There's a difference between horsepower measured at the wheels and measured at the crank. I always thought of a true BHP value (at least as given by a car manufacturer as a spec) is measured at the crank. That is why a measurement at the wheel will always be a smaller value than specified for the car. The loss is more for automatics and less for manuals.

What happens if you have an all wheel drive vehicle? If the power is distributed to all four wheels in some fashion, then how do you get a total horsepower that is realistic?

Calvin