Also note that the chart provided in the article calculates tire revolutions per mile based on an assumption about tire sizes that is probably not correct. A 33x12.50R15 is probably NOT 33" in diameter.

For a reference, I looked up a 33x12.50 Bridgestone Dueler A/T on their website. They spec at 32.6" diameter, and 639 revs per mile (source: www.bridgestone-usa.com). I expect most brands will give you similar results, but go to your tire mfg's website and look for a spec sheet to be sure.

Using this info to calculate, I come up with a 23-tooth speedo gear (Mitsu part number MD705463) needed for 33x12.50 tires, as opposed to the 22-tooth gear recommended in the article.