Will A Roof Box Increase My Fuel Consumption?

Introduction

Unfortunately adding a roof cargo box to your vehicle will have a detrimental effect on your fuel economy. There are a number of ways to reduce the effect, however. Let’s take a look at why adding a cargo box makes you use more gas and how you can try to reduce the effect.

Aerodynamics

Adding a storage box on top of your car will affect the aerodynamics of the vehicle. Depending on the size and shape of the carrier you are going to increase the level of air resistance which means an increase in the amount of gasoline used.

The size and shape of some rooftop boxes are likely to mean much greater wind resistance and therefore more aerodynamic drag causing an increase in fuel consumption.

Weight

Even an empty carrier will add to the total weight of your vehicle. Some roof boxes could be as much as 60lbs in weight, more when you add on the weight of any bars or roof rack. While it may not be a massive percentage increase in the total weight of your vehicle it will mean using more gas on your journey.

How To Improve Your Fuel Economy

The best way to improve your gas mileage would be to remove the box unless you really need it! Are you carrying loads of unnecessary items in your trunk? If so, then remove them and put the contents of your roof box in the trunk instead so you can take the roof box off!

If you really need the box then try to make sure you purchase the most aerodynamic design possible so as to minimize the amount of additional drag that it causes. 

In tests, ConsumerReports found that even an empty roof rack caused between 1% and 11% additional fuel consumption. Adding the box caused that to increase to between 13% and a whopping 19%!

In an article by Berkeley Lab they showed that 0.8 percent of gas used in the USA in 2015 was due to additional drag caused by roof racks. That’s the equivalent of 100 million gallons of gasoline!

You should also try to get the most aerodynamic and lightweight roof rack or roof bars since this will minimize wind resistance and should also help reduce wind noise.

Most vehicles will achieve optimum fuel economy in the region of 50 to 60 mph. Even with the reduced aerodynamics and additional weight, your vehicle is still going to be most efficient at those sorts of speeds. Sticking to the speed limits or even slightly below them will see you improve your fuel economy with or without a roof carrier.

In addition, it’s likely that your vehicle manufacturer will advise different tire pressures when you are fully loaded or traveling at highway speeds. Make sure that you have adjusted your tire pressures to match the manufacturer’s specifications. This is an often-overlooked reason for reduced miles per gallon figures. 

The price of gasoline will probably affect your behavior somewhat. The price of fuel in Western Europe tends to be significantly higher than in North America for example, although trips tend to be shorter – partly due to the cost of a gallon of gas.

Exactly the same will hold true for an electric vehicle. Adding extra weight has an impact on how much battery power you consume because it has to work that bit harder. 

Driving style also has an effect on your gas mileage. Try to improve your ability to read the road ahead so that you can accelerate and decelerate smoothly rather than hitting the gas or the brakes hard!

The US Department of Energy suggests taking these measures to improve your fuel economy.

A lower MPG figure is one of the biggest downsides of fitting a roof storage box!

Will A Roof Box Increase My Fuel Consumption: Conclusion

Adding roof storage to your vehicle will have an impact on fuel economy. The size, shape and weight along with the cargo you carry will determine how much of an impact. Following manufacturers instructions will help plus the use of common sense and a more economical driving style.

So to recap:

1. Buy the most aerodynamic model possible

2. Only fit it when really necessary

3. Adjust your driving style to be more fuel efficient

Frequently Asked Questions [FAQ]