How Do Vehicle Aerodynamics Change Gas Mileage?

Aerodynamics refers to the system of airflow around a car. The smoother it is, the lower the drag, and the less fuel you burn at a specific speed.

How does aerodynamics influence your gas mileage, and can you address it yourself? We've prepared this article to explain how the optimal design of your vehicle can affect the gas mileage you receive.

The Basics of Aerodynamics in Vehicles

It's important to ensure that the vehicle is designed and specified to reduce aerodynamic drag. One of the primary principles of aerodynamics is to maintain airflow attached to the vehicle.

This attachment results in smooth airflow around the vehicle rather than allowing the air to detach, creating powerful turbulent wind. These areas make the air behave as if the vehicle is larger than it actually is, resulting in increased drag and decreased mileage.

The Role of Front Axles

The position of the front axle can also impact aerodynamics. Set back front axles not only enhance loading characteristics but also provide several specific aerodynamic advantages.

As illustrated, a distinct airflow separation is created near the front wheels due to the bumper design. This forms a narrow low-pressure area, allowing engine compartment air to flow through from the front grille.

Enhancements and Skirting

Skirting the undercarriage enhances airflow at the sides of the tractor by reducing turbulence around the front fender, gas tanks, battery box, access steps, and quarter fenders.

Cab-length undercarriage skirts extend to the end of the day cab or sleeper cab, while full-length skirts reach the back tire.

Side Extenders and Trailer Gaps

Side extenders are beneficial for directing airflow past the tractor and trailer.It's important to note that with large trailer gaps, even on vehicles with side extenders, turbulence starts to form as the air flows over and around the tractor, creating disturbance near the end of the trailer.

Side extenders reduce the airflow between the tractor and trailer and are effective even when trailers are not fully flat. Trailer gaps should be minimized while ensuring sufficient swing clearance for the intended route.

Roof Fairings and Air Deflectors

A prolonged roof fairing or air deflector improves aerodynamic efficiency when full flat trailers are used. If a long-haul sleeper towing a dedicated trailer isn't a standard tall van body, aligning the tractor's height to the trailer's for maximum mileage is vital.

Nonetheless, a roof air deflector helps match flatbed and bulk haul trailers with appropriate height tractors. In some refrigerated van trailer applications, it might also be preferable to operate without the roof fairing to allow significant frontal air to reach the cooling unit.

Wheel Aerodynamics

Vehicle and trailer wheels also contribute to detached airflow and increased aerodynamic drag. By using wheel covers on both sets of wheels, you can expect about a 1% increase in mileage.

To become an industry leader in aerodynamics, Global employs various testing methods to understand the real impact of aerodynamic drag under different conditions.

Real-World vs. Lab Testing

The true measure of a vehicle's performance lies in real-world situations, not in a lab. Nonetheless, extensive research determines how Global conducts on-road testing to ensure our vehicles and our competitors' are evaluated under comparable conditions, minimizing variables.

Key Factors Affecting Aerodynamics

The aerodynamics of your vehicle can affect its fuel efficiency.A key metric is the coefficient of drag, a number between 0 and 1, which assesses how air flows around your vehicle as it moves. The lower the coefficient of drag, the more efficiently your vehicle moves through the air.

The coefficient of drag is just one aspect of the aerodynamics equation. Speed, vehicle weight, frontal area, and air density all play roles. As speed decreases, aerodynamics play a smaller part in gas mileage.

If your vehicle is heavier, it might not move as swiftly through the air. The shape and surface area of the vehicle's front can also impact its aerodynamic profile.

As speed increases, aerodynamics become more prominent when calculating gas mileage. Driving at high speeds while towing alters the vehicle's aerodynamics and increases its weight, both of which can reduce fuel efficiency.

Additional Considerations

Aerodynamic drag has various sources.Waxing your vehicle isn't just for aesthetics – skin friction as air passes over a surface is a real phenomenon. While it might not be as impactful as factors like turbulence and pressure differences, it all contributes.

Vehicle manufacturers prioritize improving their vehicles' aerodynamic efficiency because it translates to better gas mileage figures, increased sales, and environmental conservation.

Improving efficiency through aerodynamics is often more cost-effective for manufacturers than investing in weight reduction or advanced engine technologies.

Understanding the Coefficient of Drag (Cd)

Cd represents the coefficient of drag, and it's the number manufacturers use to indicate the efficiency of their vehicles. It measures how "slippery" a vehicle is as it moves through the air.

However, it doesn't convey the total aerodynamic drag a vehicle produces. Frontal area mainly depends on the vehicle class and type, and little can be done about it. For instance, a luxury sedan will inevitably have a larger frontal area than a compact car.

Practical Tips

Regarding air density, driving in a different location or on another day won't change it. As a tip, try pushing a car, and you'll quickly realize that friction and tire rolling resistance consume much energy, especially if you struggle to push the car even at slow speeds.

In conclusion, when planning your driving routine, remember the importance of designing and specifying a vehicle to minimize aerodynamic drag.