Ironman Bike Set Up

Ironman Bike Set Up
Comfort is key for Ironman racing. Do not change anything relating to your bike position in the last 1,000 miles before your Ironman. The elite have been known to change from a road to triathlon bike 6 weeks before they race, however they will cover over 1,000 miles (1600 km).
Wheels
Make sure that your pair of wheels are relevant for the course you are doing. Wind conditions will affect your choice of aero or lightweight wheels. Choice of bars depends on the amount of climbing, descending or flat straight roads. Standard comfortable drop handlebars offer more choice of positions which is more important for Ironman racing. Have tyres that are appropriate for the road surface.
Gears
Bike gears No one ever asks what gears you use, they are more interested in times?
Use your fitness not your strength. Have easier gears than you think you need so you use your fitness; there is no shame in using a 25 size sprocket or bigger. Most courses are often lapped based and have some hills which deplete strength. This means having a cassette with the right gearing for the terrain is important. 
Power Meters
You will be amazed how little power you generate down a hill and how much you overuse your power up a hill. For a well paced ride, a power meter is a vital tool to measure your effort in watts. Your target average for the Ironman bike is between 78-85%. Heart rate is only part of the picture. Complete a 30 minute time trial effort. If your average power for the test is 220 watts then your target average for the Ironman bike is 78-85% (171-187 watts). You can still cross reference between keeping your heart rate below your anaerobic threshold and keeping your watts in the Ironman zone. 
Bike Position
Learn to ride aero for long periods of time. Many triathletes ride for hours but fail to ride in the aero position. This occurs from group riding where an aero position is unsafe, that is why a very large percentage of your riding must be solo. Being comfortable is vital so you can stay aero and not be distracted by moving about on the bike. Too low a position will badly affect power, breathing and your ability to digest your food.
Adopting a forward seat position will reduce stress on the hamstrings