As we talk about 20" (tube type) vs. 22.5" (tubeless) rims and tires we need to remember that the 22.5's were designed to be exact diameter replacements for the 20's. So, having a 2-1/2" taller rim doesn't always mean you'll have a taller tire/rim combination.
Here's a list of how the tire sized match up...you can have a 22.5 running right next to a 20 as follows;
7.50x20 = 8.25x22.5
8.25x20 = 9.00x22.5
9.00x20 = 10.00x22.5
10.00x20 = 11.00x22.5
Hope this helps,
Mike B
