Ironman St. George unquestionably remains at the top of
RunTri's Toughest Ironman Course list. How tough is IM StG? Of the more than 1600 who started the race, 300+ did not finish, about an 18% DNF rate. In the end, 1311 ambitious triathletes finished in a remarkably slow (= difficult) average time of 13 hours, 24 minutes.
Also see our
Ironman St. George Bike/Run Correlation Analysis and
RunTri's Toughest IMs.