I agree that the front wheel pictured is a 22.5" wheel.
Also that the rear wheel pictured is an RH5 20"
The "old tire sizes" are still in use today. for example 8.25x20 and 9R22.5
22.5 or 20 is the rim diameter at the bead seat.
The R indicates radial, and X or - is usually bias ply or could be unspecified depending on where/how it is used.
8.25 or 9 is the nominal tire width at the road, not always same as what you might measure... use more for comparison between sizes. For actual width look up the exact tire specs for that model tire from the tire manufacturer.
The rims they fit on will be somewhat narrower than the tire size. For example a 9R22.5 tire should fit on a 6", 6.75" or 7.5" wide rim (measured at the bead seat).
More info here, page 47 and 48 among others:
http://www.accuridecorp.com/files/2012/10/Accuride-Wheels-Product-Catalog-Summer-2011.pdf
