Do roof racks reduce MPG?
Yes. Roof racks typically reduce fuel economy, especially on highway driving, and the amount depends on the rack type, cargo, vehicle, and driving speed.
Why roof racks affect fuel economy
Roof racks disrupt the smooth flow of air over a vehicle and add drag. Even without cargo, the presence of crossbars and rails increases aerodynamic resistance; adding a box or heavy load magnifies that drag and forces the engine to work harder, particularly at higher speeds.
Understanding the main factors helps explain why the mpg impact varies and how drivers might estimate the effect on their own trips.
The following factors help explain why fuel economy declines when you carry gear on the roof and how big the drop can be.
- Aerodynamic drag increases with crossbar width and rooftop exposure
- Racks add weight, but drag is usually the bigger factor than the extra mass
- A cargo box increases drag more than an open rack does
- Higher driving speeds dramatically amplify drag and fuel use
- Vehicle shape and size influence sensitivity; small cars and tall SUVs respond differently
- Load distribution and wind direction can affect drag and stability
In practice, the mpg hit tends to be larger on highway trips and smaller in city driving, with the possibility of a noticeable decrease if a heavy box is used at high speeds.
Quantifying the impact
Tests and vehicle data show a range of potential effects depending on setup and speed. The exact number varies by car, rack design, and how fast you drive.
- Bare roof rack with no cargo: typical highway mpg decrease is roughly 2–5% for many cars
- Racks with a lightweight cargo box: additional drop often in the 5–15% range, depending on speed and box design
- Heavy roof loads or poorly shaped cargo: drag increases can push losses into the high single digits to around 20% at highway speeds
- Speed sensitivity: the penalty grows with speed; the difference between 60 mph and 75 mph can be substantial
Real-world results vary widely, and removing the rack when not needed is often the simplest way to recover fuel economy. If you must use a rack, choosing aerodynamically designed gear and keeping speeds moderate helps minimize the hit.
Minimizing the MPG hit
Carrying gear on the roof doesn't have to ruin your trip—there are practical steps to reduce drag and save fuel.
Remove racks when not in use
Storing or removing crossbars and boxes when you’re not carrying gear can recover a meaningful amount of efficiency, especially on highway driving.
Choose aerodynamic gear
Opt for low-profile crossbars and aerodynamic roof boxes designed to minimize drag. Some boxes are shaped to cut wind resistance and can significantly reduce the penalty compared with older, boxy designs.
Drive at moderate speeds and plan routes
Drag increases with speed, so keeping highway speeds in check and maintaining steady acceleration can help lessen fuel penalties. Planning routes to minimize long highway legs with roof cargo can also help.
Summary
Roof racks generally reduce MPG due to added aerodynamic drag, with the magnitude depending on the vehicle, rack design, cargo, and driving speed. Bare racks without cargo have a smaller impact; adding a cargo box or heavy roof load increases the penalty, especially at higher speeds. To minimize the hit, remove racks when they’re not needed, choose aerodynamic gear, and drive at moderate speeds. Real-world results vary, so testing your own vehicle—if feasible—can provide the most accurate estimate for your setup.
How much extra fuel does an empty roof rack use at 70 mph?
The excess drag from leaving an unused roof box and rack on your car can cost you between 13% and 19% more in fuel according to the car you are driving. Save fuel and money by removing unused roof boxes and bike racks.
How does a roof rack affect fuel consumption of a car?
After years of testing different setups on my vehicles and gathering data from fellow enthusiasts, I've found that the fuel economy impact of roof racks breaks down approximately as follows: Empty roof rack bars only: 2-5% decrease in fuel economy. Partially loaded roof rack: 6-15% decrease.
What are the cons of roof racks?
Downsides of Car Roof Racks
Roof racks aren't perfect. If you're planning to get one, you must know that it can affect aerodynamics and strain the engine. It's also not ideal for small vehicles, it can damage the vehicle, and it could affect handling.
What trick gives you the best gas mileage?
Here are a few recommended models that consistently deliver strong MPG ratings:
- Ram 1500 EcoDiesel (2014-2022) – Up to 22 MPG city / 32 MPG highway.
- Chevrolet Colorado Diesel (2016-2022) – Up to 20 MPG city / 30 MPG highway.
- Ford Ranger (2019-2024) – Up to 21 MPG city / 26 MPG highway.
