Dyno Numbers Explained: Crank vs Wheel Horsepower
Two cars can quote very different figures and still make the same real power.
Crank horsepower is measured at the engine; wheel horsepower is measured at the driven wheels after drivetrain losses. Always check which figure a claim uses before you compare.
Power figures only mean something when you know where they were measured. The gap between crank and wheel numbers causes a lot of confusion when people compare cars.
What each number measures
Crank horsepower is the power produced at the engine crankshaft, often quoted by manufacturers and engine dynos. Wheel horsepower, sometimes written as whp, is what reaches the driven wheels and is read on a rolling-road dyno. Wheel figures are always lower because power is lost getting there.
Why drivetrain loss varies
Between the crank and the wheels sit the gearbox, clutch or torque converter, driveshafts and, on many cars, a differential. Each absorbs some power through friction and by driving spinning parts. All-wheel-drive cars generally lose more than rear or front-wheel-drive cars because there is more hardware to turn.
Comparing figures fairly
A crank number and a wheel number are not interchangeable. Some quotes apply a correction factor to estimate crank power from wheel readings, and those estimates vary between dynos and operators. When you compare cars, make sure the numbers are the same type and, ideally, from a similar dyno.
The conditions that matter
- ✓Check whether a figure is crank or wheel before comparing two cars.
- !Drivetrain losses differ by layout, so a fixed percentage is only a rough guide.
- !Dyno type and conditions affect readings, so trends matter more than single numbers.
General guidance only. Details vary by exact vehicle and change over time; confirm with a reputable tuner before modifying.