Gear Ratio Calculator
Match tire diameter, axle ratio, and highway speed. Convert MPH to RPM, plan regearing, then cross-check the master chart below.
Gear Ratio Calculator
Estimate engine RPM at cruising speed or see what road speed corresponds to a target RPM using the standard 336 constant and tire diameter in inches.
Speed ➜ RPM
Estimated RPM
2713
Based on 4.10 final drive & 33" tire.
RPM ➜ Speed
Estimated Speed
59.9 mph
At 2,500 RPM with 4.10 gears.
Balanced gearing for mixed city/highway driving.
Simple formula
RPM = (MPH × Gear Ratio × 336) ÷ Tire Diameter. Works for any axle ratio and rolling diameter.
When to regear
If RPM drops below your engine’s power band after upsizing tires, consider numerically higher gears (4.56, 4.88, etc.).
Match front & rear
4WD and AWD rigs require the same axle ratio on both ends. Always regear both axles together.
How to use the chart
The chart below mirrors the provided Gear Ratio Chart reference. Pick your tire diameter row, then read across to see the calculated RPM at 65 mph for axle ratios between 2.73 and 6.17. Cells progress from cool blues (lower RPM) to warm yellows (higher RPM).
Compare with calculator
After spotting a promising ratio in the chart, plug the same tire diameter and axle ratio into the calculator to model different highway speeds or to see how a target RPM translates to MPH.
Gear ratio planning tips
- Off-road rigs: Larger tires and added weight often like 4.56+ gears to regain factory RPM at cruise.
- Tow vehicles: Keep RPM in the torque band when towing; numerically higher gears prevent constant hunting.
- EV swaps: Use the chart to match reduction gearboxes to tire size so regen and top speed stay usable.
- Legal limits: Some regions require speedometers to read high by up to 10%. Pair this with the Speedometer Calibration tool if you change tire size.
Helpful tools & charts
- Use the tire size calculator to confirm diameter before you plug values into the gear chart.
- After regearing, verify indicated speed vs actual with the speedometer calibration calculator.
- Need more diameter ideas? Browse the 17" tire size chart for common combos.
Gear ratio FAQ
How do I pick the right gear ratio after changing tires?+
Calculate highway RPM with your new tire diameter using this calculator, then compare to your stock RPM. Ratios that keep RPM within ±3% of stock usually preserve drivability.
What tools should I pair with this calculator?+
Run the tire size calculator for exact diameters, then use the speedometer calibration page to verify dash accuracy before finalizing a ratio.
Can I model EV or hybrid swaps?+
Yes. Enter the fixed reduction ratio as “axle ratio” and your target tire diameter to plot RPM vs mph, then adjust for your motor’s best efficiency band.
What about staggered setups?+
Use the calculator twice—once per axle—to confirm front and rear RPM at the same vehicle speed. Match the transfer case ratio accordingly.
How should towing affect my choice?+
Choose a numerically higher ratio so highway RPM sits in the engine’s torque band. Cross check with the speedometer calibration tool to keep the dash honest.
Disclaimer
The calculations and recommendations on this site are for informational purposes only. Always consult your vehicle manufacturer, tire professional, and local regulations before making any changes to tire or wheel size.