In the wake of #dieselgate there are now reports that consumers are being ripped off with cars that use far more fuel than their claimed fuel consumption.

EVERY NEW VEHICLE on the Australian, and most other markets has to undergo a fuel efficiency test according to the Government standard ADR81/02 (Australian Design Rules).  This is a 20-minute, lab-based test in carefully controlled conditions – temperature (between 20 and 30 degrees C), air pressure, controlled fuel and the like.  The car is properly serviced, tyre pressures adjusted carefully, all lights and accessories are switched off, and the vehicle is unloaded.  The effect of the car’s weight and aerodynamic efficiency is considered as the vehicle is on a dynamometer, turning the driving wheels but not actually traveling.

There are two tests – the Urban and Extra Urban, taking around 13 and 6 minutes respectively.  The Urban averages a speed of 19km/h and frequent stop/start idle events.  The extra urban goes up to 63km/h and peaks at 120km/h.  Fuel consumption and emissions are measured across both cycles, and combined to make the Combined figure.  It is this figure that we, and most other media outlets quote.  Here is a graph, taken from the Green Vehicle Guide, that represents the tests.

ok, but am i being ripped off?

The problem, such that it is, seems to be that the real-world fuel consumption does not match the lab tests, and therefore some in the media are crying that consumers are being ripped off by car manufacturers.  We argue that is not the case.

Virtually every report you read about the official fuel consumption figures in the automotive media states that in many real-world conditions those figures will not be achieved, and indeed the Green Vehicle guide says: “..while the label enables you to compare vehicles with confidence, no single test can simulate all ‘real world’ driving conditions.  Actual onroad fuel consumption will depend on factors such as traffic conditions, vehicle condition and load, and how you drive.”   And if you read the figures from the manufacturers they state something similar.

There are many reasons why the real world doesn’t match the lab – typically cars carry several people, or have accessories fitted, tyre pressures are left to become low, accessories are fitted to the car which add weight and perhaps drag…so many reasons and of course the biggest one of all, inefficient driving style.  Often drivers find their fuel efficiency is 20-30% over the combined cycle.  And it’s no different with any other absolute figure that is subject to variables – go on a walking track and the guide might say you’ll need an hour for the trail, yet you may take half an hour or ninety minutes.  But you know the hour-long trail will taken longer than the thirty-minute trail.

The use of a set standard doesn’t mean people are being ripped off, because the conditions are the same for all vehicles so you can use it as a comparative measure.   After years of testing new cars, we can say that the the ADR81/02 tests do reflect real-world relative fuel consumption – that means the cars which score better on the lab tests will do best in the real world.  Will they meet their actual lab figure?  Probably not.  And that’s where improvement can be made – we do think the ADR81/02 test should be tougher, because it’s clearly not representing real-world conditions as well as it should be.  But that’s a matter for the government to address as they set the test, not the car companies.  It’s actually an international problem as the same test (or close to it) is used worldwide.

The car companies would only be ripping consumers off if they had special modes for lab testing, as we’ve seen in the current VW/Audi/Skoda #dieselgate scandal.

Can the lab figures ever be achieved?

Absolutely.  All you need to do is ensure the car is in good condition, lightly loaded and drive efficiently (techniques  will be posted here soon).  I once did a fuel consumption test in my Land Rover Defender 110 TD5 which had an ADR combined figure of 10.8L/100km.  I drove a bit more conservatively and managed 10.3 on a morning commute.  Then I dumped all my gear from the truck and really focused…managing to return 8.4L/100km – and that car had around 300kg of extra gear like a bullbar, winch, snorkel and mud tyres. 

So far, I’m yet to find any vehicle that can’t beat its own ADR81/02 consumption figure.  Even got our long-term i30 down to 4.7 when we did a few trips that involved a bit of freeway driving, slightly better than the 4.9 combined figure, and that wasn’t trying very hard either.

The problem we see is that the average driver is looking for a quick fix that requires no effort.  Sorry, but the only real way to be fuel-efficient is to drive efficiently which takes skill and sustained discipline.  We’ll run an article on how to do that shortly.

What’s a realistic guideline and are these lab figures any use?

If you want to see which of two or more vehicles are most efficient then you can use the ADR81/02 tests, and look at the relative percentage between the figures. 

But if you want an indication of real-world consumption…that’s much, much harder to predict.   Those who drive on flat rural roads at 100km/h will do a lot better than those in hilly urban areas who only drive for short periods with the engine often not warmed up.   If you carry a load, or passengers that’s extra too, and towing will throw the figures right out the window as will fitting of 4X4 accessories.

Still, as a general rule, if you want a real-world fuel consumption figure add around 20% to the ADR81/02 figure for around-town commuting.

Also note that the fuel consumption displays in cars are generally a bit optimistic, but they will be consistently out by the same amount so you can measure how well you’re doing.

Bottom line: the lab tests are a good comparative measure, but don’t reflect real-world conditions, the biggest improvement you can make to fuel consumption is your own driving style, and you’re not being ripped off.