WARRENVILLE, Ill — Freightliner’s chief rival in the commercial class 8 market is questioning its competitor’s recent claim that its new Cascadia highway tractor is “officially” more aerodynamic than other heavy truck in its class.

“No truck that we have tested has outperformed our new ProStar in testing to Society of Automotive Engineers (SAE) standards, which include the whole trailer as well as the tractor in real-word simulations,” says Steve Gilligan, assistant general manager of International Truck & Engine’s Heavy Vehicle Center. “Freightliner simply cannot say that.

“The Cascadia was tested in Freightliner’s private facility, which cannot accommodate a full tractor trailer.”

The difference between the testing methods is critical, according to Bob Weber, International’s chief engineer of heavy vehicles. “Since their test does not include the aft section of the trailer, it does not allow a wake to form behind the vehicle as it does on the road,” he says.

Straight as an Aero? International claims no
truck trumps the ProStar in aerodynamic tests.

Both the aft end of the trailer and the size and shape of the wake behind the vehicle “have a profound influence on the overall aerodynamic drag of the tractor-trailer combination,” he continued. “A vehicle’s wake changes shape and becomes more pronounced as cross winds (and subsequent yaw angles) increase.

“It does not appear that Freightliner is presenting aerodynamic drag data based on the wind-averaged drag coefficient formulation recommended in the SAE best practice for truck and bus wind-tunnel testing (SAE J1252).”

Researchers for Freightliner measured wind drag on the front, sides and back of the tractor, as well as the front of the trailer. According to Freightliner, The ProStar recorded 7.8 percent more drag than the Cascadia; the 780 showed 9.6 percent more drag; the T660 showed 18.8 percent more drag; and the 386 showed 22.9 percent more drag.

Gilligan said International is looking forward to delivery of a Cascadia, ordered to conduct testing according to recommended SAE standards. However, these plans have been postponed due to an apparent delay in shipping. Citing communication from a Frightliner dealer, Gilligan explained that Cascadias are being held for shipment because of production issues.

Additionally, chassis skirts apparently will not be available until late in the year, which will impact testing of full aerodynamic specifications.

International says its goal is to test all competitive products in a simulated real-world environment that removes factors that could distort the aerodynamic results.

The company stands by results of previous tests that demonstrated ProStar to be more aerodynamic than any other Class 8 truck being operated in North America.

International has spent more than $1 million conducting full-scale tractor-trailer testing to SAE standards at Canada’s National Research Council Institute for Aerospace Research. Competitive Class 8 vehicles including the Freightliner Century, Freightliner Columbia, Peterbilt 386, Volvo VNL780 and the Kenworth T2000 were tested, filmed and the results documented.

“None of these vehicles was more aerodynamic than ProStar, and at least one tested as much as 14 percent less aerodynamic,” the company says.

International says that while Freightliner used a reputable agency, Auto Research Center, Inc., to observe the testing, ARC later stated that it “was not contracted to validate the flow quality of Freightliner’s wind tunnel nor establish the criteria for the these tests.”