Thanks Les, I saw that article and its still confusing.
The pic below shows the tire that I'm looking to size. If what it shows, and what I've read previously is true, then the diameter of the there should be 23.5", and the width should be 25.
However looking at the pic its clear to see that the width is not greater than the height. Thus my confusion.
After thinking about the size, I realize that the 23.5 has to be the height of the sidewall, because these tires are massive, but the article doesn't say that.