Aero Helmet, aero wheels. skin suit, or power meter? Which of these is most beneficial for Ironman racing? Before we look at which upgrade will shave seconds and minutes off of your time, let’s take a look at the goal of your Ironman bike ride. Your goal is not to simply ride as hard as you can. Your goal is to ride as fast as you can without ruining your run which means you’ll have to ride below what you’re capable of doing on the bike. If you start the run with overcooked legs, then all the time you gained on the bike will quickly disappear.
So, which upgrade is best for you? Aero helmets, aero wheels and a aero skin suit will allow you to be more aerodynamic, resulting in a faster bike split. A power meter has no aero advantage and will not make you faster from an aero advantage. However, there are plenty of good reasons to make this purchase as your first upgrade (I am assuming you already have TT bike). Here are the reasons why:
1) A power meter will allow you to evenly pace your efforts. An even paced effort is definitely worth time savings for the last 30 miles of the bike. Look at the bike splits of most Ironman athletes. Notice how much some people slow down half way through the bike.
2) Immediate feedback on the hills. A power meter will let you know exactly how hard you are pushing up the hills. Minimizing the surges on the bike is a huge part of your run success. Too many surges = a slow run or even a walk.
3) Target wattage. Assuming you have trained with your power meter, you (or your coach) should know exactly what wattage to ride at during the race. Using wattage and estimated time out on the course, you can predict the impact the ride will have on your run.
A power meter will not give you any aero advantages and make you faster on the bike on race day. However, I can assure you that the benefit of having a power meter to monitor your efforts on race day will result in an overall faster time for your Ironman. After a power meter, here are the upgrades I would make: Aero helmet, aero wheels, and finally a skin suit (the triathlon specific type).