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Automotive

Gear Ratio Calculator

Axle ratio from tooth counts, and overall drive ratio.

Your measurementsEvery assumption editable01

The ratio of the gear you are in. Direct drive is 1.00.

Drive ratioCalculated live02

Result

3.73: 1 axle

3.73:1 axle — 3.73:1 overall

Ring gear
41 teeth
Pinion gear
11 teeth
Axle ratioring divided by pinion
3.727:1
Transmission ratio
1:1
Overall ratioengine turns per axle turn
3.727:1

A numerically higher ratio means more torque multiplication and lower top-end gearing — a 4.10 accelerates harder and cruises at higher revs than a 3.23. Neither is better in the abstract; it depends on tyre size and how the vehicle is used.

Changing to taller tyres effectively lowers the numerical ratio. Fitting substantially larger tyres without re-gearing is the most common cause of a truck that suddenly feels gutless and hunts between gears.

The stamped ratio on the differential tag is the reliable source. Counting teeth is the check when the tag is missing or the axle has been changed.

Ring gear teeth divided by pinion teeth gives the axle ratio. Multiply by the transmission gear you are in and you have the overall ratio — how many times the engine turns for one turn of the axle.

Why use this tool?What it does differently03

Why use this tool?

From tooth counts

The reliable method when the differential tag is missing or the axle has been swapped.

Overall ratio too

Axle ratio through any transmission gear, which is what actually determines revs at speed.

Explains the trade-off

Numerically higher means more torque multiplication and higher cruising revs. Neither direction is better in the abstract.

Tyre interaction flagged

Taller tyres effectively lower the numerical ratio, which is why re-gearing follows a lift.

How this worksThe method04

How this gear ratio calculator works

Axle ratio is ring gear teeth divided by pinion teeth. A 41-tooth ring on an 11-tooth pinion gives 3.73:1 — the pinion turns 3.73 times for each turn of the ring gear and therefore of the axle.

Overall ratio multiplies that by the transmission ratio for the gear in question. In a direct-drive gear of 1.00 the overall equals the axle ratio; in an overdrive of 0.70 it drops well below.

A numerically higher ratio multiplies torque more and gears the vehicle shorter — quicker acceleration, higher revs at a given speed. Fitting substantially taller tyres has the same effect as fitting a numerically lower ratio, which is why a lift without re-gearing leaves a truck feeling gutless.

How to use itStep by step05

How to use it

  1. Step 1: Count the ring gear teeth

    Or read the ratio from the differential tag if it is still present.

  2. Step 2: Count the pinion teeth

    The smaller gear driven by the driveshaft.

  3. Step 3: Enter the transmission ratio

    For the gear you want to analyse. Top gear is often an overdrive below 1.00.

  4. Step 4: Check against tyre size

    If you have changed tyre diameter, the effective ratio has moved with it.

Example usageWorked figures06

Example usage

A common truck axle
41 ring teeth over 11 pinion teeth gives 3.727:1. In a 0.70 overdrive that is 2.609:1 overall.
A performance ratio
41 over 10 gives 4.10:1 — noticeably shorter gearing, quicker off the line, higher cruising revs and worse economy.
Economy gearing
37 over 11 gives 3.364:1. In a 0.65 overdrive that is 2.186:1 overall, which is where long-legged highway cruising comes from.
Frequently asked questionsCommon questions07

Frequently asked questions

How do I calculate gear ratio?

Divide the ring gear tooth count by the pinion tooth count. A 41-tooth ring on an 11-tooth pinion gives 3.73:1.

Is a higher gear ratio better?

Neither is better in the abstract. Numerically higher multiplies torque more and accelerates harder but raises cruising revs and costs fuel. Numerically lower does the reverse.

Do I need to re-gear after fitting bigger tires?

Often yes. Taller tyres act like a numerically lower ratio, so a substantial increase can leave a vehicle sluggish and hunting between gears. Re-gearing restores the original effective ratio.

What is overall drive ratio?

Axle ratio multiplied by the transmission ratio for the gear you are in. It tells you how many engine revolutions produce one axle revolution.

Where do I find my axle ratio?

Usually stamped on a tag at the differential cover, or encoded in the vehicle's build sticker. Counting teeth is the fallback when neither survives.

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