SAE Fuel Economy Tests Reveal Aero Device Performance

September 19, 2013

By Jim Park

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Tests show trailers with side skirts consumed almost 7% less fuel than trailer without skirts
Tests show trailers with side skirts consumed almost 7% less fuel than trailer without skirts

FPInnovations’ Performance Innovation Transport Group has released results of fuel economy testing conducted with trailer side skirt and undercarriage aerodynamic technologies. Results show the side skirts as a group outperformed the undercarriage devices by a significant margin.

The test results show that trailers with side skirts consumed an average of 6.69% less fuel than similar vehicles without skirts. Trailers with undercarriage aerodynamic devices consumed 1.43% less fuel on average than similar units without the deflectors.

“The goal of these trials was to identify the real value of each technology so fleet operators can focus their implementation efforts where they get the best value and can more easily justify their capital investment,” said Yves Provencher, director of PIT. “Our controlled test-track fuel efficiency studies accelerate technology implementation and provide the commercial vehicle industry with the information it needs to make sound technology choices.”

Trailers with undercarriage devices consumed almost 1.5% less fuel than trailer without deflectors.
Trailers with undercarriage devices consumed almost 1.5% less fuel than trailer without deflectors.

PIT's trailer aerodynamic device tests were performed at the Transport Canada Motor Vehicle Test Centre in Blainville, Quebec in accordance with SAE J1321 Fuel Consumption Test Procedure - Type II. For each test, unmodified control vehicles and test vehicles had the same general configuration, and were coupled to the same trailers for base and test segments. Vehicle load weights were maintained throughout the test. All vehicles were in good working condition and set to manufacturer's specifications.

Fuel consumption for the tests was measured by weighing portable tanks before and after each trip. The testing consisted of a baseline segment using non-modified vehicles followed by a segment using the control vehicle and test units equipped with the aerodynamic devices. For baseline and final segments, results were presented as the ratio between the average fuel consumed by the test vehicle and the average fuel consumed by the control vehicle. The values for fuel savings reflect the changes resulting from the modification of test vehicles.

For the fuel economy evaluations, PIT tested side skirts from Freight Wing, Laydon Composites, Ridge Corporation and Transtex Composite. Fuel savings with these devices ranged from 5.2% to 7.45% compared to similar vehicles without skirts.

Trailer undercarriage air deflectors tested by PIT were supplied by AirFlow Deflector, Airman and SmartTruck. Fuel savings measured on vehicles equipped with the devices ranged from 0% to 2.2%.

"There's a lot of confusion in the industry about the skirts and undercarriage technologies, so we want to try to clarify the issue," says Provencher. "In the case of these test, the results were collected over a period of five years. The various vendors paid for the tests, signed a contract acknowledging that the results could be published by PIT. That's helps us maintain our independence and impartiality."

Fleets that are approached by vendors with a product are referred to PIT to have the product tested before the fleets will even look at it. It's like the "Gold Seal" of approval, Provencher says.

"The vendors know there's not much point in knocking on the fleet's doors until they have some credible test results in hand," he says. "The vendor pays for the test, with typically costs about $18,000. If they get positive results, they can take them to the fleet, to SmartWay, where ever they want."

User Driven Testing

PIT operates a testing consortium with about 50 fleet members that each pay a membership fee to be part of the group. Fleet members range from that largest and most innovative fleets in Canada to one small Quebec-based fleet of 25 trucks. There are just two American fleets in the group. Fees are based on fleet size, and vary from $35 to $50 per truck per year. The minimum fee is $5,200.

"There's a networking effect to this as well," Provencher notes. "It's not just about the results of a particular test, but it's a chance for smaller fleets to rub shoulders with industry leaders like Transport Robert, SLH and others. If I'm a small fleet, it's a real advantage to sit at the same table with the big guys and discuss fuel saving strategies and testing. There's a lot of value in that."

In the past, PIT, through its Energotest program, has tested low-rolling resistance tires, various tractor and trailer aerodynamic fitments, 6x2 tractor, automated vs. manual transmission, add-on fuel saving technologies and more. PIT has also compared results of the various generations of EPA emissions requirements.

Euro Versus NAFTA

The next results to be released by PIT will be a fuel economy challenge between a typical North American conventional truck with a typical European COE design. The European trucks were delivered to North America this week and were modified to make them compliant with North American electrical standards, brakes, and other small ways. It will be a head-to-head comparison of Euro 5 emissions standards and the current generation of EPA 10 standards.

The project came to life about a year ago at the Hanover truck show, where fuel economy numbers were just too great to ignore. Canadian fleet execs that traveled to Hanover with Provencher were stunned by the numbers, and asked why European technology was not available in North America.

"The thinking was, even if the European emission are a little higher, they still consume 20% less fuel," says Provencher. "That would be a huge benefit to our fleets. We managed to convince Volvo Trucks to get us two trucks to test along with several government agencies to let the trucks into Canada for testing."

They will be compared in standard SAE Type II tests using control and test truck, weighed fuel tanks, etc.

The results will be announced at the 2013 ATA Management Conference & Exhibition in October.


  1. 1. steve gilbert [ September 20, 2013 @ 04:39AM ]

    I pull trailers with side skirts and trailers without.
    Only thing that changes my mileage is weight speed
    and directions of wind

  2. 2. Louie Pfrqangle [ September 20, 2013 @ 07:22AM ]

    What happens when you have heavy, ,wet accumulation of snow and freezing conditions? How do these devises work when you have Elk Mountain, Wyoming winds?

  3. 3. Alan Goodhall [ September 20, 2013 @ 08:02AM ]

    Is there data available on the effects of crosswinds on trailers equipped with side skirts against a conventionally spec'd trailer?
    Every week I pull an empty from Winnipeg down into the Dakotas to reload. It's more than just a little uncomfortable pulling that empty in prairie crosswinds on winter roads when equipped with side skirts.
    Thoughts on this?

  4. 4. German Trucker [ September 20, 2013 @ 08:08AM ]

    SAE J1321 Fuel Consumption Test is not the best test. Skirts will get 6%. The Smart Truck full system will get you 10.5% and a Trailer Tail will get you around 6%. But throw the SAE J1321 test away. It is worthless.

  5. 5. Pauly [ September 20, 2013 @ 08:18AM ]

    The SAE test is garbage. So I lend no credibility to this test.

  6. 6. Jake Osbourne [ September 20, 2013 @ 08:33AM ]

    The company behind this test owns a skirt company. Keep that in mind then draw your own opinion.

  7. 7. Jim Park [ September 20, 2013 @ 09:45AM ]

    In response to a couple of the above comments.
    The crosswind concern is a valid one. I'm going to speak to the testing company about how they account for a steady crosswind in their testing. Thanks for the heads up on that one.
    As for SAE J1321 not be a good test, what would you suggest in its stead.
    And as for the comment about the testing firm, FPInnovations Performance Innovation Transport Group (PIT) has no ties to any product manufacturers. They do not own a trailer skirt company, nor any other aerodynamic fitment product. The vendors pay for these tests, and as I explained in the story, they agree to the publication of the test results.
    Hope that clarifies a few things. Jim Park

  8. 8. Dirk van der Spek [ September 22, 2013 @ 12:54PM ]

    I wonder why testing euro 5 engines. Those are outdated in Europa already since they are selling now Euro 6 engines. With even better fuel economy as I understand it.

  9. 9. Eric [ October 04, 2013 @ 11:46PM ]

    Snow will not build up composite or plastic side skirts that has a smooth surface any more than on the side of a smooth body trailer. We have been running these for 5 years without any issues from snow. As for cross winds, the wings actually add stability to the trailer. Best we can figure, the additional surface of the skirts extend below the center of gravity . Best way to describe them is they pull like drop deck trailers... less wobble, but a bit more push from wind. They just won't rock with the wings on though. As for those under trays... they really do nothing. Look at where they are... what do you expect them to do? The fuel gains are from keeping the wind of of the wheels and cross-members. Those things do not do that. And based on test results... they are proven to do nothing.


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