burnthesheep wrote:
How was the tradition arrived at? Desired DNF rate? Enough for a challenge?
What is the DNF rate for full IM? I'm pretty sure some "challenge" fondos even have a higher DNF rate than 5%. I saw 800ish entrants for AOMM and only 408 finishers? I think maybe about 600 or so probably did AOMM vs. Marion. Not sure they list starters together for those. Either way, that's way way higher than 5% DNF rate.
You'd think IM would have a target time such that the DNF rate would be about 25% or so.
No, I don't agree that IM should target a 25% DNF rate. If you want that level of difficulty then you should be doing the XTri series (Norseman, Celtman, Swissman, etc.) instead of Ironman. Or you should be seeking out the very hardest Ironman courses (e.g., Wales and Lanzarote). And you don't get 25% DNF at the toughest races because of advance self-selection. E.g., if you know you are barely going to make 17 hours on the flattest course, you aren't going to pick an IM with over 6,000 ft of net gain on the bike.
As to the reason behind different finishing times, I think it varies race to race. For IM Germany, I believe the 15 hours cut-off is related to the logistics of having a major city (Frankfurt) open for business the next morning. To clean up everything as if the race had never even been there cannot be done with a 17 hour cut-off. Local customs and noise ordinances may have a play in the cut-offs as well (e.g., Ironman Kalmar, Sweden is 16 hours). Having raced many IMs in both the U.S. and Europe, I would say the latter has far fewer one-n-done, barely gonna finish type participants as in the U.S. So I would speculate that many of the RDs there have found that there aren't enough participants coming in after 16 hours to justify keeping the finish line open another hour.