Here's what I found covering the two sizing issues. The first is from the 1927 National Wheel and Rim Association catalog, and the second is from a 1945 vendor catalog. The changes made in 1927 are in no way related to the changes made in 1945. It was just that the industry standards changed in major ways these two times. I'm not aware of any other major changes like these until the whole mess that came about in the 60s/70s with metric sizing, "R" coding of wheels approved for radials, and letter/numerical coding of profiles such as G78, etc. Here's the charts that I found. First the 1927, then the 1945. Stu

http://i286.photobucket.com/albums/ll89/truckdog62563/Wheel%20Profiles/rimtireconvertionchart.jpg
http://i286.photobucket.com/albums/ll89/truckdog62563/Wheel%20Profiles/rimtirewidthchart2.jpg