JL Wrangler on 37s: Which Gear Ratio?

For a Jeep Wrangler JL (Sport / Sport S baseline: 3.45 gears on 31.5-inch factory tires), 37-inch tires need a 4.05 restore-stock ratio just to feel factory again. Here is every real candidate, judged.

Axle ratio	Crawl ratio	RPM @ 70 on 37s	Verdict
3.45	65.0:1	1,470	Highway-leaning — under restore-stock; expect downshifts and a lazy feel.
3.73	70.3:1	1,589	Highway-leaning — under restore-stock; expect downshifts and a lazy feel.
4.10	77.2:1	1,747	Factory manners — within a few percent of restore-stock.
4.56	85.9:1	1,943	Dual-purpose sweet spot — one honest step deeper than stock.
4.88	91.9:1	2,079	Trail-leaning — crawl-first gearing; cruise RPM is the price.
5.13	96.6:1	2,186	Trail-leaning — crawl-first gearing; cruise RPM is the price.
5.38	101.4:1	2,292	Trail-leaning — crawl-first gearing; cruise RPM is the price.

Crawl uses first gear 4.71 × the platform's deepest factory low range 4.00:1. Cruise RPM uses top gear 0.67 of the 850RE 8-speed automatic. Highlighted row: closest to restore-stock.

How to read this

Restore-stock (4.05) is the floor: it returns the exact RPM and response the truck had on its factory tires. Going less gear than that on 37s is borrowing against the transmission — it will downshift on grades and feel gutless in the passing lane. One step deeper than restore-stock is where most dual-purpose builds land: the crawl ratio climbs into genuinely useful territory and the cruise penalty is a few hundred RPM. Two steps deeper is a trail-first build that happens to drive home.

The other half of the decision

The ratio is the cheap part of this page. The expensive parts are everything attached to it: whether your carrier crosses a break at that ratio, whether a locker goes in while the diff is open, and what a shop should charge. That is the Decision System's job — it builds the parts list and budget for exactly this combination. Or run more candidates yourself in the regear comparison calculator.