Bronco on 37s: Which Gear Ratio?

For a Ford Bronco (6th gen) (Badlands manual baseline: 4.70 gears on 32.7-inch factory tires), 37-inch tires need a 5.32 restore-stock ratio just to feel factory again. Here is every real candidate, judged.

Axle ratio	Crawl ratio	RPM @ 70 on 37s	Verdict
3.73	75.2:1	1,532	Highway-leaning — under restore-stock; expect downshifts and a lazy feel.
4.27	86.1:1	1,754	Highway-leaning — under restore-stock; expect downshifts and a lazy feel.
4.46	89.9:1	1,832	Highway-leaning — under restore-stock; expect downshifts and a lazy feel.
4.70	94.7:1	1,931	Highway-leaning — under restore-stock; expect downshifts and a lazy feel.
4.88	98.4:1	2,005	Highway-leaning — under restore-stock; expect downshifts and a lazy feel.
5.13	103.4:1	2,107	Factory manners — within a few percent of restore-stock.
5.38	108.5:1	2,210	Factory manners — within a few percent of restore-stock.

Crawl uses first gear 6.59 × the platform's deepest factory low range 3.06:1. Cruise RPM uses top gear 0.65 of the Getrag MT88 7-speed manual (C + 1-6). Highlighted row: closest to restore-stock.

How to read this

Restore-stock (5.32) 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.