WASHINGTON (April 2)—The National Highway Traffic Safety Administration has closed its investigation into 2.7 million General Ameri*550 tires produced by Continental Tire North America Inc. NHTSA started its probe in July after the Ameri*550 was one of the tires that were the subject of a study by the House Energy and Commerce Committee. The panel said the General-brand tire—one of the tires being used as a replacement for the recalled Firestone Wilderness AT tires—had a higher rate of claims than the Firestone tires they were replacing. NHTSA ended the probe into the Ameri*550 tires because its investigation found no safety-related defect. The agency also said it found no reports of fatal accidents related to the Ameri*550. NHTSA looked into all Ameri*550 tires made since 1995, 85 percent of which were supplied as original equipment for the Ford F-150 pickup.