Final Drive Ratio Calculator

Overall ratio (gear × final drive) and road speed at a given RPM — compare final drives before you swap.

Formula

Speed = [Engine RPM / (Gear ratio × Final drive ratio)] × Circumference × 60 / 1 000 000

Assumptions

If no tire size is entered, a common size is used as a worked example.

How to read it

A shorter final drive (higher ratio) accelerates better but spins the engine faster on the highway; a taller one lowers cruising revs and fuel use. Compare speed at the same RPM before and after to size the effect.

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