RIO DE JANEIRO, Aug 13 (Reuters) - Britain and the United States traded world records in the Olympic track cycling women's team pursuit to set up a mouth-watering showdown for gold later on Saturday. Racing in their heat against Australia, the world champion Americans, led by Sarah Hammer, broke the record set by Britain in Thursday's qualifiers by a full second, clocking four minutes 12.282 seconds. They, nor the crowd in the Rio velodrome, had barely taken stock when in the following heat the British quartet, up against Canada, lowered the mark to 4:12.152. ... More...