Roof boxes are an essential tool for anyone needing extra storage on road trips, camping adventures, or simply transporting gear. But the question of whether the roof box should be centered or not plays a critical role in your vehicle’s safety, fuel efficiency, and overall handling. Here’s an in-depth look at why centering a roof box matters and how to ensure it’s done correctly.
Why Positioning Matters: The Science of Balance
When you mount a roof box, placing it in the center ensures your vehicle remains balanced. This balance affects handling, particularly when taking turns or driving on uneven roads. According to a study by the National Highway Traffic Safety Administration (NHTSA), unbalanced loads on vehicles increase the likelihood of accidents, especially during sharp turns or emergency maneuvers.
Unsecured loads not only endanger you, but also other drivers and pedestrians. Each year, about 730 people are killed and 17,000 more are injured because of objects in the road. Most of these crashes (81%) involve unsecured loads on passenger vehicles.
https://www.nhtsa.gov/drive-safe-secure-your-load
In simple terms, when weight is distributed evenly across the top of the car, it maintains stability. If the roof box is placed off-center, it may cause uneven pressure on one side, leading to unpredictable vehicle behavior. Proper weight distribution is critical to prevent accidents.
Aerodynamics and Fuel Efficiency: What the Data Says
One of the major considerations when installing a roof box is how it affects your vehicle’s aerodynamics. Roof-mounted boxes increase the car’s drag, which can raise fuel consumption by as much as 25%. Proper placement—ideally centered—can minimize this drag by allowing air to flow symmetrically over both sides of the box.
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
A centered roof box allows air to pass evenly across the vehicle, reducing turbulence. Improperly positioned roof boxes, especially if they are too far to the side, disrupt the aerodynamics and can significantly increase your fuel consumption. Tests have shown that poor aerodynamics can cost you 5-10% more on fuel, particularly at highway speeds.
Impact on Vehicle Handling
Weight distribution on a vehicle, particularly on the roof, impacts how it handles on the road. An imbalanced load can make the car feel unstable, especially when making turns or during sudden stops. Placing a load incorrectly—whether too far back, forward, or to the side—can negatively impact a vehicle’s center of gravity, increasing the risk of losing control.
The centre of gravity’s position is important when calculating the vehicle dynamics, and it affects the vehicle driving performances3. The distance between the centre of gravity and the axles are highly affected by their load. If the centre of gravity is too close to one of the axles, it may lead to its overload.
https://www.nature.com/articles/s41598-023-48083-8
By centering the roof box, you can help maintain the vehicle’s stability, ensuring that it responds as expected to steering inputs. Uneven weight distribution might lead to tire wear issues, suspension strain, and difficulty maintaining straight-line stability during windy conditions.
How Centering Affects Long-Distance Travel
On long road trips, fuel efficiency isn’t the only concern. Wind resistance and handling during extended periods on highways can significantly affect your overall driving experience. Off-center roof boxes can create additional wind noise, as well as added drag that tires out the driver over long stretches. The constant drag can lead to higher fatigue levels, especially if driving through windy or hilly terrain.
By positioning the roof box centrally, you can reduce the effects of wind drag and improve overall driver comfort during long journeys.
Exceptions to Centering a Roof Box
While centering is the best practice in most cases, certain vehicle designs may require an off-center placement. For instance, vehicles with sunroofs or moonroofs might not allow for a fully centered roof box due to size constraints. Additionally, cars that also carry roof-mounted accessories, such as bicycles or kayaks, may require the box to be shifted slightly to accommodate the extra gear. However, such adjustments should be minimal to avoid significantly impacting the car’s balance.
Any adjustments to the roof box’s position should still follow the basic principle of keeping the weight distributed as evenly as possible. In such cases, ensure that the roof box is properly secured, and its weight is balanced within the box itself.
Steps for Correct Roof Box Installation
Installing a roof box correctly requires a few key steps to ensure safety and efficiency:
- Check the vehicle’s roof load capacity: Every vehicle comes with a recommended roof load limit. Overloading the roof, whether the box is centered or not, can damage the roof or affect vehicle handling.
- Ensure balanced loading within the roof box: Even if the box is centered, uneven weight distribution inside the box can still lead to balance issues. Place heavier items in the middle of the box and ensure that all items are securely strapped.
- Test before hitting the road: After installing the roof box, take a short drive to ensure that it’s secure. Listen for unusual noises, particularly wind noise, which could indicate improper placement.
Conclusion
So, should a roof box be centered? Based on verified data from transportation experts and government bodies, the answer is a strong yes. Centering the roof box helps maintain vehicle balance, ensures fuel efficiency, and improves handling and safety. Unless there’s a valid reason to shift the box slightly (like space constraints from other roof-mounted gear), always aim to center the box.
