Gear Ratio Calculator

Gear ratio = driven gear teeth ÷ driver gear teeth. For an axle, that is ring gear teeth ÷ pinion gear teeth — for example, 41 ring teeth ÷ 10 pinion teeth = 4.10, written as 4.10:1.

It means the driveshaft (pinion) rotates 4.10 times for every single rotation of the wheels (ring gear). The bigger the number, the more torque multiplication — and the higher the engine RPM at a given road speed.

Neither is universally better — it depends on the job. A numerically higher ratio (e.g. 4.10 vs 3.21) multiplies torque more, so acceleration and towing feel stronger, but cruise RPM is higher. A numerically lower ("taller") ratio drops cruise RPM for quieter highway driving and potentially better fuel economy, at the cost of off-the-line grunt.

Check the axle tag or option sticker first. If those are gone, remove the differential cover and read the tooth counts stamped on the ring gear (big number = ring teeth, small number = pinion teeth), then divide. You can also jack up one wheel, mark the tire and driveshaft, and count driveshaft rotations per tire rotation — with an open differential, rotate the tire two full turns and halve the driveshaft count.

Overdrive is any gear with a ratio below 1:1 — the output shaft spins faster than the input. A 0.70:1 overdrive with 4.10 axle gears gives a 2.87 final drive in top gear, which is why modern trucks cruise at low RPM on the highway despite deep axle gears.

Yes. Taller tires act like a taller (numerically lower) gear: effective ratio = old ratio × (new tire diameter ÷ old tire diameter). Going from 30-inch to 35-inch tires on 3.73 gears drops engine RPM about 14.3% at the same speed — the workload feels like roughly 4.35 gearing in reverse, which is why many owners "regear" to a numerically higher axle ratio to get the RPM back. Try the Tire-Change tab above.

Common OEM and aftermarket ratios run from about 2.47 up to 6.86, with popular stops at 3.08, 3.21, 3.42, 3.55, 3.73, 3.90, 4.10, 4.30, 4.56, 4.88, 5.13 and 5.38. See the reference chart on this page — and note that sets like 4.09 / 4.10 / 4.11 are nominally the same ratio cut with slightly different tooth counts.

Multiply the three stages: transmission gear ratio × transfer case ratio × axle ratio. Example: a 2.48 first gear × 1.00 high-range transfer case × 4.10 axle = 10.17 overall in first gear. Use the Combined tab above to run a whole gear set at once.

A gear ratio describes one gear pair. Crawl ratio is the total multiplication in low range — transmission first gear × transfer case low range × axle ratio — and describes off-road crawling ability. Our dedicated crawl ratio calculator covers that 4x4-specific case.

Yes — the speedometer typically reads from driveshaft speed, so changing the axle ratio or tire diameter makes it read wrong until recalibrated. After a regear, budget for a speedometer correction (a programmer, a speedometer gear, or a shop recalibration).

No. The set must be made for your specific axle model, and the tooth counts are only half the story — correct pinion depth, backlash and bearing preload determine whether the gears run quietly and survive. Gear setup is precision work; most owners have a driveline shop install the set.

Those are the inverse problems and they live in their own tools: the gear ratio to RPM calculator finds engine RPM from speed, tire size and ratio, and the gear ratio speed calculator finds road speed from RPM. This page stays focused on computing the ratio itself.

When power flows through several meshed pairs in series, the overall ratio is the product of each pair's ratio: (driven₁ ÷ driver₁) × (driven₂ ÷ driver₂) × … The Compound tab above solves trains like a 28→36, 30→34, 17→67 example, which works out to about 5.74:1.

No — it makes it quicker off the line, but each gear tops out at a lower speed and cruise RPM climbs. Top speed is limited by power, aerodynamics and redline; gearing just chooses where in the RPM band the engine operates.