ODO MPH - 20 x 21 - Odometer Gear MPH (US)

Odometer Gear MPH (US)
If the gear is crumbled and you can’t count the gears anymore, you need to count the partner gear. So the total number of teeth of the partner gear added with your crumbled gear should always be 70. So if your partner gear has 49 teeth, you need a new gear with 21 teeth.