Why you can’t match your car’s claimed fuel economy
THE accuracy of the Australian Standard test used to measure new car fuel consumption and emissions has always been highly questionable. It looks as if it's going to stay that way for some time, as the Australian Government has no plans to adopt a new, much tougher and more accurate test now in force in Europe.
The new Worldwide Harmonised Light Vehicle Test Procedure - thankfully abbreviated to WLTP - is still done on a laboratory bench but the simulation aligns much more closely with real world driving conditions.
It produces more realistic consumption figures than the official Australian test, which is based on Australian Design Rule 81/02.
This in turn is modelled on the superseded New European Driving Cycle set-up, designed in the 1980s.
When the rubber meets the road, the real figures are almost always higher than Australian test results quoted by car makers and displayed on windscreen labels in local showrooms. In city driving some cars, SUVs and one-tonners can use up to 50 per cent more fuel than the official average.
That's hardly surprising when you compare the Australian and European test procedures.
The local test is done over 11km and 20 minutes, with just two minutes of simulated driving at 80km/h or faster.
Average speed overall is 34km/h, in the city cycle it's just 19km/h and the vehicle is stationary for 25 per cent of the entire test.
That's the main reason car makers fit automatic engine stop-start - it makes their fuel figures look a whole lot prettier than if the car was idling for a quarter of the test.
WLTP is a 23km simulation that takes 30 minutes, with longer, more frequent periods of strong acceleration and high speeds - the average speed is 46.5km/h and the car is stationary for 13 per cent of the time.
In the Dieselgate scandal, diesel cars on the road were found to be producing an average of five times more harmful nitrogen oxide emissions than the superseded test indicated.
WLTP includes an extra emissions check on the accuracy of a model's laboratory results, comprising on-road tests of the same car, fitted with instruments to measure consumption and emissions while in motion.
If there's a substantial variation, the car maker gets a "please explain". After 2023, no variation will be allowed.
In line with the more accurate testing, the CO2 emissions and fuel consumption figures on labels attached to new vehicle windscreens in European showrooms will increase by an estimated 10-20 per cent.
"A modern certification process should provide values that are as close to reality as possible, (so) you can compare various vehicle models," says Mercedes-Benz. "The NEDC process no longer meets this requirement."
The Australian government has no plans to replace the local test with WLTP. The manufacturers themselves recognise that NEDC is, according to BMW, "totally outdated".
In part this is due to the fact that our unleaded petrol is permitted to have a sulphur content as high as 150 parts per million. WLTP tests are done using fuel that complies with the much cleaner EU requirement of 10 ppm maximum.
Some European makers claim this will lead to new models being unavailable in Australia, either because their latest engines won't operate on our dirty petrol, or because they aren't willing to spend millions complying with the outdated standard for our small market.
"The sooner Australia harmonises with European fuel and testing standards, the better for Australian consumers," says VW Australia's Paul Pottinger. 'Unless a means is agreed upon to recognise WLTP results here, the choice of vehicles available to Australians will continue to diminish."
The Department of Infrastructure, Regional Development and Cities is responsible for emissions tests. Asked whether the European stand would be adopted in Australia, a spokesman said: "The department will continue to monitor international developments regarding WLTP and consider whether ADR81 should be reviewed."