Formula
To calculate crank HP from WHP, you divide by the efficiency factor rather than adding a percentage back on.
Worked Example
This calculator provides estimates based on standard mathematical formulas. Real-world results will vary based on mechanical condition, environmental factors, and other variables.
Frequently Asked Questions
Yes, essentially. Both are measured at the engine crankshaft before the drivetrain.
Flywheel (or crank) horsepower is power measured at the engine's output before any drivetrain losses. It's the figure manufacturers usually advertise.
Divide wheel horsepower by (1 minus the drivetrain loss fraction). For a RWD car with 15% loss, divide wheel HP by 0.85.
Because the drivetrain — transmission, driveshaft, and differential — absorbs power through friction before it reaches the wheels, typically 10–25% depending on layout.
Wheel horsepower is directly measured on a chassis dyno, so it's the real number. Flywheel horsepower is an estimate derived from it using an assumed loss percentage.