Gear Ratio Calculator
Calculate gear ratio, final drive ratio, and vehicle speed from tire size, transmission gear, and RPM.
How It Works
Enter engine RPM, tire diameter, transmission gear ratio, and final drive ratio. The calculator determines vehicle speed and effective overall gear ratio.
Formula
Speed (mph) = (RPM x Tire Diameter) / (Gear Ratio x Final Drive x 336)
Frequently Asked Questions
What is final drive ratio?
The final drive ratio (rear end or differential ratio) is the last gear reduction before the wheels. A higher ratio (e.g. 4.10) accelerates better; a lower ratio (e.g. 2.73) improves fuel economy and top speed.
How does tire size affect gear ratio?
Larger tires effectively lower your gear ratio (like installing taller gears). Smaller tires raise the effective ratio. Changing tire size affects speedometer accuracy and acceleration.