RPM Calculator
Gear Ratio for New Tire Size
Transmission Final Gear Ratio
Transmission Reference Guide
- Auto refers to direct drive in AOD (1:1 ratio)
- AOD calculations use .70 overdrive ratio
- 5-speed manual uses .80 overdrive ratio
- Modern vehicles often have deeper overdrive ratios – for example, Toyota Tacoma/Tundra 6-speed autos use .58:1
- For custom ratios: multiply 1:1 RPM by your transmission’s overdrive ratio
Optimal Engine RPM @ Highway Speed (60mph)
This reference chart shows ideal RPM ranges at 60mph for various engine types.
Pro tip: When using the calculator, input your gear ratio, tire height, and 60mph to check if your setup falls within these recommended ranges.
Example: A Jeep with inline-6 engine and standard transmission should operate between 2000-3000 RPM at highway speeds. With 35″ tires and 4.88 gears, you’ll achieve this sweet spot for power and efficiency.
| 4 cylinder engines | 2200-3200 |
| 6 cylinder engines | 2000-3000 |
| V8 small block | 1800-2800 |
| V8 big block | 1600-2600 |
| GM Duramax diesel | 1800-2800 |
| Ford Powerstroke (naturally aspirated) | 1600-2500 |
| Ford Powerstroke (turbocharged) | 1400-2200 |
| Dodge/RAM Cummins diesel | 1400-2200 |
About These Calculators
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Our calculators provide approximate engine RPM based on three key factors: differential gear ratio, tire height (measured from ground to top of mounted tire), and transmission gear ratio.
DISCLAIMER: These calculations are estimates only. They don’t account for drivetrain losses, terrain variations, weather conditions, or driving style. Higher engine RPMs typically allow greater speed potential but at the expense of fuel economy, heat generation, and engine longevity. Actual results may vary significantly from these theoretical calculations.
