Greg, this may help with how a tire is sized:
The actual tread width should be close to the wheel width. The section width should be a little wider than the wheel width. I've seen original Cobra 427's using Sunburst wheels with tires far too wide on the rear for the wheels. The tread edges actually curves down and the center of the tread sticks up. The owners are trying to fill up the rear fenders with big tires but the wheels weren't designed for the tires that wide. They just need to understand that there was a lot of excess space on wide fendered cars and leave it as originally intended. It's a pet-peeve of mine!
Note the rear tires that are far too wide for the wheels:
Larry