He can pull 6 Gs. He's been the centerfold for Cycle News and poses regularly for fan photos. He's a survivor of the grueling Baja 500 and has racked up more than 10,000 hours on a dirt bike. Sometimes, you can barely see the 70-pound pooch -- a blue merle Australian shepherd -- through the dust on his goggles and his custom helmet, complete with cam. "I am his biggest fan," said Mike Schelin, Opee's owner, race partner and a purveyor of used motorcycle parts from a shop next to his mobile home. Schelin got the dog in 2001 shortly...