The side wall height ratio was the same for all the tires with the same wheel diameter while the simple number system was in use. I think it's like 75% (don't quote me on this), so an example would be a 7.00x20 would have a 5.25" sidewall and a 7.50x20 would have a 5.63" sidewall making the 7.50 tire taller by 3/4".
This then gets confusing when you get into mixing tube type with tubeless type tires. The ratios are not the same. Example, a 9.00x20 is the same diameter as a 10.00x22.5 and a 10.00x20 is the same as a 11.00x22.5. So the 22.5 must have a smaller "ratio" number than the 20's have.
Happy New Year!
Mike
