Roof of Rear cargo box? Extending Your Travel Range for Weekend Escapes

Have you ever wondered how your storage units in your car affect your fuel economy on your weekend family trip? From bulky roof racks to sleek rear-mounted carriers, the choices we make about cargo storage can have surprisingly significant impact on our vehicle’s efficiency.

What are the numbers behind it?

In the realm of aerodynamics, even seemingly minor alterations can wield significant influence on vehicle performance and efficiency. Our recent simulations, comparing two Tesla cars—one with a storage box mounted on the roof and the other with the box positioned behind the car—underscore this principle vividly. At a speed of 25m/s (90km/h), the differences in aerodynamic parameters were striking. The car with the storage box behind experienced reduced drag force, meaning a lower coefficient of drag (Cd) of 0.414, compared to its rooftop counterpart, which had a Cd of 0.428. A lower Cd translates to a lower resistance the engine has to overcome to maintain the speed of the car constant.

How does the flow actually behave around my car?

Understanding these disparities requires a closer examination of airflow dynamics. When a storage box is placed on the roof of a vehicle, it disrupts the smooth flow of air, leading to increased drag and, consequently, higher resistance. In contrast, positioning the box behind the car allows for more streamlined airflow, minimizing turbulence and optimizing aerodynamic efficiency. This configuration enables the vehicle to traverse through the air with reduced resistance, ultimately resulting in improved performance and energy utilization.

So.. does it really make a difference on my trip?

The implications of these findings extend beyond mere numerical disparities. In practical terms, optimizing aerodynamics by placing the storage box behind the car translates into tangible benefits, especially for electric vehicles. For instance, for an internal combustion engine vehicle with a 60-liter fuel tank and a consumption rate of 6.5 liters per 100 kilometers, the aerodynamic improvement could save approximately 0.39 liters of fuel per hour of driving. Similarly, for an electric car like the Tesla Model 3, which has a battery capacity of around 75 kWh and consumes approximately 15 kWh per 100 kilometers, the aerodynamic enhancement could lead to an increased range of approximately 7.5 kilometers per hour of driving, resulting in an almost 40 km longer drive before having to recharge. By embracing such aerodynamic enhancements, automotive manufacturers can unlock greater sustainability and efficiency in their vehicles, aligning with the imperative of advancing towards a greener automotive future.