Understanding Aerodynamic Drag and How It Impacts Your Truck

Apr
26

Posted On Apr 26, 2018

How much do you know about semi truck aerodynamics? If you have a truck fleet, it is very important that you understand the relationship between truck aerodynamics and fuel efficiency. Put simply, aerodynamic drag is a force on your truck that requires your truck to use energy to overcome it. That energy means unnecessary fuel use for your tractor trailer. Aerodynamic devices that promote tractor trailer aerodynamic drag reduction, then, can provide greater fuel efficiency for your trucks.

What Is Aerodynamic Drag?

Aerodynamic drag is a mechanical force generated by the movement of the truck through the air as it accelerates forward. It can be thought of as air resistance. Essentially, it is an opposing force that your truck needs to overcome in order to move forward. The stronger the effects of drag, the more energy the truck requires to move at the desired speed.

How Does Aerodynamic Drag Impact Your Truck?

There are two types of aerodynamic drag your truck experiences: pressure drag and skin friction drag. Pressure drag is the result of air particles that are compressed in the front of the truck and spread out in the rear. This happens when layers of air swirl away from the surface and create a phenomenon called turbulent flow. Since there is more pressure on the front than the back, drag occurs.

Skin friction drag is a result of air particles in the layer nearest the surface of the truck colliding with the surface of the truck and slowing it down.

The effect of skin friction drag on tractor trailers is minimal. However, because these trucks are so heavy and large, and because it is difficult to aerodynamically shape a truck, pressure drag is a major problem. If you operate in cold conditions, the air is denser and aerodynamic drag is magnified even further.

The amount of work a truck must do to reduce drag creates a serious drain on fuel efficiency. The faster a truck goes, the greater the effect. The U.S. Department of Energy (“Technology Roadmap for the 21st Century Truck Program: A Government-Industry Research Partnership.” Technical Report 21CT-001, December 2000) found that 85 percent of the useful energy produced by your truck engine is energy used to overcome aerodynamic drag and rolling resistance. Additionally, 85 percent of the useful energy produced by the engine is used to overcome aerodynamic losses and rolling resistance. Clearly, if you manage a fleet of trucks, aerodynamic drag is a big issue that it is in your interest to address.

What Can You Do About Aerodynamic Drag?

So what can you do about aerodynamic drag for your trucks? Well-balanced, low-rolling resistance tires that are properly inflated are always a good idea for fuel efficiency. If it were feasible, the best approach would be to redesign all of your trucks with an aerodynamic shape, but the nature of truck work tends to conflict with the requirements of aerodynamically-shaped vehicles, in addition to the fact that it would be cost-prohibitive. So what is the solution?

A common solution is to add features to your truck to give it aerodynamic properties. Fairings are the most popular features of this type. Types of fairings include roof fairings, side fairings, underbody fairings and end or tail fairings. Other aerodynamic additions to trucks include air dams, vortex generators, gap reducers and nose cones.

All of these features are designed to turn your boxy, bulky truck from an object that fights wind into an object that “goes with the flow.” These additions change the shape of your truck so air flows over and around it rather than flowing into it or clinging to its surface. The result can be massive energy savings to the tune of hundreds of gallons of fuel a year. In fact, according to FleetOwner.com, using the right features to make your combination truck 15 percent more aerodynamic can save you 2,430 gallons annually per truck. You can do the math on how much money that could save your company each year.

Adding features like underbody fairings, tail fairings, and side skirts will require a time and money investment. But if you have multiple heavy trucks whose speed frequently exceeds 60 miles an hour, you will almost certainly find that the investment will pay for itself in fuel savings extremely quickly. If you’re not convinced yet, you can always try upgrading a quarter of your fleet with aerodynamic features to see how much money you save in fuel before moving on to the rest of your fleet.

Other Fuel Efficiency Tips

In addition to the effects of the forces of drag, you can lose a lot of fuel efficiency by not taking proper care of your truck tires. For over 40 years, IMI Products has been delivering tire and wheel products to extend the life of your tires, reduce vibration and improve fuel economy. Products include our STS Sealant — the highest-performance sealant for heavy-duty and commercial vehicle tires — and our famous EQUAL FLEXXTM wheel-end solution with Dual Force Active Balancing technology for reduced wear, lower vibration, lower rolling resistance, and a smoother ride.

If your business depends on trucks, your business depends on tires. For more information about reducing aerodynamic drag, increasing fuel efficiency and taking better care of your trucks with great wheel and tire products from IMI, call us at 1-800-233-7086 or contact us online today.

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Fuel Efficiency

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