: How is the Horsepower of a car measured? And how did they measure it for the firsts motored cars?

Question

: How is the Horsepower of a car measured? And how did they measure it for the firsts motored cars?

In: Engineering

Answer 1

You don’t measure horsepower. You measure torque, the turning force on the crank shaft. Then you put that into an equation with current rotations per minute the engine is running to get horsepower:

horsepower = torque x rpm/5252

So all you need is something to measure torque and something to measure the rpm of the engine, and you get horsepower. This is why horsepower on a car is a curve, with it only achieving that highest horsepower for a small part of it.

Now that would be shaft horsepower. To measure at the wheels you put the car on a dynamometer, which is like a treadmill for cars, then measure the torque the tires apply to the rollers while the car is at various rpms. This will always be lower than shaft horsepower due to power losses in the transmission and the rest of the drivetrain.