Formula
Every gear, bearing, and fluid in a drivetrain consumes power. A car producing 400 HP at the engine (crank) will typically only put about 330-340 HP to the tires on a rear-wheel drive vehicle.
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
Crank HP is measured directly at the engine output shaft (what manufacturers advertise). WHP is measured at the wheels after the power has traveled through the transmission, driveshaft, and axles.
FWD is generally more efficient (10-15% loss) because it has fewer components and no long driveshaft compared to RWD (15-18% loss).
Wheel horsepower is the power actually delivered to the ground, measured on a chassis dyno after drivetrain losses. It's lower than the engine's crank horsepower.
Roughly 10% for front-wheel drive, 15% for rear-wheel drive, and 20–25% for all-wheel drive, with automatics generally losing a little more than manuals.
Advertised figures are crank horsepower; a chassis dyno reads wheel horsepower after drivetrain losses, so a lower number is normal and expected.