I went from an automatic to a toploader, I also went to 16" tires, can’t remember the exact size but after reading the recipe for the teeth to tire to mile ratio, thought I would just see what others think before buying 5 or 6 different speedo gears… Does not have to be perfect cause I never do the speed limit anyways, just want to be close, right now it does not work at all with the auto gear…
For whatever reason, my speedo is off, it shows 20% less than the real value.
In the process of figuring out how to rectify it (low on my priority list at the moment), a good guy gave me lots of info including this link. Hope it helps!