ORLANDO. Responding to the release of new fuel economy test data from International Truck and Engine Co., competitor Freightliner LLC said it questions the real-world value of the tests, which showed International’s new ProStar tractor to be 5.7% more fuel efficient than the new Freightliner Cascadia. Back in September, Freightliner released its own test data claiming that its new model was more aerodynamic and therefore inherently more fuel efficient than the ProStar.

The battle over aerodynamic and fuel efficiency for the two new Class 8 tractors has heated up significantly during the American Trucking Assns. annual convention, with both sides releasing new print ads and brochures claiming superiority over the other by name.

Responding to the new International tests in a written statement, Michael Delaney, Freightliner senior vp of marketing, said that based on the company’s own testing, “We find Navistar’s claims of a 5.7% fuel economy advantage to be highly misleading and potentially questionable information for customers making choices for normal, day-to-day operation.”

Specifically, he said that the standardized SAE Type III fuel economy tests run by International were “not structured to be predictive of real-world duty cycles and conditions.”

Instead, the Freightliner vp said, the SAE tests “are typically used to narrow the range of variables in preparation for subsequent and more robust Type IV tests. In our view, it is irresponsible to imply that Type III testing alone would ever be an accurate fuel economy predictor.”

In the release of its test data, International said it planned to conduct SAE Type IV tests with the ProStar and other competitive models early next year. The Type IV tests are run over 1,000 miles on public roads.

Escalating the war of words between the two truck makers, Delaney’s written statement released today at the ATA meeting added: “We are dismayed to see a competitor confusing reckless selling with science in a way that may cast doubt on any OEM-supplied data going forward.”