Best Gear Ratio for 37s on a Jeep Wrangler JL, by Trim and Engine
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For most JL Wranglers with the 8-speed automatic, 4.88 is the gear ratio for 37s. It puts a 37x12.50R17 at almost exactly the gearing Jeep itself chose for its factory 35-inch Xtreme 35 package (4.56 on LT315/70R17s): about 2,170 rpm at 70 mph in 8th versus 2,150 from the factory.
A 4.56 only brings back the stock Rubicon-on-33s feel. Go 5.13 if you run a 3.6 with the 6-speed manual or a heavy, armored rig. On a 392, 4.56 or 4.88 both work. The table below gives the exact ratio for each factory setup.
The ratio that matches your factory gearing on 37s
"Matching" means the engine turns the same rpm at a given speed as it did from the factory, so shift points, passing power and highway cruising feel stock again. The math is simple: factory axle ratio × factory tire revs per mile ÷ new tire revs per mile.
| Factory setup | Factory axle ratio | Factory tire (Jeep revs/mile) | Ratio that matches on 37s | Stock gears act like on 37s |
|---|---|---|---|---|
| Sport, Sport S | 3.45 | P245/75R17 (666) | 4.04 | 2.95 |
| Sahara | 3.45 | P255/70R18 (650) | 3.94 | 3.02 |
| Sport S 4xe, Sahara 4xe | 3.73 | 20-inch factory tire (652) | 4.27 | 3.26 |
| Rubicon, Willys, Rubicon 4xe, Willys 4xe | 4.10 | LT285/70R17 KO2 (637) | 4.59 | 3.66 |
| Xtreme 35 package, Rubicon 392, Moab 392 | 4.56 | LT315/70R17 KO2 (604) | 4.84 | 4.30 |
| Rubicon 3.6 manual with optional 4.88 | 4.88 | LT285/70R17 KO2 (637) | 5.46 | 4.36 |
| 2023 EcoDiesel, 2023 Rubicon 392 | 3.73 | LT285/70R17 KO2 (645) | 4.23 | 3.29 |
Every factory tire figure in this table is the revolutions-per-mile number Jeep prints in its spec sheets, not the size molded on the sidewall. Jeep's 2023 and 2026 sheets list the same LT285/70R17 KO2 at 645 and 637 revs per mile, so I used each year's own number rather than averaging them.
For the 37, the table uses the BFGoodrich KO2 37x12.50R17 at 569 revs per mile, the same tire family Jeep fits at the factory. Other 37x12.50R17s list 564 to 566, which moves these results by less than 1%.
Why 4.88 is the answer for most JLs
The pure match from a Rubicon's 4.10 is 4.59, so on paper 4.56 is enough. But a 4.10 Rubicon on 33s is the tallest-geared of Jeep's Rubicon setups.
When Jeep put 35s on the Rubicon for the Xtreme Recon package, it didn't keep that ratio. It went to 4.56, deeper than the 4.32 a straight match from 4.10 would need on those tires.
Carry Jeep's own Xtreme 35 gearing over to 37s and you need 4.84, so 4.88 is the closest ratio you can buy. That's also what one Jeep regear shop's JL gear ratio chart lists for 37s on both the 3.6 and the 2.0 turbo with the 8-speed.
The chart shows why stock 4.10s feel so flat on 37s. At 70 mph in 8th they turn about 1,824 rpm, barely above a base Sport on highway tires, in a Jeep that's now heavier and taller. That's why the 8-speed keeps dropping out of 8th on grades.
A 4.88 lands between the factory Rubicon (2,041 rpm) and the factory Xtreme 35 (2,153 rpm) setups at highway speed. That's why it drives like a stock Jeep rather than a modified one.
Cruise RPM and crawl ratio by gear set on 37s
Every JL 8-speed (the 850RE behind the 2.0 and 3.6, the 8HP75 behind the 392 and the 4xe's 8P75PH) uses a 4.71 first gear and a 0.67 eighth. The 6-speed manual runs 5.13 first and 0.72 sixth. Rock-Trac transfer cases have a 4.0:1 low range; Command-Trac and Selec-Trac have 2.72:1.
| Axle ratio on 37s | 8-speed, 8th at 70 mph | 8-speed, 8th at 75 mph | Manual, 6th at 70 mph | Crawl ratio, 8-speed + Rock-Trac | Crawl ratio, 8-speed + 2.72 low | Crawl ratio, manual + Rock-Trac |
|---|---|---|---|---|---|---|
| 4.10 (stock Rubicon) | 1,824 rpm | 1,954 rpm | 1,960 rpm | 77.2:1 | 52.5:1 | 84.1:1 |
| 4.56 | 2,028 rpm | 2,173 rpm | 2,179 rpm | 85.9:1 | 58.4:1 | 93.6:1 |
| 4.88 | 2,170 rpm | 2,326 rpm | 2,332 rpm | 91.9:1 | 62.5:1 | 100.1:1 |
| 5.13 | 2,282 rpm | 2,445 rpm | 2,452 rpm | 96.6:1 | 65.7:1 | 105.3:1 |
| 5.38 | 2,393 rpm | 2,564 rpm | 2,571 rpm | 101.4:1 | 68.9:1 | 110.4:1 |
You can sanity-check the crawl column against Jeep's own numbers. A factory Rubicon automatic with 4.10s works out to 77.2:1, and Jeep advertised the 6-speed manual with optional 4.88s as a 100:1 crawl ratio; the formula gives 100.1:1.
Crawl ratio ignores tire size, though. A 37 that rolls 35.4 inches is about 12% taller than the factory LT285 (31.7 inches by Jeep's revs-per-mile figure), so any crawl ratio feels roughly 12% taller on 37s than the same number on stock tires.
JL 37s gear calculator
Pick your factory setup, then enter your new tire's revs per mile from the maker's spec sheet. The calculator shows the ratio that matches your factory gearing, plus cruise rpm and crawl ratio for each common gear set.
37x12.50R17: 564 to 569 on tire makers' spec sheets. No figure? Use 20,168 ÷ the tire's loaded height in inches.
The factory presets use Jeep's published ratios and tire revs per mile from the spec sheets linked above. RPM is mph × axle ratio × top gear × revs per mile ÷ 60, and crawl ratio is first gear × low range × axle ratio, so the results are estimates for a locked converter on a fresh tire.
Running something other than 37s, or starting from a non-Jeep vehicle? The general regear calculator for any tire size and axle ratio works from sidewall sizes, and the tire size calculator shows diameter and speedometer error for any swap.
How to choose: 4.56, 4.88 or 5.13
Start with the drivetrain, because the 8-speed and the manual behave differently. The 8-speed's two overdrive gears (0.84 and 0.67) let it carry deep axle gears on the highway. The manual's top gear is 0.72, so the same axle ratio spins it about 7% faster at speed.
| Your JL and how you use it | Ratio for 37s | Why |
|---|---|---|
| 2.0T or 3.6, 8-speed, daily driven, moderate armor | 4.88 | Matches Jeep's factory Xtreme 35 gearing; shop chart pick |
| 2.0T or 3.6, 8-speed, 300+ lb of armor or gear, frequent towing, rock crawling | 5.13 | One step deeper for each 300 lb added, per the shop rule of thumb |
| 3.6 with 6-speed manual | 5.13 | Shop chart pick for the manual on 37s |
| Rubicon manual already on factory 4.88 | 5.38 | Matching factory 4.88 gearing on 37s takes 5.46 |
| Rubicon 392 or Moab 392 (6.4 V8) | 4.56 or 4.88 | 4.56 per the shop chart; 4.88 matches Jeep's 4.56-on-35s gearing |
| Sport or Sahara on 3.45, mostly highway | 4.10 at minimum | 4.04 restores stock gearing, which is already highway-tall; the shop chart lists 4.88 by engine |
Here's a useful way to judge 5.13 on an 8-speed: 5.13 × 0.67 in 8th gives an overall 3.44, almost identical to 4.10 × 0.84 in 7th (3.44). So a 5.13 Jeep cruising in 8th on 37s turns the same rpm as a stock Rubicon on 37s held in 7th.
If 7th gear on your current setup already feels too busy at your cruising speed, stop at 4.88. If it feels fine, 5.13 gives you more pull for towing and crawling without much highway penalty.
Why sidewall sizes overstate the change
Most gear charts divide 37 by 33 (or 32.7, the nominal height of an LT285/70R17). That's a 13% jump. By revs per mile, the real change is smaller: 637 ÷ 569 = 1.12, so about 12%.
The reason is that a loaded tire rolls on a radius shorter than its unloaded height. Divide 20,168 by revs per mile and you get the "rolling" diameter: 31.7 inches for Jeep's LT285 KO2 and 35.4 inches for a 37x12.50R17 KO2. Neither tire actually rolls at the size printed on it.
That one-point gap is why charts built on nominal sizes push Rubicon owners toward slightly deeper gears than a true match. It doesn't change the 4.88 answer, but it explains why 4.56 lands so close to stock Rubicon gearing in the table above.
What a JL regear involves and costs
A regear replaces the ring and pinion in both axles, with new bearings and shims set up for correct backlash and tooth contact. Front and rear must end up at the same ratio on a 4x4, so it's always a two-axle job.
For price, one Jeep regear shop publishes $2,300 for a JL and $50 more for a Rubicon, covering both axles, ring and pinion, install kits, new front seals, fluids and reprogramming for tire size. Labor rates vary a lot by region, so get an itemized quote that covers both axles.
If you're buying parts for a shop to install, ring-and-pinion sets are axle-specific (front and rear differ, and not every JL trim uses the same axle models). Search for your exact axle, like this Yukon JL Dana 44 4.88 ring and pinion search on Amazon, and have your installer confirm fitment before ordering.
Reprogram tire size and axle ratio
After a regear on bigger tires, the JL's tire size and axle ratio settings have to be updated or the speedometer and odometer will read wrong. Dealers can do it, and so can plug-in tools such as the AEV ProCal SNAP for JL and JT (check the current price on Amazon).
One catch for newer Jeeps: AEV notes that certain 2025 and 2026 Wranglers were built with a driver-assistance module calibration that can't accept a new tire size with any dealer or aftermarket tool. If yours is one, the fix is a Stellantis customer bulletin at the dealer, so check before you regear.
Break-in and towing limits
New gears need a break-in: short drives with full cool-downs, no towing, no off-roading and no highway speeds at first, then a gear-oil change. Follow your installer's or gear maker's exact procedure; the Exodus 4x4 checklist is a typical example.
Don't expect deeper gears to raise your tow rating. Jeep's 2026 spec sheet rates a Rubicon with the 4.56 axle (the Xtreme 35 package) at 3,500 lb maximum trailer, versus 5,000 lb for the 4.10 automatic. See the full Wrangler towing capacity by year and configuration before you hook up a trailer on 37s.
37s on a JL: gear ratio questions
Can I run 37s on stock 4.10 gears?
It will move, but on 37s 4.10s act like 3.66s, close to a base Sport's highway gearing on a Jeep that is now heavier and taller. At 70 mph in 8th it turns about 1,824 rpm, so expect frequent downshifts on grades and weak passing power.
Is 4.56 enough for 37s on a Rubicon?
For a light, mostly stock Rubicon, 4.56 restores the factory Rubicon gearing almost exactly (4.59 is the match). It won't feel like Jeep's own 35-inch package, which is geared deeper. Add a steel bumper, winch and roof tent, and 4.88 is the safer choice.
4.88 or 5.13 for 37s with the 8-speed?
4.88 for a daily driver with moderate armor; 5.13 if you've added 300 lb or more, tow often or spend a lot of time crawling. At 70 mph in 8th, the difference is about 110 rpm (2,170 vs 2,282).
Does the Xtreme Recon package need a regear for 37s?
The factory 4.56 acts like a 4.30 on 37s. Matching Jeep's own gearing takes 4.84, so 4.88 is the usual step. On a 392, the shop chart keeps 4.56 for 37s, so staying put is a reasonable choice there.
Do 37s fit without other changes?
Gears are only one part. You'll also need lift and wheels with the right offset. And only the bigger tires raise axle clearance; the lift doesn't. See wheel offset and backspacing for big tires on a Wrangler and Wrangler ground clearance by trim and tire size.
I'm Suryashankar Dasgupta, the founder of Off-Road Handbook. I've been off-roading for years in the USA, including California and Texas, and have ridden mountain and desert terrain abroad. I've also driven a Jeep Compass for more than seven years, so I know the day-to-day side of Jeep ownership first-hand, from the Uconnect screen to the warning lights. Every guide here is researched from manufacturer owner's manuals, NHTSA recall and service-bulletin records and other trusted sources, checked against them before it is published, and corrected when we find a mistake. You can read how we work in our editorial policy: https://offroadhandbook.com/editorial-policy/
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