Gear Ratio Calculator
Find the axle ratio that restores performance after bigger tires, with rpm and crawl ratio.
Transmission & cruise (for rpm and crawl ratio)
| Axle ratio | Feels like (stock tires) | RPM at cruise | Crawl ratio | vs stock |
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How to use the gear ratio calculator
Enter your stock tire size, your new tire size and the axle ratio your truck has now. You can type a size like 265/70R17 or just the diameter in inches. The calculator shows the ratio that would restore stock performance and the closest common ring-and-pinion ratio.
The math
Bigger tires act like taller gears. The ratio that restores the original feel is your current ratio × new tire diameter ÷ old tire diameter. For example, 3.73 gears with 31-inch tires going to 35s: 3.73 × 35 ÷ 31 ≈ 4.21, so a 4.10 or 4.30 set is the usual choice.
RPM and crawl ratio
Engine rpm at cruise is mph × axle ratio × top-gear ratio × 336 ÷ tire diameter. Open the transmission section to enter your own top gear, first gear and low-range ratios from your owner's manual or the manufacturer's spec sheet. Crawl ratio is first gear × low range × axle ratio.
Front and rear must match
On a 4x4, both axles need the same ratio. Mismatched gears will fight each other and damage the transfer case the moment you engage 4WD.
More detail: regearing after bigger tires and 4-High vs 4-Low.