The formula
crawl ratio = 1st gear × low range × axle ratio. Bigger tires make the gearing feel taller by the ratio of the diameters, so the axle ratio that matches your old gearing is current axle ratio × new tire ÷ old tire.
Crawl Ratio & Regear Calculator
Pick your transmission and transfer case, enter your axle ratio and tire sizes, and see your crawl ratio, the axle ratio that gets your gearing back on bigger tires, and what it does to highway RPM.
Drivetrain
Crawl ratio
40.7 : 1
4.01 × 2.72 × 3.73
Bigger tires and regearing
Crawl ratio on new tires
37.0 : 1
same gears, feels like this vs your current tires
Axle ratio to match current gearing
4.10
30.0 in to 33.0 in tires
With 4.56 gears
49.7 : 1
feels like 45.2 : 1 on your current tires
| At 65 mph in top gear | RPM |
|---|---|
| Now (3.73, 30.0 in) | 2,119 |
| New tires, same gears | 1,926 |
| New tires, 4.56 gears | 2,355 |
Tire sizes are nominal; real diameters run a little smaller, especially aired down. Automatic figures leave out torque converter multiplication. Example values are illustrative, not a specific Jeep.