FTP target for a 3 hour half-iron bike
I have a goal to do a 3 hour split for the bike on a half-iron. My current FTP is 227 and weight is in the low 170s. I'd ballpark my split right now around 3:15. I know there are a lot of factors affecting how Watts turn to mph and the actual time, but would it be reasonable to look at it in percent terms and say my speed need to increase by about 8% (15 minutes out of 195), therefore my FTP needs to increase about the same? This will give me a goal FTP of around 245W. I wonder how that correlates to people's experiences.
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David, this is a great question, gets to the heart of race execution and utilizes a lot of the teachings of EN. I'm assuming this is for the Pacific Crest? If so, that's still 4 months away, and leads to my first answer: DON'T WORRY ABOUT THIS NOW! Your focus should be to keep on with the season training plan, and trying your best to improve your FTP via the workouts. Then, in another month, you'll be adding some longer rides at closer to race pace. Finally, with about 5-6 weeks to go, and again with 2-3 weeks to go, you;ll be doing your race rehearsals. Among other things, those rehearsals will give you your best data at just how you should dial in your power for race day.
At this point, use your "3 hour split" as a lodestone to keep you on track with your training. But don't let yourself become locked into it. And don't focus on how high your watts or mph should be to get to that target. Just let the process of training take you to whatever level of fitness it provides. Then, with a month or so to go, you can begin to think about what that fitness will allow you to do on race day, remembering this little aphorism: "Pay attention to your nutrition and your pace; your time and place will take care of themselves."
Now, having said all that, yes, there are ways you can try and figure out just what your FTP might need to be in order to achieve that 3 hour split, given your weight and the character of the bike course. One thing people sometimes use is a web site called bestbikesplit.com. It may even have the Pacific Crest course in its data base. Go there and poke around, you'll eventually figure out how to use its "calculator" to get the info you're asking for.
Power and speed are not linear. You can't think of it in those terms. If I were to double my watts I would not go twice as fast. It's a logarithmic progression.
There are often % of FTP numbers thrown around for the various distances. 80-85% FTP for a HIM/70.3 bike is an oft quoted number. For a 3+ hour ride it should probably be closer to 80%. That doesn't amount to a hill of beans unless properly trained to ride the distance at that %... and be able to run effectively after the bike. That's done through training and race rehearsals.
By far the best prediction tool I've ever used ... less then 2 minutes off on my Ironman bike split!