I've always been able to find calculation spreadsheets that would give you a particular size for the tire entered. What I haven't been able to find is a spreadsheet that would give you different widths and aspect ratio for specific diameters and wheel sizes, so I decided to write one. Here it is for the whole community to use.
If you find you want something added to it, let me know and I'll see what I can do.

Edit: Update file with RPM and speed calculations along with converter slip.

 

4wheelparts.com has something like that I think. I know it will tell you what gear ratio you need for each tire, bolt pattern look up, etc....

PS, that zip file won't open on my computer. I get the message that the file is "corrupt" or something.