Carriers Say Wheel Covers Cut Fuel Costs by Making Vehicles More Aerodynamic

This story appears in the July 15 print edition of Transport Topics.

While wheel makers said they are having difficulty making their products more aerodynamic, some fleets said they are finding that full wheel covers can help reduce wind resistance — and improve fuel savings.

Generally speaking, truck wheels are not aerodynamically designed, their makers said, because factors such as strength and durability take precedence.

Aerodynamics “is not one feature of the wheel design that we necessarily consider,” said Chris Putz, principal engineer for Maxion Wheels, based in Northville, Mich. “What’s most important to us is the durability and the strength.”

“The wheel acts mostly as a cavity,” Putz said. “That creates drag, and that decreases fuel economy.”

And that’s why covers help.

A wheel cover “helps prevent a pressure differential” between the outside of the tire-wheel assembly and inside the wheel cavity and may prevent air from flowing into the cavity, he said.

Some fleets report they are realizing fuel savings from using wheel covers.

For example, C.R. England Inc., based in Salt Lake City, and Schneider National Inc., in Green Bay, Wis., are using wheel covers manufactured by Deflecktor Wheel Covers, St. Paul, Minn.

C.R. England has installed the covers on the rear wheels of more than 500 tractors and is in the process of installing them on 500 more, Allen Nielsen, the fleet’s director of fuel, said via e-mail. By reducing wind drag, the covers save fuel, he reported.

“Our controlled test showed 0.703% savings” from using the covers, Nielsen wrote. “We hope to see closer to 1% as we watch the trucks in service.”

He also said the return on investment in the wheel covers will be achieved “very quickly, even with 0.5% fuel savings.”

At $60 each, C.R. England bought 4,000 of them a few months ago, said Jeff Benson, a vice president of Deflecktor.

Each cover, made of polyvinyl chloride, weighs close to 2 pounds, according to the manufacturer’s website. Benson said that Freightliner had made the wheel covers standard on its 2014 Cascadia Evolution tractor. C.R. England has not yet installed wheel covers on its trailer wheels.

“We wanted to see how they did as we put them in service on trucks before moving forward with our trailers,” Nielsen wrote.

Schneider National started using the wheel covers on its tractors three years ago after conducting tests using Society of Automotive Engineers protocol. It concluded that the covers saved fuel, a report provided by the carrier shows.

 “At 63 mph, closing off various wheel positions reduces fuel consumption between 0.65% and 1.50%” with a margin for error of plus/minus 1%, the carrier reported. “The best result was achieved when all drive and trailer positions were fitted with wheel covers,” it added.

More tests by Schneider National a year after the first series found the same fuel savings, the report stated. Even though the accuracy of the tests was plus or minus 1%, “the repeated positive results indicate that the use of wheel covers is directionally positive,” the carrier concluded.

Schneider National announced in 2010 that it was installing wheel covers on all of its tractors.

After a similar test, Kuperus Trucking of Jenison, Mich., installed covers on the rear wheels of its 47 tractors and on the wheels of its 126 dry van trailers in May 2012, company owner Myles Kuperus said. The test showed the wheel covers, manufactured by Aero Tech Caps, also based in Jenison, Mich., provided 2.5% fuel savings, Kuperus said.

He also said the covers paid for themselves in a “couple months.”

“They’re holding up very well,” Kuperus added.

Aero Tech Cap’s wheel covers have an unusual design: They are dimpled.

Kuperus said he tried the wheel covers at the request of Brian Kronemeyer, founder of Aero Tech Caps. “The guy’s right in the same industrial park that I am,” Kuperus said. “He was very creative when he made those dimples. Makes them look like golf balls. I think that added to the [fuel] economy.”

Kronemeyer said the dimples were indeed inspired by golf ball design. On the wheel covers, they produce “a flutter effect that reduces drag,” he said.

The covers are made of ABS plastic, which is known for durability and flexibility, Kronemeyer said. They fit within the bead curl on steel wheels, and that helps hold them in place. They also feature solid and hollow rubber bulbs that act much like the seal on the door of a car, which makes them work on aluminum wheels as well as steel ones, he said.

Each cover weighs 34 ounces, Kronemeyer said, adding that a chrome version is in the works.

According to the ATC website, a set of four of the ABS plastic wheel covers retails for $290.

Although wheel makers said they had heard positive anecdotal accounts of the performance of some wheel covers, they said they had done no tests and had no data of their own to make the case that they were aerodynamically beneficial.

Mark Fonte, Maxion’s marketing and sales manager for original equipment truck wheels, said, “It would seem logical that they are effective, [but] the converse to that is you’re adding another component, which adds weight.”

One wheel manufacturer, however, said it was working on ways to make its products more fuel-efficient.

Accuride Corp., in Evansville, Ind., is working with a tractor OEM to develop an aluminum wheel with design features to enhance truck aerodynamics, representatives of the wheel maker said.

The aim of the project is “to reduce drag on the vehicle,” said Timothy Weir, Accuride’s director of public affairs, communications and marketing.

Craig Kessler, Accuride’s director of product and process engineering for wheels, said steel wheels are not aerodynamically designed. Aluminum wheels might offer more potential for improvement of the overall aerodynamics of a truck, which is the aim of the ongoing project Accuride is engaged in with a tractor manufacturer.

But truck wheel makers must meet industry standards “for fit, form or function,” Maxion’s Putz said.

Fonte added that in the overall aerodynamic profile of a truck, wheels are located “inside fenders or fairings,” both of which have more impact on aerodynamics.

Dave Walters, manager of warranty and field service for Alcoa Wheel Products International, said that in the case of duals, “I don’t see how you can ever improve aerodynamics. I guess every little bit helps, but this is not the biggest fish to fry.”

Fleets need to distinguish between results of controlled tests and day-to-day operations, Walters said.

“The driver really dictates the fuel mileage when you get to the real world,” he said, adding that he wondered whether wheel covers could provide the same fuel savings with every single driver, whatever his or her skill level.

Rather than aerodynamics, a main focus for wheel makers continues to be reducing the weight of their products, they said.

A 22.5 inch-by-8.25 inch wheel that Maxion makes using high-strength, low-alloy steel weighs 68 pounds, Putz said.

“There are opportunities to further reduce” that weight, he said. “There are always new materials being invented.”