With two bank holidays in May, we asked our True MPG team to investigate the effect of fitting a roof box to your car.
What did we learn from it? One thing’s for sure, you’ll definitely want to remove the roof box between the two long weekends. Driving around with a roof box on could cost you dearly.
The research showed that fitting a roof box could mean your car’s fuel efficiency will be reduced by just more than a third from the figures quoted by the manufacturer.
The What Car? True MPG team tested two popular family cars on the road – the Dacia Logan andNissan Qashqai – with and without roof boxes.
Without roof boxes, the two vehicles have already been proven by the True MPG team to perform worse than their officially quoted MPG figures, with the Logan achieving 27% less than its official figure and the Qashqai getting to within 21% of its Government-sanctioned MPG rating.
Adding 50kg of weight to 430-litre roof boxes, however, meant the cars performed even worse, achieving 35% and 31% under their official MPG figures respectively.
What Car? editor, Jim Holder, said: “The vast majority of cars are unable to match the official MPG figures that manufacturers quote even before the addition of a roof box. Adding the box increases the overall weight of the car and increases aerodynamic drag, so it stands to reason that your fuel efficiency will be harmed.”
“Taking a break in the UK might be considered a sensible thing to do in order to save some money but you’re effectively paying for it in other, less obvious ways.”
With roof boxes fitted, the Dacia achieved 48.5mpg and the Qashqai 32.1mpg – well beneath their official figures of 74.3mpg and 47.1mpg.
Since What Car? took action and launched True MPG with official fuel partner Tesco in 2012, more than 600 cars have been assessed in real-world conditions, using cutting-edge test equipment, achieving economy figures that are an average of 20% lower than the Government figures, calculated only via laboratory testing.
What Car? True MPG data is scientifically calculated by experienced engineers, who drive test vehicles over a variety of real roads, including motorway, A- and B-roads and in towns and villages.
Want to find out what you can really expect to achieve on UK roads? Visit whatcar.com/truempgto see the full range of cars we’ve tested. We add new models to our True MPG database every week.
Read more about Real-world MPG: The true cost of attaching a roof box on The Best Car Roof Boxes Reviewed.
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