Trailer Talk

Are 2.23% Fuel Savings Too Modest to Sell this Aero Improver? Maybe Not

July 9, 2013

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Tractor AeroKit panels and wheel covers smooth air flow around the tandem. Devices are made of rugged thermoplastic olefin.
Tractor AeroKit panels and wheel covers smooth air flow around the tandem. Devices are made of rugged thermoplastic olefin.

It takes a tractor to move a trailer, which is why we’re looking at this new product from a small company: Tractor AeroKit from Flow Below Aero Inc., in Austin, Texas. The kit saves fuel by smoothing air flow around the vehicle’s drive wheels.
And even though the proven percentage is modest, the product will pay for itself faster than trailer side skirts, the company’s founders assert.
That claim is based on the fact that many trailers spend much of their lives parked at terminals and in customers’ yards, said Mario Bravo, Flow Below’s marketing manager. 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.
An 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.
OK, my skeptical mind immediately said, aside from aerodynamics, what about durability? How do those panels hold up against impacts by road debris, like heavy strips of wired rubber from blown tires, and to sub-zero cold?
Bravo answered that the devices are made of rugged thermoplastic olefin, or TPO, the same material used for OE-style tractor side skirts and Minimizer aftermarket fenders.
“In ‘Tested and Tortured’ ( they drive over it and drop a wrecking ball on it,” Bravo said of a Minimizer promotion. “In ‘Proving Grounds’ ( they use a baseball pitching machine to propel billiard balls at it at 95 mph, and they freeze it with liquid nitrogen and then hit it with sledge hammers.  Our product is made out of the same material.”
Fine. But is it wise to criticize trailer skirts? Bravo and his colleague, Kyle Walker, insisted that they are not knocking trailer skirts or other aero products, just pointing out the reality that trailers are parked so much.
Well, what exactly are the savings you saw in testing? I asked Bravo.
“We have internally debated whether or not to publish our percentage fuel savings test results,” he replied in a thoughtful e-mail message. “That is because there are a lot of exaggerated claims from manufacturers of fuel-saving products. I know of no other product on the market that makes a percentage fuel savings claim that represents a realistic number that will be achieved on average on the road.
“Because of the prevalence of exaggerated fuel savings claims in this industry, we have been told by fleet owners that they usually look at manufacturers' claims and cut the number in half to get an idea of what they will actually achieve on the road. You can see the problem that this presents to us if we are already reporting the number that they will actually achieve on the road while competing aerodyanmics products are reporting exaggerated fuels savings.

“When the Texas A&M Transportation Institute tested our product, they also tested a popular trailer side skirt that claims in excess of 6% fuel savings,” Bravo continued. “Our product tested at 2.23% fuel savings while the trailer skirts tested at 3.66% fuel savings. Our product tested at 60% of the fuel savings that the trailer skirts did.
“However, you can see how 2.23% fuel savings can be dismissed by a potential customer as insignificant when compared in his head to 5% to 7.5% fuel savings claims by trailer skirt manufacturers. Our 2.23% fuel savings translates to around $1,800 a year in fuel saved when driving 125,000 miles with diesel prices of $3.90/gallon.”
At that rate, the payback for a Tractor AeroKit is nine months, says the company’s website, The device is also quick to install – about an hour by one man – and it weighs 75 pounds, half or less what a set of trailer skirts weigh.

“If a fleet owner with limited capital is considering either trailer skirts or a Tractor AeroKit, the Tractor AeroKit becomes very competitive when a fleet has more than two trailers per tractor,” Bravo said.  “That is because the fleet owner has to buy twice as many trailer skirts as Tractor AeroKits” to completely equip his trailer fleet. “And you are getting a return on your investment every time that tractor is on the road at highway speeds.  This makes for a faster payback on a fleet owner's investment.

“We believe that there are many possible reasons for the discrepancies between the SAE J1321 Type II protocol test results that Texas A&M Transportation Institute found and the numbers that trailer skirt manufacturers claim. Testing under higher wind conditions will improve the effects of aerodynamic products.
“The SAE J1321 Type II protocol allows for testing in wind conditions that average under 12 mph. Our tests were conducted at an average (wind speed) of under 3 mph. If we were to wait around for winds that approach an average of 12 mph, we would be able to truthfully report test results that are significantly higher, yet not representative of what truck drivers would see on the road on average.

“In addition, wheel cover manufacturers claim fuel savings of up to 3%. We have not seen fuel savings test results for wheel covers alone that are above the margin of error of the test.
“Texas A&M Transportation Institute test results that we have seen show that wheel covers only achieve significant savings when used as part of a system with either our Tractor AeroKit or with trailer skirts.  Again, it puts us in an awkward position to advertise a smaller fuel savings test result for our entire Tractor AeroKit then what is being claimed by other manufacturers for wheel covers alone.”
If you’ve read this far, you might not be typical of a lot of truckers whom Bravo and Walker have heard from. It’s simply a lot of information for people to digest.
“The problem that this poses for us is that people tend to already think they know the answer to what they are looking for,” Bravo lamented. “They read until they see something that they misinterpret as supporting what they believe, and then move on.  I have to delete posts on our FaceBook page every day from owner-operators who make claims about fuel savings that are not based in reality, such as, ‘Aerodynamics don't work at speeds over 64 mph.’"

That brings us back to that unadvertised 2.23% figure.
“If we give them enough information to get them interested, but leave them wanting more information, then they will be more inclined to contact us, at which point we can begin a conversation and clarify any misconceptions they may have.  That has been our strategy, anyway, based on the challenge of trying to remain honest in advertising.
“Who is to say if our product is the best? We are just trying to avoid the old adage of ‘good guys finish last’ and hope that over time we will gain a reputation for our honesty and reliability.”


  1. 1. Bruce Janzen [ July 12, 2013 @ 03:17PM ]

    The difference between the tractor flow devices and the trailer skirts is California recognizes them as meeting their criteria for fuel savings and the Flow Below kit doesn't. Since many fleets are needing to become California compliant the skirts are the logical choice if given the option. At some point aesthetics become part of my decision making process and my opinion is the wheel covers and tractor wheel fairings are just plain ugly!

  2. 2. Mike Bulriss jr [ July 14, 2013 @ 08:49PM ]

    I have heard that the trailer skirts actually can seriously decrease fuel mileage and handling when going north/south because of side winds.

  3. 3. Mario Bravo [ July 16, 2013 @ 11:41AM ]

    Bruce, FlowBelow does meet all of the EPA SmartWay test requirements demonstrating fuel savings. However, the EPA does not have a category for products that go on the truck as of yet. They only have a category for products that go on the trailer. We are talking with them now about expanding their criteria or adding a category.

    As far as asthetics go, our AeroKit will be available in chrome in just three weeks for those that don't like the blackout look.

  4. 4. Charles killian [ July 22, 2015 @ 09:30PM ]

    See setting up account with you. Ok

  5. 5. D [ April 22, 2017 @ 10:10AM ]

    This system is crap and useless. 1st and foremost, it's an inconvenience. Gotta take the damn hib caps off gor a pre trip, and the damn ferrings get in the way to pull the release handle for the 5th wheel. I shouldn't need extras to pull the 5tu wheel release nor should i have crap making me spend extra time pre tripping.

  6. 6. Brandon Minick [ December 20, 2017 @ 10:50AM ]

    I have 3 sets of these flow below kits and I have 6 tractors, all same exact spec. I can tell u for sure, the lifetime average is better on the flow below tractors. I also have the opinion they look nice! I don't understand why people, mainly owner operators resist and write-off things that put money in their pockets ! I don't get y anyone in their right mind would buy a 379 or w900 in this day in age! Cool is not always cool. I'm gonna take my fuel savings and buy a new zl1 1le! #goflowbelow!


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Author Bio

Tom Berg

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Senior Contributing Editor

Journalist since 1965, truck writer and editor since 1978. CDL-qualified; conducts road tests on new heavy-, medium- and light-duty tractors and trucks. Specializes in vocational and hybrid vehicles.


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