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Will 40-inch tires fit a Jeep JK with a 4-inch lift?
Fitment answer · Updated October 27, 2026
Short answer
Only as a full build. 40s on a 4-inch JK need high-clearance or flat fenders, bump stops, low-backspacing wheels, stronger axles, steering upgrades and a deep regear.
Shop the gear for this build ↓ Tires, deflators and a compressor picked for this setup.
What you usually need
- Flat or high-clearance fenders and bump stops tuned for full stuff.
- Stronger axles or at least upgraded shafts and ball joints; stock JK axles struggle on 40s.
- Heavy-duty steering, brake upgrades and a reinforced spare carrier.
Regearing
40s on a JK usually call for 5.13 or 5.38 gears. Compare ratios in the Tire & Gear Calculator before you buy gears.
Compare
Gear for this build
- Mud-terrain tires (search) — Louder on the highway; buy for real mud use.
- Staun tire deflators — Repeatable trail pressures.
- VIAIR 88P portable compressor — Air back up before the highway.
- YUNPEAK 1.26" × 30' kinetic recovery rope — Bigger tires, bigger trails: carry recovery gear.
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FAQ
Do 40s fit a 4-inch JK?
Only with flat fenders and bump stops.
Do I need axle upgrades?
Usually yes.
Do I need to regear?
Yes, usually 5.13 or deeper.
Check your numbers
Use the free Tire & Gear Calculator to see speedometer error, highway RPM and a regear target, or ask TekJeep AI on the homepage with your year, trim, lift and wheel specs.
Related guides: All-terrain & mud-terrain tires · JK 2.5" lift overview
More fitment answers: 35s on a JK with a 2.5" lift · 33s on a stock JK · 37s on a JK with a 3.5" lift · 35s on a JK with a 3.5" lift · 33s on a JK with a 2.5" lift · 37s on a JK with a 4" lift · 35s on a stock JK · 37s on a JK with a 2.5" lift
Fitment disclaimer: Clearance depends on exact tire size, wheel specs, suspension and how hard you flex. Confirm with your tire shop or installer before buying.
Tire size how-tos: How to read a tire size · Bolt pattern & backspacing · Regearing for bigger tires · Tire pressure after upsizing · Speedometer error · Rubbing fixes