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Adding a cargo box is an easy way to gain storage, but many Crosstrek, Forester, and Outback owners wonder how much it affects fuel economy.
While cargo boxes can reduce MPG, the impact depends more on speed and aerodynamics than weight. Highway driving typically shows the biggest difference.
For most owners, the tradeoff is worth it. Extra storage can make road trips and everyday travel more comfortable and practical.
Understanding what affects fuel economy can help you choose a setup that balances efficiency with convenience.
Yes, Cargo Boxes Can Reduce Fuel Economy
Why Aerodynamics Matter More Than Weight
For most Crosstrek, Forester, and Outback owners, aerodynamic drag has a greater effect on fuel economy than the weight of the cargo box itself. Even an empty box changes airflow and creates additional resistance.
Box shape and overall height often have a bigger impact on MPG than the amount of gear being carried.
Highway Driving Has The Biggest Impact
Fuel economy losses are usually more noticeable at highway speeds. As speed increases, the vehicle must work harder to overcome the added drag created by the cargo box.
Many owners notice little difference around town but see a larger impact during long highway trips.
Some MPG Loss Is Normal
A reduction in fuel economy is a normal tradeoff for gaining additional storage. The exact amount varies depending on speed, vehicle, cargo box size, and overall setup.
For most owners, a modest decrease in MPG is expected and simply becomes part of using a roof-mounted cargo box.
How Much MPG Loss Is Typical?
City Driving
In city driving, many Crosstrek, Forester, and Outback owners notice little change in fuel economy. Lower speeds create less aerodynamic drag, so the impact of a cargo box is usually modest.
Highway Driving
Highway driving typically produces the largest reduction in MPG. Higher speeds increase aerodynamic resistance, making fuel economy losses more noticeable during everyday commuting and longer drives.
Road Trips
During extended road trips, many owners see a measurable decrease in fuel economy compared with driving without a cargo box. The exact impact depends on speed, weather conditions, and how heavily the box is loaded.
Why Results Vary
Fuel economy losses vary from one setup to another. Vehicle speed, cargo box shape, crossbar design, wind conditions, and overall load all influence the results.
For most owners, some reduction in MPG is normal, but the exact amount can differ significantly depending on how the vehicle is used.
| Driving Situation | Typical MPG Impact |
| City Driving | Minimal |
| Mixed Driving | Small |
| Highway Driving | Moderate |
| Long Road Trips | Most Noticeable |
What Affects Fuel Economy The Most?
Vehicle Speed
Vehicle speed has the biggest impact on fuel economy. As highway speeds increase, aerodynamic drag rises significantly, making cargo boxes more noticeable in terms of MPG loss.
Cargo Box Size
Larger cargo boxes generally create more drag and may reduce fuel economy more than smaller models. However, size alone does not determine the overall impact.
Cargo Box Shape
Shape often matters more than capacity. Lower-profile, streamlined boxes usually disturb airflow less than taller or boxier designs, helping minimize MPG losses.
Crossbar Design
Crossbars influence airflow and can affect fuel economy. Lower-profile aerodynamic bars tend to create less drag, while wider or less streamlined designs may have a greater impact.
Overall Load
The amount of weight carried inside the cargo box also affects fuel economy. Heavier loads require more energy to move, though aerodynamic drag usually has a larger effect than weight for most Crosstrek, Forester, and Outback owners.
Do Larger Cargo Boxes Hurt MPG More?
Small And Medium Boxes
Small and medium cargo boxes generally have a smaller impact on fuel economy. Their lower profile and reduced surface area help minimize aerodynamic drag, making them easier to live with during everyday driving.
Large Boxes
Large cargo boxes typically create more drag and may result in greater MPG losses, especially at highway speeds. However, the difference is not always dramatic and depends heavily on the overall design.
Why Height Matters More Than Capacity
Two boxes with similar capacities can affect fuel economy differently. Taller boxes often create more resistance than longer, lower-profile designs, making overall shape more important than cubic-foot ratings.
Bigger Isn’t Always Better
Extra storage is useful, but larger boxes also bring tradeoffs. For many Crosstrek, Forester, and Outback owners, choosing a box that matches their typical needs results in a better balance between cargo space and fuel economy.
Crosstrek vs Forester vs Outback
Crosstrek Considerations
The Crosstrek’s smaller size and lower profile can help minimize aerodynamic drag. However, cargo boxes represent a larger percentage of the vehicle’s overall frontal area, so MPG losses can still be noticeable during highway driving.
Forester Considerations
The Forester’s taller shape provides excellent interior space but may expose the cargo box to more airflow. As a result, fuel economy losses can become more apparent, particularly with larger or taller boxes.
Outback Considerations
The Outback’s longer roof and lower profile often work well with cargo boxes. Longer, lower-profile boxes can be positioned more effectively, helping balance storage capacity with fuel efficiency.
Which Subaru Experiences The Least Impact?
No model consistently experiences the least MPG loss. Vehicle speed, cargo box shape, and roof rack design usually have a greater effect than the vehicle itself. With a streamlined setup, Crosstreks, Foresters, and Outbacks can all maintain reasonable fuel economy.
Leaving A Cargo Box Installed Year-Round
Daily Driving Considerations
Many Crosstrek, Forester, and Outback owners leave their cargo box installed year-round. While convenient, it can affect fuel economy, wind noise, garage clearance, and overall vehicle height during everyday driving.
Why Many Owners Remove The Box
Some owners remove the cargo box when it is not needed to reduce wind noise and improve fuel efficiency. Removing the box can also make parking and garage access less complicated.
Convenience Versus Efficiency
Keeping a cargo box installed provides instant access to additional storage, but it comes with tradeoffs. For many owners, the decision depends on how often the extra space is actually used.
Storage Considerations
Removing a cargo box requires having a place to store it. Garage space, wall mounts, and ceiling storage systems can all influence whether leaving the box installed year-round is the most practical option.
Mistakes That Can Make MPG Worse
Driving Faster Than Necessary
Higher speeds increase aerodynamic drag and magnify the effect of a cargo box. For many Crosstrek, Forester, and Outback owners, highway speed has a greater impact on MPG than the weight inside the box.
Using A Larger Box Than Needed
Oversized cargo boxes create more drag and may reduce fuel economy unnecessarily. Choosing a size that matches your typical needs often provides a better balance between storage and efficiency.
Carrying Unnecessary Weight
Extra gear adds weight and forces the vehicle to work harder. Keeping only essential items in the cargo box can help minimize unnecessary fuel consumption.
Leaving Unused Accessories Installed
Unused bike racks, kayak carriers, and other roof-mounted accessories create additional drag even when they are empty. Removing components that are not being used can help improve both fuel economy and everyday comfort.
Is The MPG Loss Worth It?
Why Families Often Accept The Tradeoff
Many families are willing to sacrifice some fuel economy in exchange for additional storage. Extra space can make it easier to bring strollers, luggage, and outdoor gear without overcrowding the cabin.
Road Trips Become Easier
A cargo box helps free up interior space and reduces the need to pack as tightly. For many owners, the added convenience outweighs the cost of a few MPG.
Passenger Comfort Improves
Moving bulky items to the roof allows passengers to enjoy more legroom and a less cluttered cabin. This can make long drives more comfortable for both adults and children.
Practicality Usually Outweighs The Cost
Most Crosstrek, Forester, and Outback owners view some MPG loss as a reasonable tradeoff for increased versatility. In many cases, the added convenience and usability are worth more than maximizing fuel economy.
What Actually Works (Based On Real Use)
Most Owners Accept The Fuel Economy Penalty
Most Crosstrek, Forester, and Outback owners consider some MPG loss a normal tradeoff for the added storage and flexibility a cargo box provides.
Speed Matters More Than Weight
Highway speed usually has a greater effect on fuel economy than the weight inside the box. Slower speeds generally help minimize MPG losses.
Properly Sized Boxes Help
Choosing a box that matches your typical needs helps balance storage and efficiency. Oversized boxes often provide little additional benefit while increasing drag.
Convenience Usually Matters More Than A Few MPG
For many owners, the extra cargo space and improved passenger comfort outweigh the cost of losing a few miles per gallon. Practicality often matters more than maximizing efficiency.
FAQs
How much MPG does a cargo box reduce?
Most owners see a small reduction, with highway driving showing the biggest impact.
Do cargo boxes hurt gas mileage?
Yes. Cargo boxes increase aerodynamic drag, which reduces fuel economy.
Does highway speed affect fuel economy more?
Yes. Higher speeds have a greater effect on MPG than city driving.
Do larger cargo boxes reduce MPG more?
Generally yes, though box shape and height often matter more than capacity.
Does weight or aerodynamics matter more?
Aerodynamics usually have a bigger impact than weight.
Should I remove my cargo box when not using it?
For many owners, yes. Removing the box can improve MPG and reduce wind noise.
Which Subaru loses the most MPG with a cargo box?
There is no consistent winner. Box design and driving speed matter more than the vehicle itself.
Does a cargo box affect city driving?
Yes, but the effect is usually smaller than during highway driving.
Are cargo boxes worth the fuel economy penalty?
For many owners, the added storage and convenience outweigh the loss in MPG.
Do crossbars affect MPG too?
Yes. Crossbar shape and exposed overhang can contribute to additional drag.
Final Thoughts
Cargo boxes do affect MPG, but for most Crosstrek, Forester, and Outback owners, the tradeoff is worth it.
The best setup depends on how you use your Subaru. Choosing the right box size and overall setup often matters more than maximizing fuel economy.
As your needs change, factors like box size, crossbar design, and year-round use become just as important as storage capacity.
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Related Guides
• How to Stop Cargo Box Wind Noise
• Cargo Box Height Garage Clearance Guide
• How to Pack a Cargo Box Efficiently
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