What is overall gear ratio?

Overall ratio = gearbox ratio x final drive ratio. This determines how many engine revolutions produce one wheel revolution. Lower overall ratio (taller gearing) = higher speed per RPM but slower acceleration.

How do I find my gear ratios?

Gear ratios are in the workshop manual or can be found on enthusiast forums for your car. Common final drive ratios are 3.5-4.5 for most cars. First gear is typically 3.0-4.0, top gear is 0.7-1.0.

What is the ideal RPM for motorway cruising?

Most engines are most efficient at 1500-2500 RPM. At 70 mph, typical cars run 2200-3200 RPM. Lower RPM means less fuel consumption and less noise. A 6-speed gearbox typically achieves lower cruising RPM than a 5-speed.

What do gear ratios mean?

A gear ratio tells you how many times the input shaft rotates for each rotation of the output shaft. A ratio of 3.5:1 means the engine turns 3.5 times for every wheel rotation. Lower gears have higher ratios (more torque multiplication) and higher gears have lower ratios (more speed).

What is the final drive ratio?

The final drive ratio is the last gear reduction between the gearbox output and the wheels, located in the differential. A typical final drive ratio is 3.0-4.5:1. The overall gear ratio is the gearbox ratio multiplied by the final drive ratio. Changing the final drive ratio affects all gears equally.

CarCalcs

Gear Ratio Calculator

Calculate road speed at any RPM from gear ratio and tyre size.

Gear Ratio

Specific gear ratio

Final Drive Ratio

Tyre Circumference

Use Tyre Size Calculator

Engine RPM

How We Calculate This

Speed = (RPM / Overall ratio) x Tyre circumference, converted to mph/kph. Overall ratio = gear ratio x final drive ratio.

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Last updated: February 2026

All calculations are estimates. Actual figures may vary based on driving conditions, vehicle specifications, and other factors.