There are many more driven gears available than drive gears. In traditional GM transmissions, typically available TH350 (also fits most manual boxes) driven gear selection ranges from 18 to 25 teeth.

Bear with me while I complain like a little girl whose shoes are too tight. I'm sick of answering the same "Why doesn't my speedometer register correctly since I swapped tire sizes?" question over and ...

How many times have you found yourself suddenly confronted by a speed limit sign, then in a panic you look at the bouncing speedometer pointer and immediately start doing math in your head. "Let's see ...