Generaly you train for endurance by doing LSD (Long, Slow Distance) rides. Rule of thumb is that during these rides you keep your efforts and heart rate in the aerobic zone (usually between 60-80% of max heart rate). Endurance training conditions the lungs and heart, and very importantly increases the number of mitochondria, the small subcellular "powerhouses" of the muscles.<br />Ride distances about 20% further than the longest race you plan to do. If you haven't done long distances in a while, then don't just jump on your bike and ride as far as you can. Gradually increase the distance by about 10% over a number of rides.