/ Motoring

Car fuel economy claims are miles from the truth

Car wheel

We already know that ‘official’ car mpg figures are rarely possible in the real world – our tests show that. But choosing larger alloy wheels could see your fuel bills increase even more.

As part of the Which? Car team, I get more emails about fuel economy than anything else. They inevitably start by mentioning the official EU test figure, as quoted by the car manufacturer, then explaining how their car can’t get within 20 miles per gallon (mpg) of that number.

That’s why we think our mpg tests are more realistic. They include cold starts and motorway driving – both absent from the official EU cycle.

However, official figures could be even further from the truth – depending on the wheel-size of the car you buy. Opt for big alloys (as many style-conscious buyers do) and your fuel economy could drop significantly.

Different wheels, different mpg

At the moment, Toyota and its sister-brand Lexus are the only companies to quote separate economy and CO2 emissions figures depending on wheel size.

For example, buy a Lexus IS 300h in entry-level SE spec and it comes with 16-inch wheels. Quoted economy is 65.7mpg with CO2 emissions of 99g/km (grams of carbon dioxide per kilometre driven). However, stretch your budget to the Luxury model and you’ll also need to stretch your fuel allowance; its 17-inch alloys reduce efficiency to 64.2mpg (103g/km CO2).

At the top of the Lexus IS range is the F Sport version. This has exactly the same engine and electric motor, but with 18-inch rims its claimed economy is 60.1mpg (109g/km CO2). That’s an increase of nearly 10% over the SE model – almost entirely because of those larger wheels and tyres.

To put that in perspective, a driver covering 12,000 miles a year would spend £107 more on fuel for the F Sport than the IS 300h SE. Plus, annual car tax (VED) costs £20 – rather than being free.

Same car, different wheels

Now let’s look at one of the IS’s rivals. The BMW 3 series is the UK’s bestselling large car, yet its maker quotes identical fuel economy and CO2 emissions for all models, whether with 17, 18 or 19-inch alloys.

I believe Toyota and Lexus deserve credit for being upfront about fuel economy figures. It’s time other car companies followed suit.

Can you match your car's mpg claims?

No (69%, 784 Votes)

Yes (18%, 205 Votes)

I don't know (13%, 153 Votes)

Total Voters: 1,150

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It is well known that EU fuel consumption figures do not represent real-life consumption, and are not intended to. They are precisely controlled tests to compare different cars on an equal basis, and presumably to provide a basis for emmission taxation.

The way to get real-life consumption is from drivers reported information – and particularly, I suppose, from fleet operators. Honest John at the Daily Telegraph publishes these. So do Which? and other motoring publications.

Even then, your own consumption will depend on how you drive and your journey pattern, so it would be impossible to give a consumption figure that would apply to all drivers – only a range would make any sense.


For emmission, read emission!
Dear Which? When can you introduce editing of posts please? Even if it involves deleting your offending post and resubmitting it.


Please don’t worry about typos Malcolm – if you are concerned report your comment and I’ll fix the typo. Thanks

Colin Samson says:
15 September 2013

Ha Ha! “Emmission” stuck out like a sore thumb to me too. I’m glad that I’m not alone in finding such errors to be irritating. The spell checker usually shows that a word is misspelled when these posts are being typed, as the word “Emmission is highlighted as I write this now; so there should be no excuse.

“TV’s” is another error showing up on Which? reviews. There should be NO apostrophe as the abbreviation is plural (more than one television); it should spell as “TVs” or arguably “TVs.” with a full stop to show it is an abbreviation of “Televisions”. Unfortunately the daily press is usually littered with spelling & grammatical errors so it is no wonder that standards elsewhere are plummeting.


Hi Colin, Malcolm’s referring to the error in his own comment (sorry Malcolm!) However, if you ever spot a typo in something we’ve written please do tell us. Sometimes mistakes slip through, but we do like our copy to be error free. TV’s is an annoying one! Now, back on the topic of car mpg claims…


We could do with an easier way of reporting errors in the introductions to topics than using a Web-based form and putting in name, email address, subject and message.

Incidentally, the energy campaign logo has KWh rather than kWh. I’ve seen kW/h in an earlier Conversation. 🙁



petty Dare I say


But accurate. We should preserve correct English – it has a purpose. Two things (well two of the many things actually) that irritate me are the misuse of apostrophes and beginning spoken sentences with “so”. Sorry to deviate from the topic.