something more compact and easier to manage when traveling, and (at least in the lower direct drive gear) easier to get onto and off of in stop-and-go event situations.

Any ideas?