Do ski racks and roof boxes hurt fuel efficiency? Yes, more than you think.
Adding any rooftop carrier, cargo box, or ski rack to your car significantly cuts your highway mileage all the time it鈥檚 installed, whether there's weight up there or not.
Snow skis, poles and luggage are attached to a 1970 Volkswagen Porsche Speedster replica while the car sits in the sold lot during the Mecum car auction in Monterey, Calif. Attaching anything to the roof of a car will cut its mpg rate significantly, but some original-equipment roof-rack designs are better as they were designed specifically with that model in mind. REUTERS/Michael Fiala (UNITED STATES - Tags: SOCIETY TRANSPORT BUSINESS)
Michael Fiala/Reuters/File
If you follow our coverage on fuel efficiency, you know that聽聽to the official EPA ratings.
But if you think failing to meet those EPA numbers by five or ten percent is already a letdown, be very careful about your cargo-carrying expectations in your next sedan, hatchback, or crossover.
Adding any rooftop carrier, cargo box, or ski rack doesn鈥檛 come free. In fact, it significantly cuts your highway mileage all the time it鈥檚 installed, whether there's weight up there or not.
As the British magazine聽聽recently found, adding properly fitted roof boxes and a modest amount of cargo to a couple of compact family models decreased their effective gas mileage by up to 35 percent on the highway, versus official figures.
Of course it鈥檚 always been that way. Adding any roof box increases frontal area of your, of course; but no matter how aerodynamic it might look, it also alters the flow of air around your carefully shaped, wind-tunnel tested vehicle鈥攃reating drag and turbulence that can, together, knock 10 mpg off the mileage of a smaller four-cylinder vehicle.
What Car?聽used two models for testing鈥攁 Dacia Logan, and a Nissan Qashqai; the latter is a model that鈥檚 somewhat related to our Nissan Rogue. The magazine found that while the Qashqai is rated 39.2 mpg (in U.S. gallons) by European standards, it only achieved 26.7 mpg in real-world testing, 鈥渟cientifically calculated by experienced engineers.鈥�
This editor, many years ago, in a move across the country to Oregon from Michigan, found that the highway mileage of a four-cylinder聽聽dropped from more than 40 mpg down to 32 mpg with a modestly packed roof carrier.
Any roof carrier will cut your mpg, significantly
The same, of course, applies to roof racks and other cargo accessories. Even though they might look like they 鈥榗ut鈥� through the wind, they could be introducing some mileage-robbing turbulence and drag on the highway.
Some original-equipment roof-rack designs are better as they were designed specifically with that model in mind. Many also now allow you to swing the crossbars of the rack lengthwise when it鈥檚 not in use; if you have that feature, use it.
That said, roof boxes that aren鈥檛 completely necessary聽are聽costing you and the environment. Leaving a roof box on your vehicle on a regular basis could cost you big; and if you need it often, maybe it鈥檚 time you look into getting a bigger vehicle. Longer, more spacious聽, for instance, aren鈥檛 usually that much less fuel-efficient than subcompact ones on the highway.
And in some cases, for a long highway trip, it might be more fuel-efficient to tow a small trailer instead.
As always, we recommend checking real-world mileage logs鈥攖hrough聽聽and at the聽鈥攆rom those who own and drive聽聽daily, to understand the variance you might see in your own results.