Regear Calculator (Off-Road)

When you fit larger tires to a 4x4 or truck, your engine has to work harder and your speedometer reads incorrectly — regearing restores the original power and highway cruising feel by changing the axle's ring and pinion ratio. Enter your stock tire size (width, aspect ratio, rim diameter) and new tire size alongside your current axle gear ratio and target highway RPM to get the recommended new gear ratio. Secondary outputs include your current effective gear ratio, calculated tire diameters, RPM change at 65 MPH, and speedometer error percentage.

mm
%
in
mm
%
in

Your current ring and pinion gear ratio (e.g. 3.73, 4.10, 4.56)

RPM

Desired engine RPM at highway speed (65 MPH)

Results

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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Frequently Asked Questions

What is regearing and why do I need it after installing larger tires?

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.

How do I find my current axle gear ratio?

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.

What's the difference between effective gear ratio and recommended gear ratio?

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.

How much will regearing cost and is it worth it?

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.

Can I regear just the rear axle or do I need to do both front and rear?

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).

What happens if I don't regear after installing larger tires?

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.

How accurate is this regear calculator?

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).

What gear ratios are commonly available for my axle?

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.