Understanding Aerodynamic Drag and Its Impact on Your Truck

With the typical semi-truck averaging just 6 miles per gallon (mpg), it is important to look for ways to improve fuel efficiency in any way possible. Aerodynamics can play a role in this. Making it easier for the truck to move against the force of air can help to reduce the amount of fuel needed to propel the truck forward. Equally important are the quality and condition of the commercial tires installed on your semi-truck and trailer. 

Let’s take a closer look at how all this works.

What Are the Areas of a Truck Where Aerodynamics Matter?

While the overall design of the vehicle matters, there are four specific areas most impacted by aerodynamics:

• The front of the tractor
• The gap between the trailer and the tractor
• The sides and the underbody of the trailer 
• The back of the trailer 

There are two key types of aerodynamic drag: 

1. skin friction drag 
2. pressure drag

Pressure drag occurs as air particles are compressed at the front of the vehicle and then spread out at the rear of it. It occurs as layers of air move away from the surface and create turbulent flow. Skin friction occurs when air particles in the layer nearest the surface collide with the surface of the truck, causing it to slow down. This has a minimal effect on the truck, but it can worsen in colder temperatures.

How to Improve Aerodynamic Drag

There are generally a few ways to improve the aerodynamics of the vehicle to help improve overall efficiency. Here are some recommendations:

• Reduce the gap: Reducing the gap between the tractor and the trailer can help as this makes up about a quarter of all drag. The larger this is, the more fuel you typically burn because there’s more friction.
• Trailer skirts: These are placed under the trailer between the axles. When in place, they work to redirect the airflow, which eliminates the drag from the undercarriage itself. With less strain on the vehicle’s drivetrain, it can operate more efficiently, especially at higher speeds. 
• Mud flaps: The use of mud flaps can also contribute if they are designed aerodynamically. This can help make driving safer on the road with less material flying up from the commercial tires, while also improving fuel efficiency. 
• Trailer tail: Large box-shaped vehicles (such as trailers) provide poor aerodynamics, but newer technology in trailer tails can create a more efficient shape for the trailer. They help redirect the airflow of the rear drag. This can also help to boost fuel efficiency.

A few additional solutions to consider include the use of roof fairings, side fairings, and air dams. Some trucks may benefit from vortex generators and nose cones. Also, consider the impact of your commercial tires. If they are not in good condition, the roll resistance is too high. That means the truck needs more pressure to move against the air.

Update Your Trailer with a Bit of Help

STTC offers 24/7 emergency road service as well as commercial tire service. If you need guidance on trailer repair that could improve fuel efficiency, contact us. Give us a call now at 610-954-8473 or contact us online.