Calculate theoretical road speed from engine RPM, gear ratio, final drive and tire rolling diameter.
Results are for information and preliminary estimation. For critical technical work, manufacturer data, local codes and qualified professional review take precedence.
Wheel RPM = engine RPM / (gear ratio × final drive). Speed = wheel RPM × tire circumference × 60. Real rolling diameter and drivetrain slip cause differences.
Example: At the same RPM, taller gearing or a larger effective tire diameter increases theoretical speed.
Automotive estimates are highly sensitive to driving conditions. For consumption, tire sizing and charging, the vehicle manufacturer’s approved limits remain the final reference.
Torque-converter slip, lockup and electronic ratio control can move real speed.
Calculate from tire size or use manufacturer rolling-circumference data.
How much will a trip cost in fuel?
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→What will the trip cost including fuel, tolls and extras?
→How different are two tire sizes in diameter and indicated speed?
→Tell us if a calculation is unclear, incomplete or appears incorrect.