A Rubicon leaves the factory on 33-inch tires with 4.10 gears. You can bolt 35s on with a 2.5-inch lift. 37s require gearing, fender modification, possibly brake upgrades, and a hard look at the payload math — the Rubicon's already tight at 1,200 lb. Do this upgrade with your eyes open.
Rubicon: 33-inch LT285/70R17 mud-terrains, 4.10 axle gears, Rock-Trac 4:1 transfer case.
Sport/Willys: 32-inch LT255/75R17 all-terrains, 3.73 axle gears.
Mojave: 33-inch Falken Wildpeaks, 3.73 axle gears.
The Rubicon's 4.10 gears are designed for 33-inch tires. The relationship between tire size and gear ratio determines how hard the engine works at highway speed and how much torque multiplication you have in the lower ranges. Going to 35s on 4.10s is noticeable but livable. Going to 37s on 4.10s will strain the engine at highway speed, kill fuel economy, and put stress on the transmission.
With a 2.5-inch lift, 35-inch tires (315/60R17 or 35x11.5R17) fit a Gladiator without fender trimming. Most JT-specific 2.5-inch lift kits include the right hardware to clear this size. Stick with a proper JT-specific kit — the rear is leaf-sprung and requires JT-specific components, not JL parts.
The 4.10 gears on a Rubicon are borderline acceptable with 35s. If you highway-drive at freeway speeds regularly, budget for a re-gear to 4.56 or 4.88 when you put on 35s. It's not catastrophic without it, but the truck performs better with appropriate gearing.
37-inch tires change the build equation in several ways simultaneously:
**Gearing (mandatory):** 37s on 4.10 gears will make the Gladiator sluggish on highway, strain the drivetrain, and reduce fuel economy significantly. 4.56 is the minimum; 4.88 is better. The re-gear means pulling both front and rear differentials, installing new ring and pinion sets, and setting up lash and backlash correctly. This is a shop job unless you have a ring-and-pinion setup background.
**Lift:** 37s need 3–3.5 inches of lift for clearance. This moves the driveshaft angles beyond the factory range and requires a full-length JT-specific kit with control arm corrections. Long-arm kits improve the geometry further at this lift height.
**Fender trimming:** The JT Rubicon has plastic fender flares that extend 4 inches from the body. At full articulation with 37s, even with a 3-inch lift, the tire can contact the fender flare. The fix is trimming the inner fender well liner and possibly trimming the flare itself. This is a cut-and-not-uncut decision — verify fitment at full stuff before you cut.
**Brake consideration:** The factory brake system is sized for 33-inch tires. Going to 37s means more rotating mass and a longer lever arm to stop. The factory brakes can stop a stock truck on 37s, but stopping performance degrades. High-performance brake pads are a worthwhile addition before you start running 37s on trail.
**Payload impact:** The Rubicon already runs 1,200 lb payload. 37-inch tires weigh approximately 15 lb more each than 33s — that's 60 lb added to the unsprung rotating weight. Every pound of tire and wheel added reduces your available payload. On a Rubicon loaded for trail with passengers and gear, this math gets tight quickly.
| Part | Vendor | Est. price |
|---|---|---|
| 37-inch tire (e.g., 315/70R17 or 37x12.5R17) | BFGoodrich / Falken / Mickey Thompson / Nitto | ~$280 |
| Re-gear ring and pinion — front Dana 44 (4.88 ratio) | Yukon Gear / Motive Gear / Nitro Gear | ~$320 |
| Re-gear ring and pinion — rear Dana 44 (4.88 ratio) | Yukon Gear / Motive Gear / Nitro Gear | ~$320 |
| JT-specific lift kit (2.5" minimum for 35s; 3.5" for 37s) | Teraflex / Metalcloak / Skyjacker | ~$800 |
| Differential bearing kit (front and rear, for re-gear) | Timken / Motive Gear | ~$120 |
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.