Enter your stock tire dimensions (width, aspect ratio, rim diameter), new tire dimensions, current axle gear ratio, and target highway RPM to find your recommended new gear ratio — plus see how your stock vs. new tire diameters compare and exactly how much your RPM at 65 MPH will shift with the swap.
Recommended New Gear Ratio
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Current Effective Gear Ratio
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Stock Tire Diameter
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New Tire Diameter
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RPM Change at 65 MPH
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Speedometer Error
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Regearing involves changing your axle's ring and pinion gears to adjust the gear ratio. Larger tires effectively raise your gear ratio, reducing acceleration and potentially causing your engine to struggle. Regearing restores proper power delivery and fuel economy.
Check your vehicle's door jamb sticker, owner's manual, or differential tag. You can also divide the number of ring gear teeth by pinion gear teeth, or perform a wheel rotation test by counting driveshaft turns per wheel revolution.
Effective gear ratio shows how your current gears perform with new tires. Recommended gear ratio is the new axle ratio you should install to restore stock performance and maintain optimal engine RPM at highway speeds.
Professional regearing typically costs $1,200-2,500 per axle depending on gear set and labor. It's worth it for significant tire size increases (3+ inches) as it restores drivability, fuel economy, and reduces transmission strain.
For 4WD vehicles, both axles should have the same gear ratio to prevent drivetrain binding and transfer case damage. For 2WD vehicles, you only need to regear the driving axle (rear for RWD, front for FWD).
Without regearing, you'll experience reduced acceleration, lower fuel economy, increased transmission strain, higher engine temperatures, and potential long-term drivetrain damage. Your speedometer will also read incorrectly.
This calculator provides accurate mathematical results based on tire dimensions and gear ratios. However, final gear selection should consider your specific vehicle, driving style, transmission type, and intended use (daily driving vs off-roading).
Common ratios include 3.21, 3.42, 3.55, 3.73, 3.91, 4.10, 4.30, 4.56, 4.88, 5.13, 5.29, and 5.38. Availability depends on your specific axle type. Consult with a gear specialist to confirm what ratios fit your differential.