Navigate to the race's athlete guide - even the one from the previous year. It will list all intermediate cut off times.

That's just for that single race. If you read my post, it's asking for a single side by side location for all races with their cut off times. I know it is listed for the individual races in the race guides. Looking for more of a "global location" list. It'd be just an interesting read I think, that's all.

I don't think there is a global list.

I only discovered Ironman Asia Pacific (Cairns) was a 16:30 finish cut off this past weekend.

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17 hours is the tradition in North America and the UK, but most IMs in continental Europe have cutoffs under 17 hours. You would have to look at all the Athlete Guides one by one to get them. However, the cut-off times are typically based on other factors than course difficulty. E.g., IM Germany is only 15 hours but is much, much harder than IM Barcelona which is 15 hrs 40 mins. Ironman Norway is 16 hrs 30 mins. But to muck up the theory IM Austria is a full 17 hours. :)

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.

I think the "tradition" was simply that the Hawaii race started at 7am and the finish cutoff was midnight, therefore 17hrs.

Most IMs end up with around a 15-20% DNF rate assuming conditions are relatively nominal. When bad weather hits, or whatever, the DNF rate jumps.

Sure, but would you be willing to pay 15-20% more to race? Because a lot of those 25% would not even bother signing up.

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Chattanooga was shortened due to the start time. Originally they had planned for a midnight finish, but since the sun was not up yet at 7AM, it was unsafe for the swim to start in the dark.

I believe there are some insurance and permitting issues you can get into when you cross the 12:00 hour, since the race is on XX day, after midnight it is now the next day

I'm willing to bet the cut off time has absolutely nothing to do with the finish rate, but rather individual race particulars. Could be sunrise, sunset (everyone off the bike) or any number of other factors.

20% isn't entirely true......

https://www.runtri.com/...onman-dnf-rates.html

I think the "tradition" was simply that the Hawaii race started at 7am and the finish cutoff was midnight, therefore 17hrs.

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I wish I could find the photo from like the 1st few years of Hawaii from some old dude still running the marathon the next day reading the newspaper about the race and race winner. IE- reading about the very race he's still in. Of course this was very early when there were essentially no rules, it was just get to the finish however and whenever you could.

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Brooks Doughtie, M.S.
Exercise Physiology
-USAT Level II

Thanks to all for the response. Seems like an interesting data/global list to have, for those wishing to look at races they would have a better chance of finishing. I know some who are barely doing 17 on a flat course may want to reference a list like that, if it did by chance, have anything to do with difficulty of the course. You wouldn't do a Penticton or St. George race if you're going 16:45 or just under 17, on a flat course of say, Ironman Florida. I'd advise someone in that position to just not even sign up for those & look more towards a 16:30 cut off time race--then just figure out where to take back that 15 minutes or whatever.

Realizing too, some may be older & that is all they have in them, but things like conditions can play a big part (wind, rain). It was just a thought. I know someone who did 16:45 at Ironman Boulder & then turned around & signed up for St. George next year--and I was like...WTH?? Seriously? Okay...good luck with that, you have some work to do!

90% of what you are asking for already exists: https://www.trirating.com/course-ratings/