The Effect of a Roof Rack on Gas Mileage - Vol.371
There's no doubt that a roof rack is a very useful thing to have - especially if you have a more compact vehicle. It allows you to store much more things that you would be able to fit into your car's trunk. Sure, it might not make your vehicle look beautiful, but one can't deny the usefulness. It's actually estimated that, by the year 2040, the use of roof racks in the United States will have increased by a whopping 200%!
Aside from ruining the aesthetics of your car, the use of a roof rack can have another, more serious consequence. Namely, the gas mileage of your vehicle can, and will be worse, when using a roof rack. It actually makes perfect sense when you think about it. An added roof rack means that your car has to deal with more wind resistance, and it will take it a lot more power to be able to go the same distance, which means increased fuel consumption. Just how much more fuel you're going to use with an added roof rack is hard to tell, as it depends on the type of the car and the size of the roof rack itself, but there's no denying the fact that more weight on the car, with larger size means worse gas mileage. This effect of air on objects is known in aerodynamics as "aerodynamic drag".
The effect of a roof rack on gas mileage has actually been scientifically proven. A study has been done, the first of its kind, to prove that a roof rack does affect gas mileage. Alan Meier, from the Lawrence Berkeley National Laboratory, together with Yuche Chen of the National Renewable Energy Laboratory (NREL), conducted a research which came up with some interesting results. Namely, they found that, in 2015, roof racks in the United States accounted for 0.8 percent of light-duty vehicle fuel consumption, which means that 100 million gallons of gasoline were used more, directly as a result of roof racks. This is quite a large number that undoubtedly has a significant effect on everyday lives of people.
Meier and Chen used a bottom-up approach in their study, and one of the conclusions was that results were most sensitive when it came to vehicles that had roof racks installed, but without any equipment to carry. The two researchers used online forums to collect data and also made extensive use of crowd sourcing. When conducting the research, they considered both loaded and unloaded racks. Additionally, they used nationwide highway video surveys, and also considered using toll booths as a source of information for determining what was on the roofs of the vehicles that passed through them. However, in the end, toll booths were not included, as the quality of the information wasn't conclusive.
Talking about the study, Meier said that he had always been intrigued by energy consumption that was somehow overlooked or ignored, such as the fuel consumption of vehicles equipped with after-market accessories. The study is the first one to cover the entire nation.
One of the conclusions of the research was that, by optimizing the design of roof racks, the energy savings could be substantial. The optimal thing, of course, would be to remove the roof racks altogether, but that's not always possible. If the use of unloaded roof racks could be minimized, together with energy-efficient designs, this could potentially mean a saving of 1.2 billion gallons of gasoline over the next 26 years, which is massive. However, this would take a lot of coordination, especially on the government side of things.