Worth It or Not? The Aerodynamics Debate

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They’re ugly. They don’t make enough difference in fuel economy to be worth it. They won’t hold up to road abuse. They don’t produce the savings I can get just by slowing down.

Drivers and fleets have plenty of reasons they’ve generally opted out of aerodynamic add-ons, and while it’s true they’re not smart for everybody, companies are getting better at making durable, effective drag reducers. If you’ve always written the things off, it might be time to re-investigate.

Henry Albert, a trucker since 1983 and a contributor to TeamRunSmart.com, drives a 2013 Cascadia Evolution and has been on a pretty well-publicized quest to achieve 10 mpg for over five years. In a recent interview, he says he’s achieved in excess of 10 mpg on many individual driving days. His truck is completely decked out, with side skirts, nose cone, a trailer tail and wheel covers.

“I have drivers tell me all the time, ‘side skirts don’t make that much difference,’ and they’re right – they only save between 2.5% and 3% in fuel cost. But they also say the same thing about the nose cone and the wheel covers and trailer tail, but cumulatively, when I put it all together, it adds up,” Albert says. The fuel savings of adding aerodynamic modifications to his truck covered his cost in six months.

On the other side of the debate are drivers who point to the weight of the add-ons and the fact that on certain routes, crosswinds in combination with accessories like trailer side skirts can actually create drag. In the comments section of this article, a driver who travels the I-80 corridor between Milwaukee and San Francisco, a route where he’s usually rolling through 25 mph crosswinds, installed side skirts. He reports no difference in fuel mileage and concludes, “There is only one way to good fuel mileage, and that is SLOW DOWN. I went from driving the 75 mph zones to driving 60 and have saved an average of 160 gallons per trip.”

But this driver begs to differ: “I don’t subscribe to the theory that slowing down increases profits!” In the comments section of an article on the trailer Kevin Rutherford developed for owner-operators, he explains that, “when you slow down, your are also reducing your per-hour revenue.” By way of example he says that a driver averaging 70 mph and earning $2 per mile grosses $140 per hour, while someone driving an average of 60 mph at that same pay rate makes $120. Since fuel only costs $11 per hour more to run at 70 mph, the 70 mph driver is $9 per hour more profitable. His philosophy: “Revenue first, then control costs.”

One way he controls his costs is by employing an undercarriage device and nose cone to diminish aerodynamic drag. He uses an Airman undercarriage add-on, which is designed to move with the tandems, unlike the skirts that are stationary. He says, “For every slider hole you move the skirts away from the tandems, your efficiency decreases. At a certain distance, the efficiency is actually worse than no skirts at all. The 5-6% fuel savings I’m getting from skirts is only achieved at the 40-foot California setting. Utilizing both the nose cone and Airman, I am achieving 7.2-7.4 mpg running @ 75 mph in 75 to 80 mph states, usually grossing 75-80,000 lbs and am hitting 11 mpg empty.”

An option for drivers who determine trailer side skirts aren’t right for their situation are tractor wheel covers. As Mario Bravo, marketing manager for Flow Below points out in this article, one advantage of making a modification to the tractor is that you get that fuel economy benefit even when the trailer is sitting in a customer’s yard, unlike trailer side skirts. “The higher a fleet’s trailer-to-tractor ratio, the more standing time, and no aerodynamic device saves anything when the vehicle is sitting still,” he says.

His company’s AeroKit consists of panels that close the gaps between a tandem’s drive wheels, and others that guide air as it leaves the tandem area. Circular covers block wheel indentations and reduce turbulence.
The advantage of being an owner-operator vs. a fleet manager in this situation is that owner-operators many times run dedicated loads and/or routes, according to comments in this article by Mitch Greenberg with SmartTruck Systems.

He points out that they also tend “to measure their fuel mileage more consistently and run the same equipment day in and day out. Any differences that stem from aerodynamic add-on devices will more effectively and directly present themselves, Greenberg says, due to the aforementioned variables being so controlled, which is often not the case for large fleets looking to implement aero devices.”

There’s no one right answer and every driver needs to test for himself what combination of equipment, accessories and driving skills will create the best results.