Alright, now I'm on a roll. Like I said before, I don't really blog/write too much about fitting. It's a service for which I am paid (through Inside Out Sports) and I don't really make it a habit of giving away advice for "free." Actually, I do. One of the greatest things about walking into IOS if you are a triathlete is that there is SO MUCH KNOWLEDGE housed within its walls. I'm not really even talking about me (which I usually AM doing, harr harr). So, take that for what it's worth (which is a lot, actually).
So yesterday I mentioned juggling three things when it comes to triathlon bike fitting:
1) Aerodynamics of the position (i.e. system efficiency)
2) Comfort of the position (i.e. sustainability of #1)
3) Power output
One of the more common questions I hear is "will this affect my power?"
The answer is, almost certainly, "yes."
Now, before you get all scared about it let me tell you WHY it's "yes."
First of all, your power output will most probably be lower in your aero position. How much lower is a function of a couple of things:
1) Time spent in that position doing intervals
2) How low you are in that position (and various other angle/limitations/etc, basically the fit itself)
Generally it seems like - with practice - you can get that discrepancy to at or under 5%. Using a purely personal example if I ride as hard as I can for an hour on my road bike I am likely to put out somewhere around 300 watts (give or take). If I ride my tri position/bike as hard as I can for an hour, I am likely to put out somewhere around 280-290 watts, give or take.
I am not a shining example of practicing my tri position. Practice what I preach, not do as I do. Or something like that. In the reference above, I am averaging about 27ish mph on the tri bike. On the road bike, I'd be lucky to be much above 23-24 (on the same course with the same wheels).
So, it simply takes practice. Should you be willing to sacrifice a bit of power for the sake of a more efficient tri position? I say "yes."
Very, very rarely are you having to put out FTP+ power on your tri bike in triathlon racing. In fact, the only time I ever do that is when I am doing a sub 40k TT which essentially simply means I am doing the CMS 10 mile TT up in Concord...
See if you can tell what the difference is between these two POSITIONS (not the apparel/equipment).
In picture number 1 that is maybe mile 10 or so of the Rev3 Florida half from 2013 I believe. The second picture is somewhere in the middle of a 10 mi TT. In the first picture I am probably outputting somewhere around 80% of my FTP. In the second picture I am probably outputting 110% of my FTP.
It is very apparent what that does to my position. For the most part, both of these pictures have the same contact points. Or at least, within a few millimeters of being the same (slightly different aerobar extensions).
When trying to ouput that much power my upper body is completely engaged in the generation of that power. My hips have rolled "flatter," my lower back is torqued, my arms are locked and tense, my hands are gripping the extensions like they are on a roller coaster ride. My ENTIRE body is trying to put out more power.
In the first picture my hips are rolled forward a bit better, my back profile is far more relaxed (not quite as curved), my hands are resting lightly atop the extensions, my neck is a bit more relaxed, etc.
Again, nothing (much) has changed on the bike itself between those two pictures, what's changed is what my body has to do to affect power output. Number 2 becomes unsustainable after about 20-30 minutes (I don't know exactly as I've never tried to put out 110% for more than 20 minutes...). Number 1 should - in theory - be sustainable for...ever. Now, obviously that's not completely true but it really just depends on you - the rider.
Is your longest race of the year a half distance? Then you need to spend at LEAST your projected time in your aero position. You need to practice at race intensity. You need uninterrupted stretches of aero bar time. It's very difficult to completely replicate a race context in the "real world" in terms of course, distractions, output, fuel, etc... but you are doing yourself a disservice if you don't give it a real whirl.
That is how you help optimize that triathlon position and the resultant bike split. It involves a lot of trial and error and it involves a lot of PRACTICE. There is no magic bullet.
Find the right saddle (EVERYthing starts there). LEARN how to ride the bike in that position.
(both of those two things should be accomplished with an effective and knowledgeable fitter and a little trial and error with the saddle choice).
Then...wait for it.
Practice the s*** out of that position.