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Take off your Skirt?

Updated: Oct 3, 2020

Are trailer skirts worth the expense?

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Now if you drive in California, you’re stuck having to use them. Under the rule, all 53-foot box-type trailers (dry or refrigerated) must be equipped with Environmental Protection Agency SmartWay-approved side skirts or tail fairings that improve fuel economy from 4% to 5%, in addition to low-rolling-resistance tires (either standard or wide-base singles).

A host of exemptions have been rolling in since the rule was implemented that allow different compliance dates for fleets of different sizes engaged in local and regional operations as opposed to strictly long-haul operations.

To be perfectly clear my background is aviation for the last 25 years as a helicopter pilot so I have a pretty good understanding on aerodynamics. Parasitic drag is a common term used in aviation and this device/skirt is exactly what this is. Any item introduced into an airflow will have an effect but will the effect be more of an added value or a deficit to the overall goal.

There are many factors to consider prior to purchasing a skirt kit for your trailer and if the acquisition will yield a return on your investment and how long that will take. At the time of writing this article the price of Diesel Ultra Low Sulfur (15 ppm and Under) is on Avg. $2.43 Nationwide during July 2020.

Let’s say you drive 120,000 miles per year at $2.43 gallon getting 8 miles per gallon you would save 5% on fuel equaling $1,822.50 per year.

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The efficiency of an airfoil doesn’t become effective until a specific airspeed is achieved based on the design of the airfoil. I can correlate this to the blade of a helicopter as it rotates at a high rate of speed with the blade tips nearing 300 mph. In a hover the efficiency of the blade is not great requiring much more power to stay in the air but as the helicopter starts to accelerate passing the magic >13 kts. of airspeed the airfoil becomes much more efficient requiring less power to maintain flight. The same can be said when a truck is traveling less than 55 mph the skirts are not any benefit at all. If most of your driving is around 55 mph or less then do not waste your money on these.

These skirts simply keep the airflow from going under the trailer which causes drag along the underside hitting axles and wheels.

The other issue I see from just an operational standpoint is damage control. Let’s face it your truck will undoubtedly have trailer rash at some point and these skirts will become a casualty.

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I pushed out an enquiry to some drivers regarding this topic to see what they had to say and this was the response I received.

Question for Van & Reefer drivers. Those who are equipped with trailer fairings do you notice much difference in fuel economy? Also, what about driver fatigue running with and without? Please be specific on the type(s) of fairing you have.

· A trailer tail will improve your fuel economy by about 0.5 mpg, and the fairings by about 0.3 mpg. Never had a bit of problem with wind in Wyoming or any other state.

· I have driven with and without it on the trailer it depends on if your running like a bat out of hell or if you’re one that actually uses your cruise control.

· I’m sure somebody will argue about this but my experience is there is a big difference in the fairing and the regular trailer the fairing does catch more air and, in my opinion, gives you a greater chance of rolling over

· I feel that they handle the wind gusts a lot better with fairings

· Look at who ends up in the ditch in Wyoming in the winter, or blown over in Wyoming on dry roads. Trailers with fairings and super single tires, especially on slick roads.

Does a price tag of (US$1300 to $2700) for a set of these skirts make sense for you? Well this is a question only you can answer especially with the low price of diesel at the moment.

Jay Schmidlapp | President


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