Tech Tip: http://www.stovebolt.com/techtips/wheels/

7.50x20 updates to 8x22.5, but I don't think you can get 8x22.5 tires any more.
9R22.5 is the next choice. However there are some lower profile 22.5 tires, but they are wider than you may want.

for 9R22.5 tires the book calls for 6.75" or 7.5" wide rims. I have some on 5.25" rims, they fit fine but probably should not be loaded to the max.

More details about what tires are equivalent to what newer ones, and what rims width is recommended for what tires can be found in the Accuride catalog, linked in the tech tip, or here: http://www.accuridewheels.com/completeversion.pdf

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-