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.
Was this article useful? Please take a couple of seconds to rate it below, and share it with your friends!
Leave a Reply
You must be logged in to post a comment.