Running 37s on a JK requires a minimum 3.5" lift, a regear to 4.88 or higher, and fender trimming on most non-Rubicon trims — get those three things right and a 37-inch JK is a genuinely capable trail rig.
The 37x12.5R17 is the standard "serious trail" tire size for the JK platform. At 3.5" of lift, 37s will fit most JK body variants but with limited fender clearance at full flex — the tire contacts the inner fender liner on Sport and Sahara models when the suspension compresses fully. At 4" of lift, you get full flex without contact on most trims without trimming. To get true full-flex fitment with zero rubbing on any JK variant, plan on 4" of lift plus trimming the inner fender well and removing the plastic fender liner trim piece above the wheel. The Rubicon, which comes with wider fender flares from the factory, fits 37s at 3.5" with less trimming needed. On 2007–2011 JKs, the front fender flare mounting tabs are a common trimming limitation — a grinder and patience get you there.
The BFG KM3 is the benchmark mud-terrain in this size — aggressive tread, strong sidewall for rock, and compound that balances wet performance better than most competitors. Nitto's Trail Grappler sits slightly below the KM3 in tread aggression but offers better ride quality and noise on pavement, making it the better pick for builds that see significant road miles. The Toyo Open Country MT is the budget option of the three — real-world performance is close to the KM3 on most terrain, and at $285 per tire it's $140 cheaper per set of five. All three are true load range E tires; buy five, not four — a spare matters more with larger tires on remote trails.
The regear requirement for 37s is not optional on any JK. Stock Sport and Sahara JKs come with 3.73 gearing — fine for the factory tires, completely inadequate for the added rotational mass and rolling resistance of 37s. At 3.73 with 37s, you'll lug at highway speed, overheat the transmission on grades, and lose low-end torque on the trail. The correct ratio for 37s on the JK is 4.88 — it restores effective drive ratio to near-stock and the difference in off-road crawl ratio is immediately apparent. Heavily built rigs on 37s in rock terrain sometimes run 5.13 for the additional mechanical advantage, but 4.88 is correct for the majority of builds.
Before mounting 37s, verify your current wheel backspacing. The JK needs 4.5"–4.75" backspacing to clear the upper control arm brackets with 37s at lift. If your wheels were spec'd for 33s, check before you mount — an extra $50 in new wheels beats grinding a bracket. Wheel spacers can solve backspacing issues, but dedicated wheels with correct backspacing are preferable for long-term hub and bearing health.
| Part | Vendor | Est. price |
|---|---|---|
| BFGoodrich Mud-Terrain T/A KM3 37x12.5R17 | BFGoodrich | ~$320 |
| Nitto Trail Grappler M/T 37x12.5R17 | Nitto | ~$295 |
| Toyo Open Country M/T 37x12.5R17 | Toyo Tires | ~$285 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.