Calculate theoretical road speed from engine RPM, gear ratio, final-drive ratio and tyre size.
Worked example
At 3,000 RPM with a 1.000 gear, 3.55 final drive and 235/40 R18 tyres, the calculator gives the theoretical speed before slip or tyre deformation.
Why actual speed can differ
Tyre rolling radius changes under load, torque converters may slip, clutches can slip and automatic transmissions may have additional behaviour not represented by a simple fixed ratio.
Useful for gearing comparisons
Change the final drive, tyre size or gear ratio independently to see which change has the largest effect on cruising RPM or theoretical speed.
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