20 inch wheel in a 19 inch frame

I have a 20 x 2.35 unicycle and the frame is cracked. i found a frame that i like but am not sure if it will fit my wheel/tire. it is a quax 19 inch frame https://qu-ax.de/catalog/387-mm-19-Muni-Unicycle-frame-steel-black_1

It should, I think, though don’t take my word for it. The tire will fit (sideways, at least), as yours is 2.35 and the frame takes up to 2.5. The frame itself also apparently fits a 20" wheel (it says at the bottom, “Wheel diameter” and then 19" and 20", and if you search for 20" frames the one you’re looking at comes up). My only thing would be whether the frame can fit a 2.35 tire on a 20" wheel.

You’d also have to check whether the hub fits with the frame, and stuff like that, but that’s another kettle of fish.

It can probably be welded.

What exactly is the difference between the two anyway? It would seem to me that with all the bmx equipment out there that a 20" wheel and tire would be available in just about any configuration necessary, so why the 19"? What is it that it does better than a 20"?

19" size is associated with Trials, where you want a wider tire for flotation and jumping. Tire diameters are slippery things; they are rough estimates based on rim size and tire width. A wider tire will tend to have a larger diameter for a given rim size. So if your tire isn’t too wide, it will also not be too tall. For best results, see if someone can find you an actual fork height to be sure. Measuring from the axle center to bottom of fork crown, or similar, so you can compare that to your existing tire.

I’d be surprised if it didn’t fit, but there is a chance the 2.35 will be a smidgen too tall. I’ve shimmed bearing holders for a few extra mm before.

really for that price I would be willing to give it a try without the guarantee that it would work. Guaranteed it will work with a 2.1" tire or less though.