Cargo Boxes Will Change Your Gas Mileage This Much: Here is Why

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A rooftop box carrier is a feasible means of carrying additional gear on summer road trips or ski vacations in winter. But mounting these pods is likely to have an impact on your car as well as its fuel economy.

While cargo boxes are typically sleek and aerodynamically designed, they can yet affect the fuel economy of the car more than if you were driving it without anything mounted on the top.

If you aren’t someone to read through a complete article, the answer is: Cargo boxes can affect your gas mileage due to weight and aerodynamics. Likely you will lose about 17% of your vehicle’s normal gas mileage.

What are rooftop boxes?

Before we dig too far into if these boxes affect gas mileage, let’s quickly discuss what they are, for those that stumbled upon this article.

As the name suggests, rooftop boxes are hard-shelled boxes designed for carrying the extra load when you are going for some sport or adventure.

These are built to hold fishing rods, snowboards, and a host of other items. Some of them are even designed to be mounted directly without any roof rack.

Most of these carriers are devised to fit into a large variety of vehicles. This means you will not have to rummage through the store to find the one that suits your needs.

Once you find the right rooftop box (this is one we really like), you can install it permanently or detach it when not in use. And if you are concerned about the gas mileage, it is always better to have it removed when you are not using it for a while.

Do cargo boxes surge up fuel consumption?

Now that we know what a cargo roof box is, let’s talk more about if it affects gas mileage.

Having a cargo box attached to your vehicle is quite convenient. But if you are worried about whether these carriers have an impact on the gas mileage of the car, then you have come to the right place.

A lot of drivers notice an alteration in their gas mileage after installing a roof box or a rooftop box. This happens due to the additional weight on the top of the car which changes its aerodynamics.

Sometimes, having them installed also leads to considerable drag when there is much wind resistance. Thus, it becomes even more challenging to save money on mpg miles per gallon. 

The relation between vehicle drag and fuel consumption is directly proportional. And since it is greatly affected by the weight put on the roof of the vehicle, it will invariably result in using up more gas.

Other things are affecting the gas mileage as well including the design and size of the box.

Is there a connection between air flow and fuel consumption?

Airflow also correlates with fuel consumption. Now consider adding a rooftop box on the top of your car. The vehicle will become boxier disrupting the airflow and causing more drag. As a result, the gas mileage won’t be much effective.

This implies that you will end up increasing the fuel consumption with the rooftop box. For instance, if you get around 30 miles per gallon mileage to the vehicle, it will come down to around 25 miles per gallon on average.

The design and overall size of the carrier will also affect the amount of extra fuel usage. But it is safe to say that even if you have the smallest cargo box attached to your vehicle, there is going to be some impact on the gas mileage.

Even when your rooftop box is sitting there idle without carrying any load, it can subsequently bring down the mileage by around 5 mpg miles per gallon.

Is there a way to improve the mileage with the cargo box?

Even though most rooftop boxes will increase the fuel consumption of the vehicle, there are several ways by which it can be mitigated.

For instance, driving within the speed limit or around five miles under the limit can help you save fuel. This is because the lesser the driving speed, the lower will be the drag.

This, in turn, can improve the gas mileage. Thus, experts always suggest exercising caution when you are driving with a cargo box mounted on top.

While losing a small amount of gas due to the rooftop box may seem insignificant, it can have a major impact on your fuel economy in the long run.

Also, aerodynamically crafted rooftop (like this one) boxes offer better mileage and you should always look for such boxes. Last but not the least, it’s best to have them detached when you are not carrying anything in these rooftop boxes.

What are some of our favorite Roof Top Cargo Boxes?

If you are on the hunt for a cargo box, we put together a quick list of our favorites for you to take a look at yourself!

  1. YAKIMA RocketBox Pro
  2. Thule Force Rooftop Cargo Box
  3. SportRack Horizon Cargo Box

Frequently Asked Questions

Do hitch cargo carriers affect gas mileage?

As an alternative to the standard roof-mounted cargo box, hitch cargo carriers are an awesome, and sometimes a more usable option. Hitch cargo carriers do not have as much impact on gas mileage as rooftop boxes. This is because they are mounted at the back of the vehicle and do not disrupt the airflow. The downside to these is that it lengthens your vehicle, making it more difficult to park.

Do roof cargo boxes make noise?

These aerodynamic cargo boxes are built to be the most efficient as possible. However, with anything on a vehicle that doesn’t keep its factory shape, it might cause a few problems. Some people may find that their cargo boxes whistle a bit in the wind, and might rattle a bit due to the lid moving around a bit.

Do I need a crossbar for my roof box?

Roof cargo boxes do need crossbars to function correctly. These cross bars are what the cargo box sits on top of, and also adheres to. These are easy to purchase and install, and generally will come with a locking mechanism of their own.


To sum it up, a cargo box will have an impact on the gas mileage. But if you are driving carefully and keeping the box empty when not in use, then the effect will be minimal.

Just make sure to get a good quality box that is designed aerodynamically to ensure better fuel economy.