Ironman Bike Pacing

I'm trying to get a bit more methodical about how I pace the bike at IMCH. My two previous experiences at long course racing were chalk and cheese. At the Forestman, I significantly over-biked and by the time I rolled into T2 I was completely cooked and it led to a nice five and a half hour run / walk (mainly walk) to cover the last 26.2 miles. At the Outlaw I probably under-biked. I say probably because I don't really know, but I got off the bike feeling relatively fresh and was able to run the first 16 odd miles before cramp and fatigue set in. I had done virtually no running in the run up to the race so I believe that the problems I had in the second half of the run were more to do with lack of run conditioning and run volume rather than going too hard on the bike, but really, I'll never actually know.

I've owned a power meter for the last year and other than my 12 hr TT last year, I have not used it in real time on the bike; it's mainly been used for looking at my power after a training ride, so I started hunting round for how best to use it on the day and in my long training rides over the next 10 weeks. I want to be able to bike as fast as possible and then run as fast as possible. Ideally, I'd like to run a 3:45 marathon off the bike which is a big ask but I know I can do it if I prepare properly and race with my head, so the first part is to get the bike pacing nailed. But how?

Well, the internet is a great thing. I remember reading a while ago a great blog post on the Training Peaks website here; it's a very good read if you're preparing for an Ironman.

The crux of it is this table;

Across the top is the rider's Intensity Factor (IF). Very simplisticly, it's a percentage of the rider's functional threshold power, so riding at 75% IF (or 0.75) is 75% of their ftp (average best power of an hour). The numbers in each box are the Training Stress Score (TSS). This is a number that gives a value to the training stress for each activity as a function of its intensity and duration. Using this table, the aim is to keep your ride in the grey zone as this should mean that when you get off the bike the rider should be able to run.  If you push too hard and go into the orange and red areas, basically, you're stuffed. The general consensus seems to be that one should aim to keep between 70-80% (70% if not so strong on the bike, moving towards 80%  with more experience / bigger ftp etc)

So today I had another long ride planned but this time I set up my Garmin to not only display my actual power but also the average IF over the course of the ride and it proved very enlightening. First of all, I was bloddy shattered. I had two big weeks of over 12 hours; not a lot for a lot of IM athletes, but for me, they are big weeks. As I get older I need more recovery and when I rolled out this morning I could tell I was pretty tired. I'd run 10 miles yesterday and while it had been a pretty easy and relaxed run, it was still in my legs. I had planned to meet with Simon and Dale and within 2 minutes I could tell that they were going to be way faster than me. They were waiting for me a few miles up the road and I told them to go on without me because I was only going to hold them up and I just wanted to go at my own pace and effort. The IF displayed on the Garmin was 0.81 when I stopped with them, so already well over the IF needed for a well pace IM bike. The boys blasted up the A24 and I got on with the task of seeing if I could get the IF down.

I did; but it took 70 miles. In particular, hills are a real issue. This is obvious but actually seeing the IF spike as the road went up each time forced me to keep backing off. On the flats the IF would creep down but very, very slowly. The average IF at the halfway point was 0.790 but by the end of the ride I'd got it back down to 0.776. Final stats here;

So, what does this tell me:
1. The IMCH bike course is 2 laps. The first half seems fast and flat around the lake followed by a  lumpy second half. My initial thoughts had been to time trial the first half fast and then ease off and recover on the hills. This is plainly not going to work. If I'm hitting the first half of each lap too hard I'm not going to recover enough on the hills to keep the overall IF down. If anything, I'm going to have to keep the intensity right down early on in order to keep the overall average to a level that will allow me to run off the bike. This is what I did at the Outlaw but now I have a metric to actually follow to ensure that I keep to a plan.
2. An IF of 0.77 is too high. While I backed right off on the way home, despite a stiff head wind at times, the initial higher intensity fast start, even though quite short, bit harder than I would have thought and my legs were pretty dead by the time I got home. I'm going to need to bike at below 0.75 to stand a chance of a good run off the bike and keep this as even as possible over the two laps.
3. I've got to get my ftp back up. While I was tired and had a run in my legs, the chance of a 5:30hr bike seems pretty remote and 5:45 seems more realistic. This is fine if I can run a good sub4 marathon off the bike.

I'm doing ok, but lots still to do.