IM run training

Normally, I would say to aim for a few 20 milers, but with IM training, you have to spread your energy over 3 disciplines.  For you, this would mean doing several 3+ hour runs, which I believe would hurt you more than help you.  You do have the benefit of the fitness gained from your other two disciplines.  So in your case, my opinion would be to stick to 2 1/2 hour runs and even then, only as you approach your race.

In the interests of full disclosure, I would point out that I've never done any triathlon, but I know from my own experience, that more isn't always better.  Good luck with your race Crux  

Crux I am slower than you and won't run more than 2.5 hours (in fact this time its been only just over 2).  The marathon after the rest of it is not like a standalone marathon and is a lot about mind over matter.

Better to get off the bike feeling strong enough to shuffle round the 4 laps (or whatever)

And I was reliably informed that it takes longer to recover from the run than the bike so you don't want to compromise other parts of your training by doing much longer runs

That is my view but there will be others

My long runs last year were in the range of 2 - 2.5 hours and I ended up running the first half of the marathon and then run walking until about 30K and then shuffling / running to the end. This year I have run up to 3 hours in training and found running the day after a long ride much easier, experience I guess. So much of  a IM marathon as Rio says is in the mind,  for me it definitely helps that I have run a lot of standalone marathons / ultras I recognise all the aches and pains which come along from 18 miles onwards as old friends.

In short Crux I would say a 17 mile run is going to be enough to get you around, it depends how long you have to until your race as to whether you want to try a longer run. If there is 3 weeks or less left your better off sticking with what you have done.

If you have 3 hours to spare, then running for an hour after cycling for 2 is probably going to be more beneficial than running for all 3.  Shorter recovery too.

Crux, I roughly followed the Fink book but listen more to my body telling me it was tired and done enough for that week rather than get on with what the book said. I did a longest run of 3hr 23 mins for 20 miles about 3 1/2 weeks out. My longest run after that was 12 miles just over 2 weeks prior. I don't know what time you are planning but in my book 9mm pace is good going. All my runs were virtually on the 10mm pace knowing I wouldn't do this on the day but gave me confidence.

I wanted to do about 6 hrs for the run section. At Enduroman the route is hard, 24 laps of steady downhill on one side of the course, flattish around the bottom and then 3 sections of hard climb back up and around the end of the lap. The climbs were always walking but the rest I ran, steady away. I finished the marathon in 6hr 8 mins which included transition time from finishing the bike.

I agree with others, if you are well trained, don't kill yourself on the bike then the run has a lot of mental battle to it but I was in the right frame of mind before the day that hell would have to freeze over for me not to finish. Fortunately I didn't cramp up but I had drank well and fed well all day. 6 hours ain't no record pace but unlike Dubai Dave I've never ran more than a half marathon other than 4 of my long training runs in the last 2 months. Experience will count if you have alrready done a marathon before I would guess.

I suppose it depends on if you are after a sub 13 or 14 hour time and what your own expectations are prior to the day. Mine had an order of 1. I must not die 2. I must finish 3. I don't care what time I finish in 4. If I finish sub 15 that would be great but the overiding factor for the day was, I must enjoy myself. I had a smile on my face most of the day and what a feeling to finish.

Whatever train well and make your own "luck" 

Thanks for the advice everyone. I still have till September so plenty of time yet. I may just try one 20 miler a month out

I have got a good few 2hr ride+1hr run bricks planned over the next few months, so hopefully that will help as suggested.

You do have the benefit of the fitness gained from your other two disciplines.  So in your case, my opinion would be to stick to 2 1/2 hour runs and even then, only as you approach your race.

if you can do regular 2.5 hr runs over the next 2 months then you will get fitter, stronger and will build your endurance.

If you are also riding long each week as well (ie 6 hr ride) then you will have a really solid day.

I normally have a 2.5 hr cap, and I run this on a Thursday into work. I might do a very easy spin home on the bike, but I have Friday off, swim long on saturday, and ride long on a Sunday.  That way I hit all the key long sessions each week.

I followed the Beginners Triathlete training last year and it did have a 3hr run, and I think a 2hr 40. As I was planning a run/walk strategy I used that on the long sessions.

Didn't have any major issues from the 3h run session and think I went 19 miles or so in that time. However I was lucky in that I was biking mid-week with a half day off work and running on a Sunday so had recovery time between the two. If you have to do the big ride and run close together this makes it harder and riskier.

This year my last long run was a marathon in April and haven't run over 2hrs since then - but then I am expecting to suffer this year!

IM is a long run after a long bike after a long swim. Keep it very simple. Build your training aroung two main things. Number one recovery and number two the long run 'after' the long bike. If you build up to bricks of 4-5 hour bike and 2-3 hour run you will do more to ensure your IM success than with any other sessions. If you are getting tired then you are doing too much other stuff.

Speed if quite secondary to the session itself, it is all about specific training using the energy pathways availiable to you in the actual race. And the added benefit of low glycogen training in the depleted state you will inevitably be in during the last hour or two of the brick.