Continental Europe Tax Horsepower Systems
For much of the 20th century, European governments utilized tax horsepower—an administrative unit used to determine vehicle registration taxes—rather than actual brake horsepower. While these systems shared a common goal of taxing more powerful vehicles, the formulas varied significantly across borders, often influencing how manufacturers designed their engines.
In the decades leading up to World War II, several continental countries used calculations similar to the British system. However, because continental Europe used millimeters for cylinder dimensions while Britain used inches, rounding differences occurred. Consequently, one British tax horsepower unit was equivalent to 1.014 continental (specifically French) tax horsepower units.
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Key Facts
- Administrative Purpose: Tax horsepower is a legal calculation used for registration and taxation, not a measure of actual engine performance.
- France: Used the Cheval Fiscal (CV), evolving from engine dimensions to CO2 emissions by 1998.
- Germany: Introduced Steuer-PS in 1906, basing it on overall engine displacement.
- Belgium: Simplified taxation to 1 tax horsepower for every 200 cubic centimeters (cc) of engine capacity.
- Italy & Spain: Continued using fiscal horsepower for insurance and taxation, often influencing the use of turbochargers to keep displacement low.
France: The Evolution of the Cheval Fiscal
The Cheval Fiscal (CV), meaning "steam horses," is the administrative unit used for French registration certificates, known as cartes grises (grey cards). This system has undergone several major revisions since its inception on January 1, 1913.
The Original and 1956 Formulas
Initially, the CV was calculated using the number of cylinders, cylinder bore, stroke, maximum engine speed, and a coefficient based on the number of cylinders. By 1956, the formula was simplified. For petrol engines, the administrative power (P) became a product of displacement (C) and a constant (K = 5.7294). Diesel engines, wood gas vehicles, and CNG vehicles received a 0.7 multiplier, resulting in a constant of 4.0106.
The Citroën 2CV is a famous example of this system, as its name literally refers to its two tax horsepower rating.
The 1978 and 1998 Revisions
In 1978, France introduced a more complex system based on the theoretical speed of the vehicle at 1,000 rpm across various gears. This calculation accounted for different transmission types, including manual, automatic, and CVT (Continuously Variable Transmission).
By 1998, the system shifted toward environmental impact. The fiscal tax was calculated based on standardized carbon dioxide (CO2) emissions in grams per kilometer (g/km) and the maximum engine power in kilowatts (kW), using data from the European certificate of conformity.
Germany: Steuer-PS and Economic Policy
Germany introduced Steuer-PS on June 3, 1906. Unlike the French system, it was based on overall engine displacement. To account for efficiency differences, two-stroke engines were taxed at a higher rate than four-stroke engines because two-stroke cylinders fire every revolution, whereas four-stroke cylinders fire every second revolution.
In 1933, the government abolished the annual car tax to stimulate the auto industry, leading to a massive surge in production between 1932 and 1938. While Steuer-PS returned after 1945, the introduction of road fuel taxes in 1951 eventually made the annual car tax less significant than fuel-based taxation.
Southern Europe: Italy and Spain
In Italy, fiscal horsepower is still utilized for insurance purposes. Historically, heavy taxes on engines larger than 2,000 cc following the 1973 oil crisis encouraged Italian manufacturers to use turbochargers to increase power without increasing displacement.
Spain's Potencia fiscal is defined by overall engine capacity, favoring four-stroke engines over two-stroke engines. For vehicles where standard formulas do not apply, such as electric vehicles, the tax is derived from the effective engine power—the maximum power provided after 30 minutes of full-power use.
Switzerland: A Fragmented System
Switzerland's 26 cantons historically employed various taxation methods. While many originally used a tax horsepower formula based on cylinder bore and stroke, the system diverged over time. By 1973, Berne switched to vehicle weight, and by 1986, Ticino used a combination of engine size and weight. As of 2022, Geneva was the only canton still basing road tax purely on tax horsepower.
Summary of European Tax Horsepower Approaches
| Country | Primary Metric | Key Characteristic |
|---|---|---|
| Belgium | Cubic Capacity | 1 CV per 200 cc |
| France | Mixed / Emissions | Shifted from dimensions to CO2 emissions in 1998 |
| Germany | Displacement | Higher rates for two-stroke engines |
| Italy | Displacement | Used primarily for insurance; influenced turbocharging |
| Spain | Engine Capacity | Uses "effective power" for electric vehicles |
| Switzerland | Various | Canton-specific; varies by weight or displacement |
Frequently Asked Questions
What is the difference between tax horsepower and actual horsepower?
Tax horsepower is an administrative value used by governments to determine tax brackets and registration fees. It is calculated using formulas based on engine dimensions or emissions, whereas actual horsepower (brake horsepower) measures the real mechanical power produced by the engine.
Why did Italy's tax system lead to more turbochargers?
Because Italian taxes were heavily imposed on engines with a displacement larger than 2,000 cc, manufacturers used turbochargers to increase the engine's power output without increasing the physical size (displacement) of the engine.
How did France change its car tax in 1998?
France moved away from engine dimensions and instead based the fiscal tax on a combination of the vehicle's CO2 emissions (g/km) and its maximum engine power in kilowatts (kW).
How did Germany treat two-stroke engines differently?
Germany applied a higher tax horsepower factor to two-stroke engines (0.45) compared to four-stroke engines (0.30) because two-stroke cylinders have a power stroke every revolution, making them theoretically more powerful for the same displacement.
Which Swiss canton was the last to use pure tax horsepower?
As of 2022, Geneva was the only Swiss canton that still based its road tax purely on tax horsepower, while others had moved to weight-based or mixed systems.