The rule of thumb most shops repeat — "regear at 35s" — is close but not universal. The right answer depends on the factory gear ratio, the transmission, and how the vehicle is used.
Why bigger tires need taller gears
A larger tire turns fewer times per mile. With the same axle ratio, the engine spins slower at any given speed — which sounds good until you realize the engine is now below its torque curve at highway speeds. Acceleration suffers, the transmission hunts for gears, and fuel economy drops as the engine works harder.
Practical thresholds
- Jeep JL/JT: regearing makes sense at 35s for most projects, mandatory at 37s
- Toyota 4Runner / Tacoma: 34s is usually the threshold for noticeable benefit
- Ford Bronco: 35s on non-Sasquatch, 37s on Sasquatch trims
If the truck is hunting between gears on the highway or struggling on grades that used to be effortless, gearing is usually the answer — not a tune.
Locker upgrades pair with regearing
Pulling the diff for a regear is the right time to add a selectable locker if it's on the plan. The labor is already done.
Differential, Axle & Driveline
Re-gears, lockers, axle upgrades, and driveline correction.
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