Enter your Tire Diameter, Vehicle Speed, Engine RPM, and Transmission Gear Ratio to calculate your Rear Axle Ratio — plus see your Theoretical Speed at Given RPM and RPM at Given Speed so you know exactly how your drivetrain is performing at any gear.
Rear Axle Ratio
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Theoretical Speed at Given RPM
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RPM at Given Speed
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The axle ratio is the gear reduction in your rear differential, expressed as a ratio like 3.73:1. It determines how many times the driveshaft turns for each wheel rotation, affecting acceleration, fuel economy, and towing capacity.
Check your vehicle's door jamb sticker, owner's manual, or differential cover tag. You can also calculate it by marking your tire and driveshaft, then counting rotations when turning the wheel by hand.
Lower numerical ratios (like 2.73:1) provide better fuel economy and higher top speeds but less acceleration. Higher ratios (like 4.10:1) give better acceleration and towing power but lower fuel economy.
Larger tires effectively lower your gear ratio, reducing acceleration but increasing top speed. Smaller tires have the opposite effect, acting like a higher gear ratio with better acceleration but lower top speed.
Yes, transmission gear ratios multiply with axle ratios to determine final drive ratio. Use 1.0 for direct drive (usually 4th gear), or the actual overdrive ratio for highway calculations.
Higher numerical ratios like 3.73:1 to 4.30:1 are typically better for towing as they provide more torque multiplication and better pulling power, especially when starting from a stop or climbing hills.
Yes, you can change ring and pinion gears in your differential, but it requires professional installation and may affect other components. Consider the impact on speedometer accuracy, warranty, and overall vehicle performance.
This calculator provides theoretical results based on input values. Real-world results may vary due to tire pressure, wear, transmission efficiency, and other factors. Use it for planning and estimation purposes.