Tri-training plan Run heavy for marathon training?

This will be my 2nd ever Full Marathon. My goal is a sub 4 hour marathon. e.g. 3:55 - 3:59:59. Just anything under 4 and I will be stoked. I have a ways to go to get there. Lots of running experience, but not necessarily fast. Ran 3 1/2s this year with 1:53, 1:54, 1:56 times. In that order. all within 1 month. Hard to recover and get back up for races so close together.

The HIM was my first and I had 4 flats and it was ungodly hot that day. I over did it on the bike trying to make up for lost time and lots of cramping / tight legs by the time I got to the run so the run sucked. But it was my first HIM.

I'm now trying to reset and train focused on the full marathon sprinkled in with 2 olympic Tris, and 2 sprint Tris. My initial thought is that I try to do 2x swim, 3 x bike, and 4-5x run per week. reality is that typically I swim 1x week, bike (2 x spin 1x bike) and run 3 times per week The latter not seeming like much but really just need to add 1 swim per week, 1 more 'real' bike and 1 less spin, and maybe 1 more run per week.

I don't think you are going to hit your sub 4 marathon goal unless you set that as your dominant goal and severely limit your tri training. Of the 3 triathlon disciplines I'd focus on keeping swim going up to 3x a week and cut the bike down to 1.

Going with an IM plan won't get you the running fitness you are needing to go sub 4.

Find a good marathon specific training plan that most likely will be a 5x a week and then use swim as your recovery workout. Run the 4 triathlons with a focus on fun but don't waste time tapering and doing a bunch of speed work that would not fit with your plan.

I had a marathon PR (3:59:05) coming off of training for an Olympic distance race with about 4 weeks lead out. My goal was a sub 4. Not saying it will work for you but worth considering . . .

Here's the long version:

http://trited.blogspot.com/2012/02/can-you-cross-train-your-way-to....

Very Soft PR although those sub-19 5k's came when I was 17 years old. The Marathon PR was 20+ years later. The OP is interested in going sub 4 hours for a marathon based on a recent HIM. FWIW, the Marathon was by no means easy and I suffered greatly in the last 8 miles. I wouldn't recommend this as the optimal training option, but wanted to point out that it can be done that way.