I think that’s a good rule of thumb. I agree that open marathon is different than IM marathon, but I like to have SOME frame of reference.
As you’ve probably heard…”bike for show, run for dough”. Unfortunately running will be the big determining factor in IM success. “Chi running” on YouTube has some good running fundamentals. If you could get Ryan Flaherty as a guest on the podcast, that would be a really interesting show too.
You can often (roughly) work out your potential IM run time based on your stand alone mara time.
However, something to ponder is, quite often those that come from a cycling background, ride like they are in a bike race, blasting past all us slow 
triathletes. Then they get to the run and they find they have over-cooked things. 15mins faster on the bike can cost you an hour on the run.
Especially if they are a weak runner to start. “I need to bank some time on these fast runners!”.
Then you end up with a run split that’s longer than your bike split 
.
Ever thought about qualifying for Kona via a 70.3? I know someone who qualified at 70.3 Xiamen 30-35 age ~4:22.
Even if this was/is true, it existed basically for marathon runners who decided to take up Ironman as a guide for pacing.
And I believe “the reverse” isn’t true - you don’t need to have ran, or (more importantly) trained for, a 2:45 marathon to be able to run a 3:15 IM marathon.
Im not super confident in my knowledge on the pointy end of the run, so happy to be corrected, but I understand it’s not about having the speed necessary for a 2:45, it’s about having the strength to hold 3:15 after the bike…if that makes sense.
Also, if you check out Coachcox stats for 2019 a 3:30 run has a chance at most IM races, and Gurye, Taiwan and Malaysia had people qualify in M40-44 running much slower than that…4h08 in Taiwan!
If you are thinking about qualifying and serious about this you should research a lot of events and look for the ones that play to your strengths. The window for swimming is 10 minutes, if you can get under the hour then great just keep playing to that strength you are already in the top 10-15% of the field.
Cycling like another poster said, you won’t win the event on the bike but you can lose it. I saw a quote from someone saying that some pro’s are riding 60-65% of the ftp for the bike and at 4w/kg that’s going to put you up there.
The general consensus is that if you want to run the Marathon you have to finish the bike like you could go out and do it again as you need those legs. The 70.3 Xiamen Qualifier is a good shout I have a friend who has qualified there.
What pros are doing that?
It all depends of how long it will take you to finish that specific course.
There’s a nice chart about this.
That’s why I’m questioning a 60-65% IF. Pros are riding between 4-4:30 bike splits on most courses. This chart would have them at 78-80%.
He is wrong.
Watch the post kona video of Lionel. I think he said he averaged 280w and it was his lowest ever there. 65% would mean a 430w ftp. Not true.
edit: My Thoughts After the 2019 Ironman World Championship - YouTube
Lionel said 290w.
Any idea what Lionel’s FTP is?
Edit: according to the follow article it’s 395 and he rode kona at a .79 IF.
and we know what you have to do when that happens
I don’t know, but watch his last video. He talks about a threshold workout he was doing at various effort levels and intervals duration. You’ll figure it out.
Lionel would be the last pro I would emulate in training. Perhaps now that he’s re aligned with David Tilbury Davis he will train reasonably, but his “enthusiasm” has always been his achilles heel.
You missed the point. Forget Lionel.
The idea here is just to say that PROs are not riding 60-65% of their FTP. I would say it’s closer to 80%.
Your Interviewee Norman had a 4:33 Kona bike split at around 70% IF over on that thread when I did the math.
@Nate_Pearson sounds trivial but maybe if you’re not running right now, try to gradually add some jump/skip rope… helps prime the lower legs (especially the feet), so when you start running, there’s already some strengthening that has taken place. One doesn’t replace the other but they do complement each other… annnnd you don’t need as much equipment or prep. Small sessions of 5 minutes at first and then add more time… add more moves, get double unders in, etc. It won’t affect your bike as much but it’ll help (re)awaken the muscles for running.
And who knows, maybe it’ll help you avoid some knee pain down the line. Grease that groove until you’re ready to start that training!
@craigmanning – thank you for the kind words!
@Nate_Pearson – just let me know when you are getting back into the pool. I would be happy to help!
Most of the data that I’ve seen for Pro IF is in the .78-.82 for full distance and .85-.9 for half distance
This seems to corroborate the .8 target pretty nicely: Power Analysis: The Best of Kona | TrainingPeaks
Mr Evans! You made Greta very happy with your coaching. Thank you!! 