About this tool
The Wheel HP ↔ Crank HP Calculator converts between the power measured at the wheels on a chassis dyno and the power produced at the crankshaft (flywheel). Manufacturers quote crank horsepower, but a rolling-road dyno can only read what reaches the tires — the difference is drivetrain loss, the power absorbed by the transmission, differential, driveshafts, and rotating mass.
The relationship is Crank HP = Wheel HP / (1 − loss) and, going the other way, Wheel HP = Crank HP × (1 − loss). The tool estimates the loss fraction from your drivetrain: front-wheel drive around 10%, rear-wheel drive around 15%, and all-wheel drive around 22%, with roughly an extra 4% added for an automatic transmission because of torque-converter and pump losses. You can override all of this with a custom loss percentage if you know your specific figure. The same math applies equally to torque.
Everything runs locally in your browser. Treat the result as an estimate: real drivetrain loss is not a fixed percentage — it varies with gear, load, temperature, tire, and driveline design, and the popular "15% RWD" rule is a convention, not a law. Use it to compare builds or sanity-check a dyno sheet, not as a certified crank figure. When comparing two cars, make sure the same loss assumption is applied to both.