Gearing Calculator

This is a gear ratio calculator designed to help our customers decide on the best transmission and differential choice for their purposes. If you're curious how changing ratios will affect your gearing, this tool will remove the guesswork.

This calculator includes the three BMW transmissions used in our transmission upgrade kits for both K series and Mazda BP powered Miatas. 

GM Getrag diff ratios are also included with the Miata diff ratios. These can be installed with a Getrag diff upgrade kit from V8 Roadsters, and it's a recommended upgrade for high horsepower cars.


Tire Width (mm):
Tire Aspect Ratio:
Wheel Size (inches):
Engine Redline RPM:
Ratio Preset:
1st Gear:
2nd Gear:
3rd Gear:
4th Gear:
5th Gear:
6th Gear:
Cruising Speed (MPH):
Cruising RPM: