Fuel Economy: Real-World vs. Official Figures
One of the biggest complaints drivers have about their cars is poor fuel economy, or more specifically that the car uses a lot more fuel than the manufacturer’s figures suggest. The Car Expert is here to explain why.
Every new car in the UK has three official fuel consumption (fuel economy) ratings – Urban, Extra-Urban and Combined. Urban is supposed to represent city driving, Extra-Urban represents country roads and motorways, and Combined represents an overall figure. But most motorists will tell you that they are unable to get anywhere near their car’s official fuel economy figures, and it usually drives them mad.
How is fuel economy calculated?
The first thing to understand that a car’s “official” fuel economy figures are not measured by the manufacturer. Instead, they are calculated by the government to a uniform EU standard, using a standardised and carefully controlled laboratory testing program – known as the New European Driving Cycle. This means that every car on sale in Europe can be compared using the same tests, so you can compare the relative fuel economy of Car A with Car B. However, the system does have its drawbacks.
One of the problems is that the test routines are relatively simple and do not tax the car greatly, meaning the results will be very favourable. There are also no complications like hills, headwinds, traffic, different drivers with different driving styles, weather variables, luggage, under-inflated tyres, and other factors which will affect fuel economy. The results will always be a best-case scenario.
The other problem is that car manufacturers are very good at designing their cars to excel at relatively straightforward government tests like fuel consumption and crash testing. Modern on-board computers control every aspect of how your car performs, and those computers are programmed to do well in the exact conditions used by the fuel economy tests, even if they are not representative of the car’s normal operating environment. Sneaky, huh?
The net result is that the official fuel economy figures will almost certainly be considerably better than what you can expect to achieve in the real world (unless you do all your driving downhill with a tailwind). So why are the tests not just made tougher? Well, mainly because that would mean that you wouldn’t be able to compare a car tested under the new method with a car tested under the old method, and re-testing every car that has been on the market since 1999 (when the current test was devised) is not economically feasible. There is also not a lot of interest from the manufacturers, as tougher tests would make their new cars look less economical than their old cars, even if this is not really true.
Various other people or bodies have had a crack at providing “more realistic” fuel economy figures for cars, the latest of which is WhatCar? magazine’s new ‘True MPG’ program. Although the fuel economy numbers they provide may be more ‘realistic’ (ie – thirstier) than the official tests by driving on ‘real roads’ and carrying more weight, they cannot match the consistency of laboratory testing and introduce all-new margins of error when estimating what you can expect a car’s fuel economy to be for your circumstances.
So how do I know what sort of fuel economy I can expect?
From a buyer’s perspective, the best way to look at any fuel economy claims is to view them simply as a guide to a car’s relative fuel economy rather than its absolute fuel economy. If your current car is officially rated at 30mpg but you only achieve 18mpg in your own driving, then you can expect a reasonably similar ratio when you’re looking at a new car which is officially rated at 60mpg (so, expect to get about 36mpg).
The Car Expert’s unique Driver Analysis helps clients understand fuel economy, how their driving affects how much fuel they use, and what sort of fuel consumption they can expect to get when buying a new or used car. If you are looking at buying a new or used car in the UK, The Car Expert can help you find the right car at the right price, potentially saving you thousands of pounds and lots of hassle.
Concerned about fuel economy? Here’s some more recommended reading:
Wondering about the merits of running a diesel car for use in city driving? Read The Car Expert‘s article about what you need to consider when using a diesel car for urban driving.
Should you pay extra for premium fuel? The Car Expert looks at whether premium diesel and petrol are worth the money.
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@David Dixon – I feel your pain, brother. I had a BMW diesel which claimed to get about 58mpg but I never got any better than about 40. About time the whole system was overhauled to make it more relevant IMHO.
Unfortunately, David, stories like yours are relatively common. Not just with Audi or any particular brand, but across the board. This is one of the reasons that the EU is considering a change to the official government fuel consumption test regimen, so that the official figures become more representative of a majority of real-world drivers.
Of course, fuel economy can be affected by other factors such as driving style, under-inflated tyres, carrying extra weight in the car (a surprising number of people haul all sorts of things around in their car which add up to a significant amount of weight), roof racks, wider tyres (often found in sports models), and so on. ‘Premium’ diesel fuel may give you slightly better economy than ‘regular’ diesel (although it is more expensive so may not actually save you any money).
Finally, diesel engines can take 10,000 miles or more to truly run in, so it is possible that you will still see some slight improvement on your current figures, although it wouldn’t be a lot.
Some, all or none of that may help you in your current situation, but keep pestering Audi if you feel there is a problem with the car. Also make sure you keep track of your fuel spending and mileage, and keep track of your contact with Audi.
stuart
I have a real problem with my fuel economy, purchased a brand new Audi A4 Avant 2.0 TDi Quattro Dynamik in an 2012, I’ve so far covered just under 8000 miles, and on average my fuel consumption is only 35.2 MPG what was tracked over 7300 miles!
To me that is ridiculous values below what’s actually produced on the datasheets when you buy a car. I expected it to be lower, but not THAT much lower!
I contacted Audi Customer Services who said there’s a 33% tolereance level in place, which means on a combined cycle they can quote 53.4MPG but in read life it can be as low as 35.7MPG, but mines even below that, but they are not willing to look into it as a problem. I visited my local Audi dealership who done a fuel consumption test and it came out to 50.4MPG. They used the Audi DIS in order to collect this information so not exactly an accurate reading, mine average was worked out of fuel filling and mileage covered. It took me 3 attempts to get that reading on the DIS which meant driving the car without engaging the turbo, and coasting down a large hill on the way back to the Audi center! Hardly a worth while test!
If I had known at time of purchase that it was going to be this bad, I’d have probably purchased the petrol as most petrol owners I’ve spoke to get around the 32-34MPG mark, and petrol is cheaper than diesel!
I find myself in the position where Audi Customer services don’t really want to know, and have fobbed me off to my dealership, the dealership has no cars they can offer me without putting more large sums of money into it. And a car exchange offer means I’d need to payout £3000 to get another car … which would be another 2.0 TDi !
Audi’s 2.0 TDI Fuel consumption is a joke, and according to multiple forums I’m not the only one experiencing this! I think this large gap needs to be brought to the attention of consumers, and something real world needs to be offered at time of purchase so your better informed to make a decision rather than just getting quote untrue figures!
Agree with what you say about new cars looking better on paper but not doing any better in the real world. I have had Passats as company cars for about 8 years, doing about 50,000 miles a year and changing cars every two years. Every new one is supposed to get much better fuel economy figures than the old one, but in reality they’re never really any better. I’m still getting 40mpg, which is pretty much what I’ve always been getting.
Hi Fred, great to hear from you (Fred bought a Volkswagen Passat from me when I worked at a VW dealer in Australia). I believe that the Australian tests are very similar to the EU tests, although they are probably more suitable for Australian conditions due to the (usually) better flow of traffic and ridiculously low open road speed limits. Also, Volkswagens from the mid-2000s seemed to have official fuel economy figures which correlated quite closely with real-world driving. These days VW seems to have joined the rest of the industry in optimising their engine management systems for the official tests while real-world figures are not really much different. Best wishes, stuart.
Hi Stuart
From a ‘downunder’ old VW Passat driver. Agree with your comments. My experience with fuel figures for my car is very close to what is specified. The combined figure is 6.7litres/100kms with my urban around 7.2 and extra urban at 5.7 with at least 3 people and luggage.
Do the tests for ‘down under’ vehicles use the same criteria as the EU?
When will the UK adopt a uniform measurement system MPG what is that??? (dark ages or from the USA)
Hi Kate. Will add it to the list of future blog topics. Hope you’re still loving the Mini! stuart
Very interesting stuff – I spotted a comment you made regarding modern usage of on-board computers in cars – having never thought about computers in that context, beyond Formula 1 or supercar scenarios – I’d be interested to hear how that technology works in an every day car, and how it will develop further.