I've run across a number of great sites with very useful calculators using variables for wheel diameter, final drive ratio, tranny gearing, etc., etc., and then they'll solve for some other variable like RPM, speed or crawl. And I really love them, I do.

What is a bit more elusive is a site where all the formulas behind the calculators are listed. That's what I'd like to find, because I'd like to build my own spreadsheet to compare a couple of tranny / differential scenarios side-by-side.

Sites like this:

Automotive Converters and Calculators

have a boatload of different calculators, but if you know any links to the formulas behind these calculations, it'd appreciate it greatly.