The average triathlete spend months, if not years, preparing to compete in an Ironman Triathlon, to finish the 2.4 mile swim, 112 mile bike ride and 26.2 mile marathon in less than 17 hours. In a typical North American Ironman, nearly 95% of those who start will ultimately finish the race. And it's interesting to note that even with a world-class field, Kona has a 7% DNF rate.
In 2010, two races deviated from this norm. The Inaugural Ironman St. George was far tougher than expected, leading to a 14% DNF on a very difficult course (we estimate 18% in 2011). In extreme heat, Ironman Louisville Kentucky had 16% DNF, though in previous years, the rate has been in the 5% to 7% range. Also see our DNS/DNF Analysis and the RunTri.com Challenge Index: Top 25 Toughest Ironman Triathlons.