What do fuel consumption labels really tell you?

21 March, 2022   By: Ryan Suckling

Just like the energy rating labels found on white goods, these stickers, found on the windscreen of new cars, are mandated by the Australian Government for all new light vehicles with a mass of up to 3.5 tonnes.

The information on the label offers a laboratory-tested estimate of both fuel consumption in litres per 100 kilometres, as well as carbon dioxide emissions in grams for every kilometre driven.

However, as the tests for these estimates are done in laboratory conditions, there have been concerns raised about how accurate they are compared to the fuel consumption achieved in real-world driving conditions.

While there are typically differences between the fuel consumption numbers returned in real-world driving and those of a tightly controlled laboratory test, the key advantage of the laboratory test is the ability to compare results with more precision across different vehicles.

The downside is that these aren’t always representative of your actual fuel consumption. Fuel labels can still be useful – they just need some interpretation when it comes to understanding what those numbers mean when you’re on the road.

RELATED: The cheapest cars to own and run »
RELATED: Petrol versus diesel cars - which should you choose? »

Fuel consumption categories

The fuel consumption figures on the labels are broken down into three categories: Urban, Extra Urban and Combined. These figures represent estimates of fuel use in varied driving conditions, such as stop-start city driving and higher speed, long-distance driving, such as on main roads and highways.

Urban and Extra Urban

The first phase the fuel consumption test run on a car is the Urban cycle. This simulates lower-speed urban driving conditions, where the car is frequently stopping and idling. Here, the average speed is 19km/h and records a much higher level of fuel consumption.

The second phase simulates driving in less congested conditions. The Extra Urban cycle runs on an average speed of 63km/h to replicate highway driving where motorists experience more constant speeds for longer periods of time.

Combined

The combined figure, seen at the top of the fuel consumption label, is intended to provide a more realistic picture of real-world fuel consumption. Considering both stop/start traffic as well as steadier highway driving, the combined figure is used as a more accurate reflection of varied driving conditions.

Electric car energy consumption

A couple of years after the labels were introduced, the mandate was extended to electric cars to include a label which shows an estimate of energy consumption. The labels can be seen on pure electric cars and plug-in hybrids, showing the car’s energy use in watt hours for every kilometre travelled.

The label also gives an estimate of the electric car’s range in kilometres when fully charged.

RELATED: How much does it cost to charge an electric car? »

How is the fuel consumption of cars tested?

All new cars sold in Australia must undergo the fuel consumption test. So how exactly is that done in a lab?

The car is positioned on a rolling powertrain, or standard dynamometer, and runs through a series of speed changes during each of the two testing phases. During the first phase, the Urban Cycle, the car undergoes periods of acceleration, deceleration and idling. The equivalent of four kilometres is travelled and the maximum speed is 50km/h.

The car then enters the second phase, the Extra Urban cycle, where it is run at constant speeds over a total of seven kilometres. The highest speed reached during the testing is 120km/h then towards the end of the cycle, the car undergoes some idling as well as acceleration and deceleration.

The rules specify that fuel consumption testing for vehicles sold in Australia be conducted under conditions outlined in an older type of test cycle, called the New European Drive Cycle.

However, vehicle manufacturers are increasingly also providing their consumption numbers according to an updated test standard known as the Worldwide Harmonized Light Vehicles Test Procedure (WLTP). The WLTP provides values that are much closer to reality than the NDEC (which was developed in the early 1990s).

Controversy and testing conditions

The suitability of current fuel consumption testing relates to how different the controlled laboratory conditions are from how most cars are driven in the real world.

Some manufacturers have even been caught out for misrepresenting the fuel consumption of their vehicles, even though they were simply following the regulation test requirements.

In 2019, Mitsubishi was ordered by the Victorian Civil and Administrative Tribunal to refund the purchase price of a 2016 Triton after the owner was able to prove that the vehicle’s estimated fuel consumption was “misleading and deceptive”. The owner found that the fuel consumption of his previous 2008 model was lower than the newer Triton, despite claiming otherwise on the label.

Mitsubishi Australia now also faces a class action based on more than 70,000 Triton utes sold between 2016 and 2018. The manufacturer is defending the claim, saying its laboratory tests are conducted as required by current government regulations.

The laboratory tests are designed primarily to be a tool for comparing the fuel consumption of different models when they are subjected to exactly the same test, and while they were not intended to represent real-world driving conditions, consumers often make the assumption that they do.

In the time since the NDEC was originally developed, consumers have increasingly expected that these results do represent real-world driving conditions. At the same time, cars have increasingly become better at completing the test.

Real-world driving conditions are also heavily influenced by how much weight the vehicle is carrying or if it’s towing a load. The test has also proved to be problematic when conducted on plug-in hybrids (PHEVs), where fuel consumption entirely depends on how much charge the battery has.

The testing model used in the USA is considered by some as a more effective way to conduct fuel consumption testing and one which Australia should consider adopting. Carried out by the Environmental Protection Agency, their process for determining fuel consumption combines both laboratory testing and real-world driving. The issue is that this testing regime is more expensive to run.

So while laboratory testing isn’t a true representation of real-world driving, the testing is nevertheless carried out in strictly controlled conditions in accredited laboratories and does allow consumers to easily compare results across vehicles.

However, the unfortunate side of using of the NEDC test procedure is that those results will, for most vehicles, be approximately 20-30 per cent lower than motorists can expect to get in real-world driving.