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April 22, 2007, at 03:23 AM
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See also WHP (wheel horsepower).
Car manufacturers typically specify horsepower as measured at the engine’s crankshaft. The horsepower measured at the wheels is typically 20% lower for all-wheel-drive cars and 10% lower for front- or rear-wheel-drive cars due to drivetrain losses.
Be suspicious of quoted crankshaft horsepower numbers from people who did not physically remove the engine from the car for measurement - drivetrain losses can be estimated, but estimates vary widely (in part because they are nonlinear and thus difficult to estimate). Converting wheel horsepower measurements to crank horsepower estimates provides a larger number, but it also adds a new variable to the formula (drivetrain loss) which makes the resulting number difficult to interpret.