GypsyWolf_Rider said:
so ill see what i can do with a 24"x2.5" bike tire and try and keep from ruining the rim and the tube.
If you have an actual *20"* (507mm) rim, then that's a 24" wheel (not 20"), just so you know what you are looking for.
https://en.wikipedia.org/wiki/Bicycle_wheel#24_inch_/_ISO_507_mm
For those, I haven't tried anything other than bicycle tires, but as noted by someone else above, some people have fit certain vintage tire types on them.
But a 24" tire cannot fit on a 20" wheel (16" rim), it is far too large inside diameter. Usually the entire 20" wheel *and tire* will fit inside the 24" tire's bead.
GypsyWolf_Rider said:
If it's a 20 inch bicycle wheel, then the rim itself is 16", and will fit many 16" moped / scooter / etc tires as long as it is wide enough to fit teh whole bead (which is much thicker than bicycle tires) between the rim and the valve stem.
But there are two different sizes for 20" rims, 406 and 451mm. It's a big enough difference in size that the moped tire will fit one but not the other. (if it fits the bigger one it may blow off the smaller one). But the bigger ones are usually very narrow and unlikely to fit the moped tire anyway.
https://en.wikipedia.org/wiki/Bicycle_wheel#BMX_wheels
I'm using Shinko SR714 16" x 2.5" tires on my SB Cruiser's "20"" rear wheels, and it gives me something over 22" actual diameter.
As soon as I get the fender frames / etc around the wheel area rebuilt for more space, those will be changed to the 80/90 version of the same tire, which could make them almost 26" actual diameter, from what I've read around various places (but at least 24"), which will help with easier rolling over problematic road surfaces, and add more air volume for that too.
. I fired off an email to east gem http://www.eastgem.net/tire-24x3.html 
