Fuel Economy is your car’s fuel consumption in litres per 100 kilometres travelled (L/100km). The better fuel economy a car has, the more desirable it is for consumers. In Australia, some of the models with the best fuel economy include the Suzuki Swift, Skoda Fabia, and Citroen C4 Cactus.
Now, you might be thinking, “Can the fuel economy declared by the manufacturer be trusted?” or “Is fuel economy tested according to real-life driving conditions?”. Well, until recently, the answer to both questions was ‘No’.
For almost three decades, fuel economy was tested through the New European Driving Cycle (NEDC). It’s a fuel economy and emissions test standard based on theoretical driving. But automotive technology has since been upgraded and people have been driving with different road conditions for years, which made the NEDC outdated for quite some time. And because of this, car companies have been taking advantage of some loopholes to make the results more advantageous for their products.
Thankfully consumers began to question the NEDC results and in response, the United Nations and European, Japanese, and Indian regulators devised a new standard called the Worldwide Harmonised Light Vehicles Test Procedure (WLTP). It was implemented back in September 2017 and since then, cars brought to Australia have a fuel economy rating based on the WLTP standard.
How does WLTP work?
With WLTP fuel economy testing, vehicles are sorted into three classes.
- Class 1 vehicles are low-powered and have a power to weight ratio (PWR) of 22 or lower.
- Class 2 cars have PWR between 22 and 34.
- Vehicles with PWR above 34 belong in Class 3.
PWR is derived by dividing the car’s kilowatt output by the kerb mass (tonnes).
Modern, higher-powered cars belong in Class 3. They undergo four different tests that simulate real-world driving and in different speed conditions (low, medium, high, and extra high). The test cycle is 30-minutes long.
During the low-speed phase, the vehicle being tested will run up to 56.5km/h only, lasting for 589 seconds. It will accelerate and decelerate to various speeds and will stop five times or more at different durations. For the medium-speed phase, the duration is 433 seconds and the vehicle will only stop one time. The maximum speed for this phase is 76.6km/h.
On the third phase (high-speed), the vehicle will run at a maximum speed of 97.4km/h and for 455 seconds with a 31-second stop. As for the extra-high-speed phase, the vehicle will run 323 seconds and for up to 131.3km/h, with an 8-second stop at the start of the phase. All in all, the vehicle should cover 23.266 kilometres during a WLTP test.
Why is the WLTP better than the NEDC?
Below are the main improvements that WLTP brought to fuel economy testing over the NEDC:
- More variation in driving conditions, such as urban, suburban, main road, and motorway.
- Longer test distances.
- Higher maximum speeds.
- Stricter measurement conditions.
The new standard is better than NEDC because it is based on real-driving data, which will result in more realistic fuel economy ratings. WLTP also considers the vehicle’s internal parasitic losses due to the undriven axle’s rotational inertia, which is the front wheels axle for RWD and the rear wheels axle FWD cars. In WLTP, the fuel usage is multiplied by 3% in coast down tests to account for this rotational inertia. On the other hand, NEDC testings do not consider this.
More importantly, WLTP results are not easily manipulated compared to those of NEDC.
What is the relationship between fuel economy and emissions?
The fuel economy of a car has a direct correlation to its CO2 emissions. For example, a diesel car with 3.7L/100km will produce 95g of CO2 every kilometre. The same amount of CO2 emissions is produced by a petrol car with a fuel economy of 4L/100km.
With the new WLTP standard giving a more realistic fuel economy result, you’ll also be able to determine your car’s CO2 emissions and if it’s compliant with the new Euro 6c standard.
In April 2020, Australians will begin to see new cars with a fuel economy rating based on the WLTP. That means you can better rely on the figures included in car specs to be an accurate reflection of the car’s fuel economy.
If you plan on purchasing a new car, make sure it has been tested with the WLTP standard. This way, you’ll be able to accurately compute your actual fuel consumption and expenses to manage your finances. More importantly, you can trust that the new vehicle is emissions compliant. Another win!
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