Here is a best rule of thumb guide:
For every 10mm change in section width, tire diameter changes by 1/2"
For every 5 percent change in profile percentage, the diameter changes by 1"
The stock early Explorers had 235/75/15's. That means a 235mm section width, and 75 series of tire. The series is the percentage of the section width, which results in the distance from the wheel to the tread.
A 255/70/16 is a later stock common tire, and is 30" tall.
These work with the common tire sizes. I haven't done extensive research to say that 24" rims work this way, or 20 series tires, etc.
The Tire Rack is a good website to use to experiment with tire sizes. Good luck,