Transmission gear ratio estimate
 Estimating transmission ratios
A way you can get a ballpark figure for what the transmission ratio is - if the car is drivable, and has an accurate tachometer and speedometer:
- Drive the car at 1000 RPM (you can use a different RPM and convert it easily) in whatever transmission gear is 1:1.
- Note the speedometer reading.
- Then put it in whatever transmission gear that you want to know the ratio of, and drive at the exact same speed.
- Note the tach reading.
- you move the decimal point three places to the left, that's your transmission ratio.
Example: If the tach says 3200 RPM, your transmission ratio is 3.2:1.
Also see Gear ratio check for estimating rear gear ratios.