If you’re one of those who leave the cargo box on top of your car after a trip, you might be wondering whether it really matters. A cargo box is convenient, but driving with an empty one can actually affect your car’s performance more than you think.
Fuel Efficiency Takes a Hit
One of the most immediate effects of driving with an empty cargo box is a reduction in fuel efficiency. Your car becomes less aerodynamic, leading to increased drag. According to the U.S. Department of Energy, aerodynamic drag can significantly affect fuel consumption. In fact, it states that at highway speeds, more than 50% of the engine power goes towards overcoming aerodynamic drag.
Hauling cargo on the roof of a vehicle increases aerodynamic drag (wind resistance) and lowers fuel economy. A large, blunt roof-top cargo box, for example, can reduce fuel economy by around 2% to 8% in city driving, 6% to 17% on the highway, and 10% to 25% at Interstate speeds (65 mph to 75 mph).
https://www.energy.gov/energysaver/driving-more-efficiently
This drag becomes even more noticeable when you have a cargo box mounted on your roof. Based on tests conducted by Consumer Reports, a cargo box can lower fuel efficiency by as much as 5% to 25%, depending on the size and shape of the box. Imagine you’re driving at 65 mph; the drag created by an empty box can have the same effect as driving with extra passengers.
We did fuel-economy tests at highway speed in a Nissan Altima and Toyota RAV4 with a roof rack, tail-hitch rack, and rooftop box. Carrying two mountain bikes on the roof had the biggest impact. The Altima lost 13 mpg, going from 46 mpg to 33 mpg. The RAV4 lost 7 mpg, dropping to 32 mpg from 39 mpg.
https://www.consumerreports.org/cars/fuel-economy-efficiency/10-tips-to-get-the-most-out-of-a-tank-of-gas-a2642110189/
Wind Resistance and Safety Concerns
When you’re driving at high speeds, wind resistance increases exponentially. An empty cargo box increases the surface area of your vehicle, making it more susceptible to crosswinds. In some cases, this can make your car less stable, especially on highways or during windy conditions.
Several drivers have reported on forums that their vehicles became harder to control during windy weather. Though this isn’t always a significant concern, it’s something you should consider if you’re planning on long-distance highway trips. The extra surface area on your roof means more exposure to wind forces, which can affect the handling of your car.
Cost Over Time
Even if you don’t drive long distances frequently, the long-term costs of reduced fuel efficiency will add up. Based on average U.S. fuel prices and the data from the American Automobile Association (AAA), losing 10% fuel efficiency could cost you around $100–$200 more per year if you drive 12,000 to 15,000 miles annually. Over the course of several years, that extra fuel consumption really starts to eat into your wallet.
The Wear and Tear on Your Car
Driving with a cargo box also means extra wear and tear. The roof of your vehicle wasn’t designed to hold something that adds significant drag at all times. Some drivers have reported that continuous use of a roof box caused their roof racks to weaken or loosen. You may find the fittings getting worn out over time, leading to potential repairs or replacements. Moreover, any movement in the cargo box could scratch your car’s roof, damaging the paint and exposing the metal to rust.
Another concern raised by users is the added stress on the suspension and tires. Even when the cargo box is empty, the distribution of weight on the vehicle changes. Over time, this may lead to slightly faster wear on your suspension system, though the effect may vary based on the type of car and box you’re using.
Noise Pollution
A less obvious effect of driving with an empty cargo box is the noise. Roof boxes tend to create a lot of wind noise, especially at highway speeds. This is something drivers commonly report. Depending on how sensitive you are to noise, it can make long drives less comfortable. Certain models of roof boxes are better at reducing noise, but in general, any box will produce some level of sound due to wind resistance.
According to various driver reports, the noise can range from a subtle hum to a louder, more intrusive sound, particularly if the box isn’t well-secured or if it’s not aerodynamic. Over time, this constant noise can become an annoyance, especially if you’re someone who likes a quiet cabin during long trips.
Environmental Impact
Not only is driving with an empty cargo box bad for your wallet, but it’s also bad for the environment. Increased fuel consumption leads to more carbon emissions. The Environmental Protection Agency (EPA) states that burning a gallon of gasoline produces about 19.6 pounds of carbon dioxide. If a cargo box reduces your fuel efficiency by even 10%, your carbon footprint could increase substantially over the course of a year.
A typical passenger vehicle emits about 4.6 metric tons of CO2 per year. This assumes the average gasoline vehicle on the road today has a fuel economy of about 22.2 miles per gallon and drives around 11,500 miles per year. Every gallon of gasoline burned creates about 8,887 grams of CO2.
https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle
For those who are environmentally conscious, removing the cargo box when it’s not in use is a small step toward reducing unnecessary emissions.
Insurance and Legal Considerations
In some states, having an empty cargo box on your car may affect your insurance premiums. Since the box alters your vehicle’s aerodynamics and handling, it could be considered a “modification” by some insurance providers. Always check with your insurer to see if they have specific policies related to cargo boxes or any other attachments on your vehicle.
Moreover, laws regarding vehicle height and weight limits vary. Make sure your cargo box doesn’t exceed the legal limits for vehicle height in your area. Even an empty box adds height to your car, and this could lead to fines in some states.
When Should You Take the Box Off?
So, should you leave your cargo box on your vehicle? The general consensus from most experts is that you should remove it when not in use. Not only will it save you money on fuel, but it will also reduce wear and tear on your car, lower noise levels, and help the environment.
If you frequently use your box for commuting or short trips, it might be tempting to leave it on for convenience. But in the long run, it’s better to only install it when you actually need it. Many drivers share that they’ve noticed a significant difference in their vehicle’s performance and fuel efficiency after removing the box.
Conclusion
Driving with an empty cargo box comes with more downsides than you might think. From fuel efficiency drops to increased noise and wear on your vehicle, the costs can add up. It’s always worth the few minutes it takes to remove the box when you’re not using it, especially if you drive long distances or frequently use highways.
In the end, whether it’s about saving money, reducing environmental impact, or simply having a quieter ride, the benefits of removing the empty cargo box outweigh the convenience of keeping it mounted.
