If you’ve been keeping track of the amount of fuel your car goes through on a monthly basis, you may have noticed that the consumption is significantly higher than advertised.
It can be a big source of frustration, given that fuel consumption is usually one of the single most important factors to look at when deciding on your next car.
Reading between the lines
To answer the question of why your fuel usage is higher than what the manufacturer claims, we first need to understand how carmakers come up with these figures in the first place, and what they actually mean.
Auto companies run their new models through hundreds of tests to assess everything from the electrics to performance and reliability, with the fuel consumption trials comprising two phases – the “urban” cycle and the “extra-urban” cycle, writes Australia’s Drive.
Urban testing is intended to simulate a city environment and examines how the vehicle performs at an average speed of 60km/h or lower with constant stop-starting and significant idle time, as you would expect with heavy traffic in a high-density area.
The extra-urban cycle (sometimes referred to as the rural cycle, depending on the automaker) runs the car at higher speeds of between 60km/h and 120km/h and is meant to give an estimate of its fuel spending on the highway.
In a nutshell, a car’s urban figure is meant to represent its inefficient consumption, while its rural figure theoretically shows how it performs under ideal circumstances.
However, companies tend to advertise what is known as the “combined fuel cycle” figure.
The combined value is calculated as an average between the urban and rural numbers, with the urban figure being weighted more than its counterpart (usually around 67%) since most consumers are expected to spend the majority of their time commuting rather than driving on uninterrupted stretches of open roads.
It’s also important to note that the urban and extra-urban cycles still represent the car under testing conditions, meaning they are likely to be optimistic projections and that, in a real-world setting, it may still be possible to get a worse average than even the urban consumption.
Certain carmakers may provide the full breakdown of their car’s fuel consumption in the brochure, but this can be rather consistent.
VW South Africa, for example, lists the urban, rural, and combined usage numbers in its Polo Vivo brochure, but has not done the same for the Polo’s brochure.
Using the Polo Vivo as an illustration, we can see a breakdown of the three different cycles:
| Engine | Extra-urban cycle | Urban cycle | Combined cycle |
|---|---|---|---|
| 1.4-litre petrol | 4.5l/100km | 7.6l/100km | 5.7l/100km |
| 1.6-litre petrol | 4.9l/100km | 8.2l/100km | 6.1l/100km |
| 1.0-litre turbo-petrol | 4.0l/100km | 5.5l/100km | 4.8l/100km |
The combined figure is the one that you will most commonly see being used to advertise the vehicle in question.
It’s therefore worth asking how you use your car, because if 90% of its time is spent in rush hour traffic getting to and from work or dropping the kids off at school, its consumption figure is likely to be much closer to its urban figure than its marketed combined one.
Keyword: Why you car’s petrol consumption is never as good as advertised