Crawl Ratio Calculator (first gear × low range × axle ratio, crawl speed)

Understanding the crawl ratio calculator — concept and principle

This calculator works out the crawl ratio of an off-road vehicle, the overall gear reduction in its lowest gear, and shows the resulting crawl speed, wheel rpm and wheel torque. Off-roaders use it when choosing axle gears, transfer cases or tyre sizes for rock crawling and steep descents.

Multiply every reduction: with the default inputs the result is 44.6:1 (13,382 N·m at the wheels).

How it is calculated

Crawl ratio = first gear ratio × transfer-case low ratio × axle ratio

Wheel rpm = engine rpm ÷ crawl ratio.
Crawl speed (km/h) = wheel rpm × π × tyre diameter (in) × 0.0254 × 60 ÷ 1000; mph = km/h ÷ 1.609344.
Wheel torque (no losses) = engine torque × crawl ratio.

The principle

Gears in series multiply. Each stage turns a fast, weak input into a slower, stronger output by its ratio, so the overall reduction is the product of all of them. A high crawl ratio lets the engine run at an easy speed while the wheels creep, giving fine control over rocks and strong engine braking downhill. Torque is multiplied by the same ratio, minus driveline losses. The tyre turns wheel rpm into road speed: one revolution moves the vehicle one circumference, π × diameter. Larger tyres therefore raise crawl speed and lower wheel force, which is why bigger tyres are often paired with lower (numerically higher) axle gears.

Worked example

Default inputs: first gear 4.0, low range 2.72, axle 4.10, 33 in tyres, 1,000 rpm, 300 N·m.

Crawl ratio = 4.0 × 2.72 × 4.10 = 44.6, written 44.6:1.
Wheel rpm = 1,000 ÷ 44.608 = 22.4.
Circumference = π × 33 × 0.0254 = 2.633 m.
Speed = 22.42 × 2.633 × 60 ÷ 1000 = 3.54 km/h = 2.2 mph.
Wheel torque = 300 × 44.608 = 13,382 N·m, before losses.

Each point is the calculator re-run with only “First gear ratio” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

First gear ratio	Crawl ratio (overall low gear)
1	11.2
2	22.3
3	33.5
4	44.6
5	55.8
6	66.9
8	89.2

How to read the result

A walking-pace crawl speed of about 2–3 km/h at idle gives good control. The wheel torque is shared by all driven wheels and is reduced by driveline losses, often around 10–20%.

Common mistakes

Adding ratios instead of multiplying them.
Using the tyre's nominal size when the real loaded diameter is smaller.
Forgetting that the automatic transmission's torque converter adds slip and multiplication.
Treating the no-loss wheel torque as usable traction; grip usually limits first.

Keep in mind: Very high crawl ratios multiply torque into the axles and shafts. Make sure the driveline is rated for it, and follow the manufacturer's limits.

Frequently asked questions

How do bigger tyres change the crawl ratio?

They lower the effective ratio in proportion to their diameter, raising speed and reducing wheel force.

How do I raise my crawl ratio?

Fit lower axle gears, a lower transfer-case range or a gearbox with a lower first gear.

Sources: Gear-train reduction: overall ratio of gears in series is the product of the individual ratios (e.g. R. L. Norton, Design of Machinery) · NIST Special Publication 811 (2008), Appendix B (1 in = 25.4 mm; 1 mile = 1.609344 km)

Checked 9 Nov 2026. Gear-train reduction: the overall ratio of gears in series is the product of the individual ratios; wheel speed from π × tyre diameter. Gear ratios, tyre size, rpm and torque are example values. 1 in = 25.4 mm; 1 mile = 1.609344 km.

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