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Debunking ADR Fuel Consumption Figures

We’ve all seen the fuel consumption stickers attached to every new car’s windscreen. But how are the figures calculated, and what do they mean in the real-world?

As society shifts towards a green energy future, it was inevitable that the automotive world would be swept up by the ever-building wave of environmental sustainability.

Manufacturers were once boastful of their power and torque figures, with fuel consumption relegated to the fine print- if you could find a reference to it at all.fuel-consumption

It was perhaps the energy crisis of the early 1970s which first gave pause for them to consider just how much fossil fuel their products were burning as they supplied mass transportation to the world. Since that time, mechanical carburettors have been surpassed by electronically-controlled fuel injection, a far more efficient and accurate method of supplying fuel to the engine. This process has been refined further, with today’s ‘direct injection’ petrol motors providing excellent engine response and power while also being frugal with fuel. Additionally, diesel engines have found wide-spread acceptance across the globe thanks to their headline fuel consumption figures (though their pollutant levels are another matter).

When shopping for a new vehicle today, the government has ensured that Australians have a set of combined fuel consumption figures which allow us to directly compare rival models. Set under Australian Design Rule 81/02, manufacturers have to provide a windscreen sticker on all new cars which shows ‘urban’, ‘extra-urban’ and ‘combined’ fuel consumption in litres per 100 kilometres.

How are these figures arrived at?

Using a chassis dynamometer in a workshop, a sample vehicle is strapped on to the machine’s rollers and taken for a stationery spin. Each car uses either pump-grade diesel fuel or 95-octane unleaded fuel to ensure there is no fuel advantage. It is then run over 20 minutes, simulating the stop-start conditions of an urban drive, followed with a sustained run up to freeway speeds. The figures garnered are then merged to provide the headline ‘combined fuel use’ figure.

Although these tests are thorough- they use fans to simulate air-flow and the rollers to generate inertia- it is nevertheless very difficult to paint a truly accurate picture of that vehicle’s performance on the road; the external variables are too great.
Think of everyone you’ve ever sat next to as they drove. They all have their own driving habits, and that affects fuel use. Other variables, such as the road surface, gradients, altitude, temperature, fuel quality…the list goes on.

In practice it is our experience that the simulated figures are very difficult to emulate in real-world conditions, particularly with modern smaller-capacity turbocharged cars (not to mention the traditional large-capacity V8s) when you want to use the available performance- which is the point of buying such a car in the first place.

In essence, the ADR combined fuel use offers a valid point of initial reference, but when shopping for a new car should be used as a guide only.

5 comments

  1. jeff Lacey says:

    Have not had trouble getting ADR figures out of our cars, but only after they were run in. Have had 6 new cars in the family last 12 years 3 Subarus, two Fords and one VW. They all imporoved fuel consumption by between 1 and over 2 litres per 100k after 15000 to 20000k. I laugh when motor writers winge thay they cannot achieve ADR figures, it is because they are driving new tight engines and generally not driving like Joe Public.

    February 25th, 2013 at 12:33 pm

  2. Paul says:

    Australian Design Rule 81/02 for fuel consumption reporting, is about as dodgy as the rubbery Finance figures our Federal Govt puts out…..great figures, but lack substance and accuracy! With such modern and advanced computers, engineers, mathmeticians, and technology, the best we can do is a chassis dynamometer in a workshop. Take a least 20% of the claimed figures, and you have a better comparsion to choose your cars and the actual economy of your new car. Diesel figures tend to be more accurate over unleaded. Here is a thought…a 12 week logbook kept by an every day owner/driver for three driving conditions – city, country, and work-vehicle driving. Works for me, but probably not for certain Manufacturer’s .

    February 25th, 2013 at 1:47 pm

  3. Ken Frost says:

    Our best in our 2012 BMW X3 30d was after the had done 36’000 km, we filled the tank after driving from Canberra to Cobram VIC, 460 km average consumption 6.48 litres per 100km. Driving at 110 kph plus. Would need to stay down to 100kph to match the windscreen consumption. Noticeably better consumption now some k,s on it.

    February 25th, 2013 at 7:21 pm

  4. Around says:

    Actually the last sentence should read that the ADR information presents fuel consumption figures you are unlikely to ever achieve and will never ever better, no matter how hard you try.

    February 25th, 2013 at 7:35 pm

  5. Ian says:

    Have just bought a Hyundai i30 SLX 1.6 Diesel claimed on screen sticker 4.5 -5 Lts 100 Km’s When picked up from dealers Showed 11.1Ltrs per 100kms.Salesman said to us would get best part of 1000Kms from 53 Ltr tank when filled up we had achieved 484 Kms on 46 Ltrs no where near that claimed on windsceen sticker. Phoned service dept regards the consumption and was told we needed to drive the car 15000 Kms before they would look at checking fuel consumption. After filling & resetting meters consumtion which had dropped to 9.4 prior to refill our next drive back to the salesman came down to 7.4ltrs to 100 Kms. left with salesman to deliver to Service Dept who claimed to download updated software to the computer. Picked up car from service where it showed 9.7Lts per 100 Kms at distance now now travelled after about 76 Lts.put in vehicleless than 900 Kms. I will now wait for next refill & zero the dash metres to see what the result will be. I am to believe the metres or computer metres on the dash have to be zeroed at each fill which I already assumed had to be done on the last fill and this is when the shown consumption dropped to 7.4lts Per 100kms but distance to next fill showed less than 600 Kms. We will see. I am a mechanic by trade & the service & Salesman question was whether we were driving in (Auto) 1st gear. When I dropped the car to the salesman He ask me to show him which position we put the auto & I put it in D position.

    March 2nd, 2013 at 9:50 pm