Regearing Guide for Jeep Wranglers — Why and When to Regear

Why Regearing Matters

Changing to larger tires without regearing the differentials has several negative effects. The engine operates at lower RPM at highway speeds, which takes it out of its power band. The vehicle feels sluggish off the line and struggles on grades. The transmission hunts for gears constantly. The speedometer and odometer read incorrectly. The fuel economy drops because the engine is working harder than it should.

Regearing replaces the ring and pinion gears in the differentials to restore the effective gear ratio to what it was with the stock tires. The goal is to get the engine RPM back to where it was with stock tires for a given speed. A correctly geared Wrangler drives better, accelerates better, gets better fuel economy, and puts less stress on the transmission.

Choosing the Right Gear Ratio

The correct gear ratio depends on your tire size, engine, transmission, and how you use the vehicle. For a 3.6L Pentastar with automatic transmission and 35-inch tires, 4.56 gears are a good choice. For 35s with the manual transmission, 4.88 gears work better because of the manual's different gear spacing. For 37-inch tires, 5.13 gears are needed regardless of transmission. For 33-inch tires on a JK with the automatic, 4.10 gears are sufficient.

An online gear ratio calculator can help determine the right ratio for your setup. Enter your tire diameter, current gear ratio, and transmission gear ratios to see the engine RPM at highway speed. The target is 2,000 to 2,200 RPM at 70 mph for the Pentastar, or 2,200 to 2,400 RPM for the 3.8L and 4.0L engines. If the calculated RPM is below this range, the gear ratio is too tall.

The Regearing Process

Regearing requires specialized knowledge and tools. The ring and pinion gears must be set up with the correct backlash and pinion depth. If the gear setup is incorrect, the new gears will whine and wear out prematurely. Most owners have a professional shop do the regearing, which costs $1,200 to $1,800 per axle including parts and labor. Both front and rear axles must be regeared to the same ratio.

When regearing, also consider upgrading the differential covers to aftermarket units with drain plugs and cooling fins. Replace the axle seals and bearings while the axles are open. If you are installing a locker, now is the time to do it since the differential is already disassembled. Plan the total job carefully to avoid paying labor twice.

Bottom Line

Regearing is essential when running tires larger than 33 inches on a Wrangler. It restores acceleration, improves fuel economy, and reduces strain on the transmission. Use an online calculator to determine the correct ratio for your specific setup. Have the work done by a professional shop with experience setting up ring and pinion gears.

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