There are workouts where you finish battered and beaten, muscles packed with lactate. And then, there are days when you just go out and ride your bike. Tad Elliott does 70 percent of his training on two wheels, but there’s one workout that he especially relishes: a 68-mile loop near his home town of Durango, Colorado, that he rides with his friend Troy Wells. Unlike some of the more painful sessions one might do on...