Excellent point, Elkoskoolie! And the answers are all right there in the chart that Phil posted the link to. In the league where I'm trying to play -- 11R and 12R, some tires call for 8.25 inch wide rims, and some call for 9 inch.
But I have a hunch I might get away with a bit of mix-n-mis-match. Here is a tire -- G287 MSA (whatever that it) -- where 12R22.5 calls for 9, while 12R24.5 calls for only 8.25.
Edit: The G287 is an All Position tire -- OK for steering, just a bit bit coarser than a pure steering tire. 44.9 " tall in 12R24.5!
Equally tall money, though, I bet.