For the 50,000 members of the Iron Butt Association--also known as the "World's Toughest Motorcyclists"--long-distance motorcycling is not a pastime but an obsession. These men and women push the limits of human endurance, often in rides of more than one thousand miles a day. Perhaps the most determined of them is John Ryan, a diabetic and a man who even in late middle age loves nothing better than riding impossible distances at no small risk to himself...