The principal ownership of Iowa Speedway has transitioned from one Iowa family to another. The Clement family of Newton has purchased the automobile race track’s holding company, U.S. Motorsports Corp., from the Manatts family, Iowa Speedway officials announced Tuesday. Conrad Clement, founder of Cresco-based Featherlite Inc., along with his sons, Tracy and Eric, and his brother, Stan Clement, also from Newton, are the new principal owners. Members of the Manatt family, owners of Manatt’s Inc., a heavy construction company based in Brooklyn, have been the primary investors since the track was built in 2006.