What makes ahit? Before arecord gets released into the wild, it’s impossible to tell just how it might perform. Producers, promoters and even the musicians themselves routinely fail to predict abestseller, or place high hopes in a track that goes nowhere. In these digital times, B-sides may be athing of the past, but back in the golden age, choosing the right combination proved an imperfect science. With hindsight, it’s astonishing how many stellar tracks were consigned to playing second fiddle. With this in mind, here’s 20 of the greatest rock’n’roll flipsides of all time.