Transmission gear ratio estimate

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by: Cobalt327, Crosley
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[edit] 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.