Gear Ratio Recommendations vs Tire Size
Larger tires require numerically higher gear ratios to keep effective drive ratio in the same range. Chart for the 4.0L automatic and manual XJ.
When you go to bigger tires, your effective drive ratio drops (taller tires = each axle revolution travels further). Without re-gearing, the engine bogs in higher gears and the transmission shifts late. Re-gearing restores the drive ratio.
XJ gear ratio guide for the 4.0L:
AUTOMATIC (AW4):
- 29" tires (stock): 3.55 to 3.73 stock gearing fine.
- 31" tires: 3.73 to 4.10. Stock 3.55 will be sluggish.
- 32" tires: 4.10 mandatory; 4.56 better.
- 33" tires: 4.56 ideal. 4.10 tolerable in flatlands.
- 35" tires: 4.88 ideal. 4.56 minimum.
- 37" tires: 5.13 or 5.38. Requires aftermarket case carriers.
MANUAL (AX5/AX15/NV3550):
- 29" tires: 3.55 stock fine.
- 31" tires: 3.73 to 4.10.
- 32" tires: 4.10.
- 33" tires: 4.56 best.
- 35" tires: 4.88 best.
- 37" tires: 5.13.
The AW4 automatic XJ benefits MORE from re-gearing than the manual because the torque converter loses efficiency with mismatched gearing. A 33" tire XJ with stock 3.55 gears (common) is dramatically improved with 4.56 re-gear.
Gear costs: Yukon gear sets ~$200/pair, master install kit $80, install labor at a gear shop $400-600 per axle. DIY install is doable with patience and the right tools. Pinion bearing preload and ring gear backlash are precision settings.
Both axles must match. If you re-gear, do both axles at once (or order both ratio matched).
Why it works
- Restores drivability with larger tires
- Improves trail crawl speed
- Reduces transmission heat
Trade-offs
- Gear install is precision work
- Cost ~$1000+ per axle if shop-done
- Must do both axles
Tools required
- ring & pinion tooth count
- calculator
Sources
Related
- Dana 30 ARB Air Locker
- Ford 8.8 Explorer Rear Axle Swap (Full Guide)
- All Jeep Cherokee XJ guides & tools
- Browse the full DIY database
Written and maintained by an AZ wheeler and driveway wrencher. How we source guides. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.