Yes. Roof crossbars can reduce fuel efficiency, especially at highway speeds or when carrying cargo. The magnitude of the drop varies by vehicle, bar design, and usage.
Crossbars disturb airflow over the roof, creating drag that your engine must overcome. The penalty grows with speed and payload, and it can be more noticeable on some cars than others.
How crossbars affect fuel efficiency
Drag from the roof adds to the car’s overall drag and can lower miles per gallon. The impact depends on bar type, load, and driving conditions. Below are the main factors that determine how large the effect is.
Here are the main variables that influence how much your mpg is affected when using crossbars:
- Speed: Drag increases with speed, so highway driving amplifies the mpg penalty more than city driving.
- Bar design: Aerodynamic, low-profile crossbars reduce drag more than traditional, boxy bars.
- Load and cargo: Carrying gear or a roof box increases the cross-sectional area and turbulence, worsening the drag effect.
- Vehicle type and baseline efficiency: Smaller, more aerodynamically efficient cars often show a relatively larger percentage drop than heavier SUVs, though the absolute mpg loss can be significant on any vehicle at speed.
- Installation and alignment: Properly installed bars that are centered and follow the roof shape minimize unwanted drag; misaligned or loose bars can worsen drag.
Real-world estimates vary, but common ranges are: unloaded crossbars can reduce highway mpg by roughly 1–3% for many sedans and about 2–5% for larger vehicles; adding a roof cargo box or heavy cargo can increase the penalty to roughly 5–15%, and in windy conditions or at very high speeds, the effect can be higher.
In summary, crossbars themselves create drag, and the more you load them or ride at higher speeds, the greater the mpg impact. The effect is usually modest for unloaded crossbars on many vehicles, but becomes substantial when a cargo box or bulky payload is added, especially at highway speeds.
Minimizing the mpg impact
To keep fuel use in check, consider these strategies that reduce the aerodynamic penalty of roof racks:
- Remove crossbars when you’re not using them. This is the most effective way to regain mpg.
- Choose aerodynamic crossbars and, if possible, integrated rails designed to minimize wind resistance.
- Avoid using a roof cargo box unless you need to; even empty, a box adds significant drag compared to bare crossbars.
- Keep cargo to a minimum and avoid overhangs or loose items that catch the wind.
- Ensure proper installation per manufacturer instructions to maintain a clean, drag-friendly profile.
Implementing these practices can noticeably improve efficiency on long trips or when fuel economy is a priority. The most impactful step remains removing the crossbars entirely when they’re not needed.
Summary
Crossbars and roof-mounted gear introduce aerodynamic drag that lowers MPG, especially at highway speeds and with cargo loaded. The impact is typically modest for unloaded crossbars—roughly a couple of percent—while cargo boxes and bulky gear can push the penalty into the double-digit range in favorable conditions. To minimize the effect, remove crossbars when not in use, opt for aero designs, and limit or avoid roof cargo unless necessary. Driving at moderate speeds and maintaining efficient driving habits also helps offset the drag penalty.