Use data points from prior training, testing, and racing to formulate an estimate on how much power you think you can hold for the X hours you think you'll be on the IMLP course, taking into account you would have to swim for Y minutes prior, and still need to run for Z hours. Then take that estimate, and experiment with it during a long training ride, and a short run after (can be as short as 20 minutes...usually you'll know right after the cobwebs in your legs clear). See how that feels. Adjust if necessary...rinse...repeat until you get it dialed in. Sometimes you don't even need to do the run if you shoot for a higher wattage on the ride because your legs are trashed. No big deal...it's good bike training and you know on race day that's too high a power goal.

Always keep in mind that how hard you bike will be impacted by how long you are out there swimming and how long you need to finish the run. Elite athletes who are only swimming for 55 minutes and running for 3:30 can bike at a harder effort because their overall race is a lot shorter than someone who'e swimming for 1:30 and running for 4:50.

An FTP test is just one of the data points you can use to come up with your initial estimates to test, and by no means is it the best data point. In my triathlete days, I knew I had to bike at a much lower percentage of my FTP than most typical athletes because I of the methods I described above...and I also validated my hypothesis with race experiences. To me...FTP is pretty low on the list for actual race day pacing for long course.

Thanks Jason, all good feedback, much of which I have already taken into consideration. I looked at my data from IMMT last year, but even though the bike courses are somewhat similar in total climbing, they are very different in terms of difficulty (I have ridden both). I can definitely use IMMT as a baseline, I was just hoping there might be a more scientific approach these days than just trial and error based on feel.

You looked into BestBikeSplit?

I long time ago, but thanks for the suggestion, I'll take another look!

Yes and no. My belief is you will want to find your target wattage on your race simulation days and long rides. By the time you toe the line, you should have a good idea of what sort of power you can sustain for 112 miles and still run well afterwords.

As for a calculation, you will find sources that say somewhere between .7 IF* and .75 IF. In reality it is probably closer to .65 IF to .8 IF. If you are really fast and competing for the overall, you will be closer to .8. If the bike is gonna take you 8 hours, you will be closer to .65. That said I just read an article about an overall AG winner of an IM (forgot the race, but I think it was a competitor.com article) that targeted .85. The point is any calculation is gonna be a huge range.

*Note IF is based of normalized power and NOT average power, but for an IM they should be close anyway. A ride with a .7 IF means your normalized power for the ride was 70% of your FTP.

what is everyone doing as IM bike simulation ride? just ride @IM goal power for the whole duration you are planning to complete the bike leg?
or more specific interval workouts?

Thanks

For a true race simulation, 112 miles at the hardest pace that you can ride that will allow a 45 minute to one hour run and 2.5 hour walk afterwards. That's what the majority of people seem to do in IM distance races, anyway.

---

***

No one running a 3:15 is walking more than the aid stations but I get your point :) I am not sure however if you can chalk all the walking you see during an ironman to overbiking. I think a lot of the people walking are also coasting a huge portion of the bike. They are just working with the fitness they have and are perhaps overreaching the task at hand in general. I tend to do decently well on the bike and I have found the effort level required to properly pace my 70.3 or 140.6 bike is quite high. I am on the gas working hard for the entire bike. When I got a power meter, I learned I was underbiking and not overbiking.

WRT race simulations, I will do the full bike distance a few times and then run 30 to 60 minutes afterwords with time at race pace. My belief is that if you are really prepared to do well in an ironman, riding 112 miles is not going to cost you a ton of recovery. I take detailed notes after these workouts gauging how I am feeling on the run and the bike and adjusting from there. These workouts should give you a good idea of what you are capable of. You don't need to do this every weekend because you can do better training than riding 112 miles at race pace, but you will want to do it a few times to dial in your race paces. There are a lot of different philosophies on this. Lionel Sanders wrote in his blog he did very little training at what was eventually his kona power. I am not Lionel Sanders though and I am not pacing the bike the same at all... At Kona he is busting ass to get to the front of the race and dealing with the pro race dynamics. I am racing my own race, which is a different strategy. I also do not have the same experience he has, so those race sim days are important for me.

About 10 or so years back there used to be a guideline (courtesy of Rick Ashburn IIRC) for pacing an IM bike leg that suggested a ride resulting in Training Stress Score of ~280-300 was about right for a reasonably wide range of abilities and which still meant the run wasn't compromised.

I've no idea if that guideline still holds today given the years of performances data available to assess since then but I thought it might be interesting to provide a chart showing the relationship between average speed / duration and the Intensity Factor required for an IM bike leg to result in a TSS of between 270 and 300.

Even if it still holds today, the guideline possibly begins to fall down a bit at the faster and slower ends of the spectrum.



Keep in mind TSS (and IF) is a function of Normalized Power and not Average Power, so the nature of a course and the manner it is paced, particularly ones with variable gradient terrain, will see the ratio of NP to AP vary a bit compared with flat courses.

---

http://www.cyclecoach.com
http://www.aerocoach.com.au

Same thing in an easy to use table. As no one else has posted it yet.

https://wpassets.trainingpeaks.com/wp-content/uploads/2017/01/howtocheatusingpowermeterinironman-2.png

Nice, hadn't seen that one before.

---

http://www.cyclecoach.com
http://www.aerocoach.com.au

When I temporarily had a premium best bike split membership I exported power based race sims of the actual course and rode on zwift a few times (not every weekend). You just place the file in the zwift workout folder. I would run off the bike (45-90min) and usually insert 10-20 minutes faster than race pace (somewhere between 70.3 and threshold), this gives a pretty good idea of where you are at but there are still many things to considert.

With my upcoming race I have had a lot of mixed signals, the simulated race has harder efforts up hills which I think feel harder on a trainer than outside. I couldn't get through all the sessions. It's been hotter in my earlier simulation sessions. In my final outdoor session the weather was cooler, I easily held 3.5h at race power plus 15mins 40w over. FTP tested 15w higher but I will not be increasing race power by IFx15, not enough time to test (1 week to IMNZ!), I will allow myself to go 5-10w higher on the 2nd half the bike, particularly the last qtr which is uphill ish and often into the wind.