Even if you own an already large vehicle, roof-rack carrier boxes are surprisingly useful. They hold extra luggage, sleeping bags, and even snow skis. But when you’re not making like Clark W. Griswold on a family journey, is it okay to just drive around town with the box on the roof?
There’s nothing inherently wrong with leaving your carrier box on all the time. So long as the storage add-on is secure, it’s going to be fine. But the more appropriate choice is to remove the box. By doing so your car will be more aerodynamic, won’t tote unnecessary weight, and will burn less fuel.
Take the box off when you’re not using it; your car will thank you, and so will your wallet. But if you do insist on leaving the carrier box on, there are some details to be aware of. What exactly happens when you love your carrier so much that the idea of leaving it behind is unbearable?
Leaving a Carrier Box on a Car
Just about everyone who flat out refuses to believe carrier boxes can be left on a car will point to the most obvious reason: fuel consumption. Indeed, the more weight your car has to carry, the more gas it’s going to burn. The same goes for charge distance on an EV—it’ll decrease.
Fuel
The hit you take will vary depending on how heavy and aerodynamic the carrier box is. Quite so, carrier box manufacturers are not blind to the fact. Note that many of today’s boxes are not really boxes at all, but teardrop-shaped to look more like a sleek turtle shell.
In 2017, an engineering team in Malaysia conducted a wind tunnel test using a simulated aerodynamic roof box. A 34% reduction in drag force was noted on the object the box was attached to; 34% equated to a 1.7% fuel economy boost for the time.
Here’s a little more data: A 2009 Toyota Corolla going 65 miles (104 km) per hour got around 40 miles (64 km) per gallon. With an empty 50-pound (22 kg) cargo box on the roof, that mileage drops to 35 miles per gallon. It’s a great reason not to always leave your carrier on the roof.
“But I drive an EV!” I hear some of you saying. “Elon Musk is my hero!” So let’s find out how carrier boxes affect electric vehicles.
Electric Vehicle Range
How box carriers affect the range of an EV turned out to be surprising. Tesla in particular makes their own roof rack, plus the boxes. The company recommends installing the box with the thin end over the driver’s seat.
This method results in a 16% hit on the car’s mileage range. Now here’s the interesting part: A Tesla Model 3 fan in Sweden flipped the box, so the wide end was over the driver’s seat…and got all of that 16% back! That’s right—his range became equal to the range he got with no box installed.
With this information, carrier boxes pose no significant impact on EV range so long as the box is mounted correctly (or, by Tesla’s advice, incorrectly). Then again, it is worth noting that different boxes will have different range effects from EV to EV.
Other Issues with Rooftop Carrier Boxes
Fuel and energy consumption are the two biggest reasons to avoid leaving cargo boxes on a roof rack. Are there any more concerns? Yeah, I can think of a couple.
Modern carrier boxes won’t add too much height to the roof of your car (manufacturer Thule’s smallest box tacks on an extra 50 centimeters, or just under 20 inches). Still, I can’t suggest you blithely charge under a low clearance railroad trestle or pick up some burgers and fries at a covered drive-thru.
There’s always a chance of the box making contact with the ceiling. Broken pieces could fly off to damage other vehicles—or worse, do harm to a living soul. At best, you’ll end up having to replace your box, plus become an object of ridicule among your peers.
Speaking of ridicule: Leaving a rooftop box carrier on a car all the time is just tacky, like wearing bunny slippers to a funeral or driving Greta Thunberg to school in a Chevy Suburban. Other drivers might think you’re on an adventure of some kind, but your friends will know the truth.
There are better places for that box to be when you’re not using it. Like where? Let’s find out.
Removal and Storage of Carrier Boxes
Rooftop carrier boxes are very easy to remove. The modern ones have locking mechanisms that come unscrewed with the twist of a wrist. From there, it’s a simple matter of lifting the box off the roof.
This video shows an example of how to do this.
Note that at 50 seconds he mentions damaging the carrier at a car wash. Even the most knowledgeable drivers can forget about ground clearance from time to time.
Once off, you can store carrier boxes in a shed or garage. Don’t worry—they will wait quietly for your next road trip. And you’ll prolong the life of your box, plus get better gas mileage from the pump.
Rooftop Carrier Box Tips
Lastly, I have a few quick tips about these carrier boxes that every user should be reminded of. We’ve covered fuel consumption and ground clearance, but don’t forget to:
- Make sure your vehicle can carry the extra weight
- Adjust tire pressure for the extra weight
- Inform your insurance company that you have modified your car
Now you’re set to go. Have a safe trip.
Conclusion
It’s okay to always leave your rooftop carrier box on so long as you take the right precautions. That said, storing these units when not in use is a wiser course of action. It only takes about ten minutes to remove one. The time and preserved character are well worth the effort you put in.
Sources
- Good Housekeeping: 6 Best Rooftop Cargo Carriers of 2022, According to Testing
- EDP Sciences: Roof Box Shape Streamline Adaptation and the Impact towards Fuel Consumption
- Motor Biscuit: Your Roof Cargo Box Is Ruining Your Car’s MPG More Than You Think
- Electrek: Tesla Model 3 with roof-rack box gets much better range if you flip box aroun
- Roofbox2hire: Thule S Roof Box
