Generating sustainable power on the bike is a direct function of how much raw power you are capable of producing. The more raw power you have at your disposal, the more your body can put it to good use. Employing a combination of aerobic rides, interval training, and lactate workouts, will help a rider to elevate his/her ability to sustain a solid level of power.
Did you know that the amount of power you are capable of producing can be significantly improved in as little as 7 – 10 weeks. Hours of aerobic riding will not optimize your power. In fact, a few simple and focused training sessions per week can target your ability to produce more power. When you combine these power workouts with aerobic base rides you are setting up a lethal combination.
Cycling coach Bill Edwards calls this Progressive Power Training. I would strongly recommend his book. This will give you a great understanding of how to maximize your time on the bike.