International Truck and Engine Corporation is questioning competitor Freightliner’s recent claim that its new Cascadia is more aerodynamic than other Class 8 commercial vehicles.
“No truck that we have tested has outperformed our new ProStarM in testing to Society of Automotive Engineers (SAE) standards, which include the whole trailer as well as the tractor in real-word simulations,” said Steve Gilligan, asst. gm of International’s Heavy Vehicle Center. “Freightliner simply cannot say that.” Gilligan said the Cascadia in question was tested in Freightliner’s private facility “which cannot accommodate a full tractor-trailer.”
According to Bob Weber, International’s chief engineer of heavy vehicles, the difference between the testing methods is critical. “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,” said Weber.
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,” said Weber. “A vehicle’s wake changes shape and becomes more pronounced as cross winds (and subsequent yaw angles) increase.
“International’s ProStar is uniquely designed to minimize this wake and to achieve outstanding aerodynamic performance across the wind spectrum that drivers encounter every day on the road,” continued Weber. “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).”
Gilligan said International is “looking forward” to delivery of a Cascadia ordered to conduct testing according to recommended SAE standards. He said International’s objective is “to test all competitive products in a simulated real-world environment that removes factors that could distort the aerodynamic results.”
According to Gilligan, International stands by results of previous tests that demonstrated its ProStar to be more aerodynamic than any other Class 8 truck being operated in North America.
International said it 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, said International, and at least one tested as much as 14% less aerodynamic
International acknowledges 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,” Gilligan said. He added that ARC uses full trailers when it conducts its own 1/8th scale wind-tunnel testing of tractor-trailer combinations in its own facilities.
“When the Cascadia package becomes available, International will support independent third-party fuel-economy testing of the Cascadia compared with the ProStar,” according to Gilligan, and these results will be published.
