True MPG: How realistic are official fuel economy figures?

Official fuel economy tests have been under scrutiny ever since they were first published, with drivers regularly noting how hard it was to achieve them in the real world, where traffic, temperature, wind conditions and more influence results.

Indeed, our testing showed that the average difference between the official figures and what was actually acheivable was an incredible 23.5%, with the biggest ever gap recorded being 41%. 

With this in mind, it was welcome news when the authorities replaced the old NEDC test with a new, more stringent WLTP test. But how accurate is this?

Below we have highlighted the five cars that actually beat their official MPG figures, plus the five that were furthest away.

1. The car that beat its official fuel economy by the biggest margin: Ford Ranger 2.0 diesel

Official MPG 30.7mpg | True MPG average 36.5mpg | Town 25.4mpg | Motorway 35.6mpg | Rural 48.7mpg

These True MPG figures were achieved in the range-topping 210bhp 2.0 Ecoblue 213, proving that big, heavy pick-up trucks can benefit from powerful engines that can be driven low in the rev range. Furthermore, the Ranger benefits from a 10-speed automatic gearbox, which can seamlessly slot into the most efficient cog at any time. It's not the most refined diesel engine, though (if you're used to driving a relatively hushed SUV you'll notice the difference).

Read our review of the Ford Ranger

Read on to find out how we conduct our True MPG tests, to see more of our True MPG test stars, and discover which five cars have fallen the furthest short of their official fuel economy results.

True MPG: how we test a car

To ensure they are repeatable and comparable, the What Car? True MPG test is undertaken on a rolling road set in laboratory conditions. This ensures that variables, such as traffic or inclement weather, don't bias our results. The route the car is 'driven' on is a real-world one, taking in a variety of speeds.

Prior to every True MPG test, the car's tyre pressures are checked and weight recorded. If the car has climate control, it is set to 21C. If not, we set it to the midpoint, with the fan speed on its lowest moving setting. All electrical equipment, from headlights to heated seats or the radio, are switched off.

The only additional piece of kit attached to the car is an exhaust connector, which channels emissions and allows them to be recorded every second. The True MPG scores we then report are based on an average of those results.

Other cars which beat their official MPG figures

2. Isuzu D-Max 1.9 diesel

Official MPG 30.7mpg | True MPG average 35.2mpg | Town 28.2mpg | Motorway 33.8mpg | Rural 42.8mpg

It's just as well the D-Max's 1.9-litre diesel engine is so efficient in the real world, because it's the only one that this rough-and-tumble pick-up truck is sold with. It's economy owes much to its ability to pull the D-Max along at low revs. Indeed, at higher revs it quickly runs out of puff. In our testing, the engine was linked to a decent six-speed automatic gearbox, its only fault being a reluctance to kick down, but a manual model is also available.

Read our review of the Isuzu D-Max

3. Honda CR-V Hybrid 2.0 i-MMD petrol

Official MPG 42.2mpg | True MPG average 47.4mpg | Town 47.6mpg | Motorway 38.9mpg | Rural 65.8mpg

The CR-V is our best-performing petrol model, with its slick hybrid system and a smooth automatic gearbox. Better still, it achieved a What Car? True MPG figure more than 12% better than the official figures would suggest, nudging it up to a highly credible 47.6mpg average. The two-wheel-drive model is the most efficient, although the penalty for choosing four-wheel drive is slight. The only disappointment is the CR-V's 750kg towing limit, which is lower than quite a few rivals.

Read our review of the Honda CR-V or see new Honda CR-V deals

4. Volkswagen Up 1.0 S/S 60PS petrol

Official MPG 50.7mpg | True MPG average 56.0mpg | Town 44.3mpg | Motorway 51.9mpg | Rural 72.2mpg

Downsized 1.0-litre engines have a reputation for returning great official fuel economy but disappointing real-world figures. The little Up turns that argument on its head though, and proves that this is the right-sized car for a small engine. This result was achieved with the 59bhp unit, which is no longer on sale new but is reasonably common on the used market. The 64bhp unit sold with new cars today is more powerful and not quite as efficient, but is still very recommendable.

Read our review of the VW Up or see new VW Up deals

5. Mazda MX-5 2.0 petrol

Official MPG 40.9mpg | True MPG average 45.1mpg | Town 33.2mpg | Motorway 44.4mpg | Rural 56.5mpg

We've tested the more powerful engine option available in the MX-5 here: the 181bhp 2.0-litre unit, as opposed to the cheaper if slower 130bhp 1.5-litre that is our pick of the range for most buyers. The revelation is that it can deliver the best of both worlds – incredible economy when you are out cruising thanks to its reserves of power, as well as a fair whack of oomph for some extra fun if you want to work it hard and push the revs up (and are prepared to watch as your fuel economy plummets).

Read our review of the Mazda MX-5 or see new Mazda MX-5 deals

And in reverse order, our poorest performers relative to their official MPG result:

5. Peugeot 308 1.5 diesel

Official MPG 65.4mpg | True MPG average 50.4mpg | Town 44.1mpg | Motorway 45.4mpg | Rural 62.7mpg

The 1.5-litre diesel engine we tested here is badged 1.5 BlueHDI 130 and linked to an eight-speed automatic gearbox. You'd expect that to be an economical combination, but while a real-world figure of more than 50mpg is decent, it is almost 23% short of the official calculation. Part of the problem is likely that the engine pulls only reasonably from low revs, prompting a driver to build up engine speed – at the cost of efficiency – to gather momentum.

Read our review of the Peugeot 308 see new Peugeot 308 deals

4. Ford Focus 1.0 petrol

Official MPG 65.4mpg | True MPG average 50.4mpg | Town 44.1mpg | Motorway 45.4mpg | Rural 62.7mpg

We recorded our figures with the most powerful 1.0-litre petrol in the Focus range, the 53bhp 1.0 Ecoboost Hybrid 155. While it's keener than the lower powered and cheaper 1.0-litre engines in the range outside of town, the extra power isn't transformative on the car's performance and, as revealed in our tests, isn't as economical as the official figures suggest. The engine was mated to a six-speed manual gearbox in our test.

Read our review of the Ford Focus or see new Ford Focus deals

3. Ford Puma ST 1.5 petrol

Official MPG 47.9mpg | True MPG average 35.4mpg | Town 27.0mpg | Motorway 34.0mpg | Rural 44.6mpg

Another Ford in the bottom five, and this time it's the sports-orientated Ford Puma ST that's in the spotlight for all the wrong reasons. The three-cylinder, 1.5-litre engine produces an impressive 197bhp of power and punchy 236lb ft of torque. That's enough performance to go from 0-62mph in an eye-catching 6.7sec. Our results show clearly, however, that all that pace comes at a price when it comes to real-world fuel economy.

Read our review of the Ford Puma ST or see new Ford Puma ST deals

2. BMW 4 Series 420d 2.0 diesel

Official MPG 57.6mpg | True MPG average 42.4mpg | Town 28.4mpg | Motorway 40.9mpg | Rural 60.0mpg

Cars powered by BMW's 2.0-litre diesel engine have long had a legendary reputation for providing a brilliant blend of performance and economy; not so here, in the 4 Series. The version tested here has 187bhp and plenty of pace – 0-62mph takes 7.1sec and B-road blasts plenty of fun – but not even its slick eight-speed automatic gearbox can save it from missing its official fuel economy figures by 26.4% in our True MPG tests.

Read our review of the BMW 4 Series or see new BMW 4 Series deals

1. Volkswagen Caddy Life (SWB 5-seat) 2.0 diesel 

Official MPG 55.4mpg | True MPG average 36.8mpg | Town 37.4mpg | Motorway 39.5mpg | Rural 33.9mpg

Take one look at the Volkswagen Caddy Life and you'll quickly understand that it is built for practicality above all else – it's boxy shape and convenience-orientated interior make it a great way to transport lots of people in comfort. But don't get into it expecting to match its official fuel economy figures. Our testing suggests a shortfall of 33.6% from that figure, and a relatively lowly 36.8mpg average overall.

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