STURGIS, S.D. — Vrrrooooom. Vrroom, vroom, vroom.Here at the Sturgis Motorcycle Rally, the annual gathering of all things leather, Harley and free as the wind across an open plain, Senator John McCain came to ask for the votes of America’s bikers. “It will be a good day on election day if there are a lot of bikes parked outside polling places,” Mr. McCain said.The rally has been known for its wilder days but it, like its devotees, is getting on in years. .when the senator was finally introduced, they vroomed those engines, tepidly at first and then, with Mr. McCain’s encouragement, in a roar of approval. Mr. McCain’s message was a jumble of policy declarations and sharp slaps at his Democratic rival, Senator Barack Obama of Illinois. Mr. McCain noted that Mr. Obama had drawn tens of thousands to a speech in Berlin last month. “I’ll take the roar of 150 Harleys any day. Any day,” he said, to more roars.