On a frigid winter evening, after the sun has dipped behind the trees, Tim Butler heads out for a bike ride. Shedding his daytime financial-analyst apparel in favor of cycling garb, he traverses the rainy streets for an hour or two before heading home for the night. His wife, Sue, one of the top cyclists in the world, makes dinner; she took a three-hour bicycle ride earlier in the day and has her suitcases packed in preparation for yet another race over the weekend. Eighteen bicycles, all ...