The Belgian tax system has its oddities. One of them is what they call “fiscal horsepower”. It is an interesting but blunt tool to define which cars are fast, and therefore should be taxed higher than others.
Accelleration is the combination of power and mass of the object you want to move. Most cars that are known to be fast are known because of their higher rate of acceleration – most normal cars can do high speeds too, if you just wait long enough for it.
So the Belgian government came with a formula to figure this out in an easy to chart number: the fiscal horsepower of a car.
This number is calculated by the next formula:
(cilinder content in liters times 4) + (weight of the car divided by 400)
Just in case if anyone’s interested in figuring out how much taxes they need to pay on their next ride.
The Belgian tax people changed their formula, and scrapped the weight of the car out of it. All info is here.