GREG LYONS - Bike

The bike leg is usually raced as a time trial. No drafting (using the slip-stream of other riders to save energy). A long steady effort from 40k in the short distance races up to 180k in the full Ironman distance. It's a time to take on fuel and liquid, and the main problems encountered are from going out too hard and not being able to stay focused in the longer races.
The largest volume of one's training is done on the bike and at a comfortable aerobic pace to build endurance. I would recommend doing long rides alone as this enforces the abilities of staying focused and pacing oneself according to your perceived intensity.
Good books on training include Ed Burke's "Serious Cycling" and Joe Friel's "The Cyclist's Training Bible"

Bike

Training

Triathlon main

The bike is where most of your training time is spent. This is especially true when training for the longer distances. The main reason being that it is where a greater difference can be made to your overall time. If you doubled your training volume in all 3 disciplines you would probably achieve not much more than a few minutes of improvement on your swim or run times (not to mention the running injuries!), but you'd be likely to shave as much as half an hour of your Iroman bike split.

The process of riding a bike is relatively low-impact which means it is a good place to build fitness. If you start the season a few kilos heavier it's often a good idea to keep the running to a minimum and work on the bike until your fitness improves and your weight comes down.

RACING