Tested: How Rooftop Boxes and Hitch Carriers Affect Fuel Economy
In working to find the best hitch-mounted cargo carriers, we tested to see how roof boxes and hitch-mounted carriers affect fuel consumption
We ran back-to-back tests with our long-term Toyota Grand Highlander, first carrying a Yakima EXO SwingBase hitch carrier, then a Thule roofbox.
The hitch-mounted carrier was the clear winner, returning 25 mpg compared with 21 mpg for the rooftop carrier.
Welcome to Car and Driver's Testing Hub, where we zoom in on the test numbers. We've been pushing vehicles to their limits since 1956 to provide objective data to bolster our subjective impressions (you can see how we test here).
If you've ever looked at an electric car and wondered why so many of them have flush-mounted door handles, the reason is to reduce aerodynamic drag. It's the same reason you see cyclists wearing funny helmets and Olympic speed skaters wrapped in skin-tight spandex. It's also why hitch-mounted cargo carriers are generally viewed as a more fuel-efficient alternative to rooftop carriers. Since our Gear Team was already working on a test of the best hitch-mounted carriers, we decided to put the numbers to the test to see just how much more fuel a roof box burns.
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Michael Simari
To keep things fair, we ran back-to-back highway fuel-economy tests on our long-term Toyota Grand Highlander. For the hitch-mounted test, we selected the Yakima EXO SwingBase carrier equipped with Yakima's GearLocker. The carrier and locker weigh 93 pounds combined and together measure 59.5 inches wide.
As for the roofbox, we pulled an older Thule model down from the storage rafters in our HQ garage and then mounted it to a set of Thule SquareBar Evo crossbars. The box itself weighed 42 pounds and measured 90.0 inches long.
The test results were clear: The Grand Highlander averaged 25 mpg with the hitch-mounted carrier but only 21 mpg with the rooftop box attached, a significant 4-mpg difference.
Michael Simari
Michael Simari
We ran a similar test on our long-term 2022 Kia Carnival back in 2023. After continuing to be disappointed by subpar fuel-economy figures, we decided to do some digging and test the Carnival with and without the factory crossbars. With the crossbars attached, our initial highway fuel-economy test returned 25 mpg. With the bars removed, that number jumped to 28 mpg.
Jack Fitzgerald
Associate News Editor
Jack Fitzgerald's love for cars stems from his as yet unshakable addiction to Formula 1.
After a brief stint as a detailer for a local dealership group in college, he knew he needed a more permanent way to drive all the new cars he couldn't afford and decided to pursue a career in auto writing. By hounding his college professors at the University of Wisconsin-Milwaukee, he was able to travel Wisconsin seeking out stories in the auto world before landing his dream job at Car and Driver. His new goal is to delay the inevitable demise of his 2010 Volkswagen Golf. Read full bio
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