Wind tunnel testing on Freightliner's Cascadia may not have delivered accurate results, International officials contend.
WARRENVILLE, Ill. — International Truck and Engine has issued a release stating the company does not agree with recent findings by Freightliner which show its Cascadia highway tractor is more aerodynamic than Internationals ProStar.
Freightliner recently released findings of an independent wind tunnel test that showed the new Cascadia is more aerodynamic than its rivals. However, International officials said the testing was not done on a full trailer and is misleading.
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. Freightliner simply cannot say that, said Steve Gilligan, assistant general manager of Internationals Heavy Vehicle Center.
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, added Bob Weber, Internationals chief engineer of heavy vehicles. He added the end of the trailer should be included in testing because it has a profound influence on the overall aerodynamic drag of the tractor-trailer combination.
International engineers say the ProStar was developed specifically to minimize the wake that forms at the aft of the trailer, delivering excellent airflow even when driven through crosswinds.
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), Weber said.
International plans to delve into the issue further, and has placed an order for a Cascadia for testing purposes. In the past, International conducted full-scale tractor-trailer testing at Canadas National Research Council Institute for Aerospace Research in Ottawa. When tested there, the ProStar proved to deliver best-in-class aerodynamics, the company said.
International officials vow to support independent third-party fuel economy testing of the Cascadia compared to the ProStar and the company promises to publish the results when they become available.
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