The fuel consumption given in the characteristics of cars is an economic indicator for a given brand and is an important parameter when comparing vehicles. In real operating conditions it will differ from the catalog values given in the car characteristics. It should be remembered, that the real motion of the vehicle depends on many parameters that interact with each other, and above all, the technical condition of the car, the way it is driven by the driver, weather conditions, road condition, road traffic density, etc..
Comparison of catalog data with the results obtained during operation and a statement, that the actual data differs from the values given in the characteristics of the car, cannot be the basis for a complaint about the purchased vehicle. A complaint may only be justified, when the control measurement of fuel consumption will be carried out in accordance with the conditions set out in the applicable regulations and on an approved measuring stand, which in fact is practically impossible. Laboratories, where such measurements can be made, there are very few and they do not provide services to the general public, Moreover, the cost of testing one vehicle is several thousand dollars and requires a very tedious legal and organizational procedure.
Hence the following conclusion – fuel consumption given in the characteristics is an important parameter informing the buyer about the economy of the car, while actual fuel consumption may vary by up to 2 dm3na 100 km.
Finally, a few remarks, how to operate a car, so that driving is economical, economic. The operating conditions of the car can be considered in three aspects – the driver, car and road.
We can assume, that the driver in approx. 70% has an impact on the economy of driving, car in approx. 20%, and the road in approx. 10%. The driver decides how to drive and how dynamically it is, i.e. about accelerations, the correct use of the gear ratio, proper engine speed or braking method. Especially the operation of the car according to the principle of "gas – brake ”is definitely not recommended due to its economical fuel consumption.
I think, that this article cleared many doubts, what car users encountered when confronting the entries given in vehicle manuals with the calculated actual values of fuel consumption achieved by the used vehicle.