Gear Ratio For Vehicle Calculator

Work out gear ratio for vehicle instantly with clear inputs, formula shown and shareable results.

About Gear Ratio For Vehicle Calculator

Road speed is engine rpm divided by the overall ratio (gearbox times final drive), times tyre circumference. Speed per 1000 rpm in top gear is the single most useful gearing figure: 35-45 km/h is typical for a relaxed motorway cruiser.

Formula

Gearing

wheel rpm = engine rpm / (gear ratio x final drive); speed = wheel rpm x circumference x 60 / 1e6

Worked example

With the default values below, Gear Ratio For Vehicle Calculator returns Road speed of 92.76. Change any input above and every figure here is recalculated in your browser.

Inputs used

Engine speed: 2,500 rpm
Gearbox ratio: 0.85 :1
Final drive ratio: 3.9 :1
Tyre rolling circumference: 2,050 mm

Results

Road speed: 92.76 km/h
Overall ratio: 3.32 :1
Wheel speed: 754.15 rpm
Speed per 1000 rpm: 37.10 km/h

Step by step

1Values used
2Gearing
3Road speed= 92.76 km/h
4Overall ratio= 3.32 :1
5Wheel speed= 754.15 rpm
6Speed per 1000 rpm= 37.10 km/h

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What is a good top gear ratio?

One giving 35-45 km/h per 1000 rpm, so 100 km/h sits at 2,200-2,800 rpm — near peak efficiency without losing all flexibility.

Why change the final drive?

A shorter final drive improves acceleration at the cost of cruising rpm and economy. It is the cheapest way to alter the whole gearing set.