Assuming you have some experience racing, the biggest obstacle to a faster bike split is your ability to ride at a higher intensity and NOT your ability to ride for a longer distance. It’s a mistake to assume that if you want to ride fast for your next Ironman, then you should practice riding the distance. As you increase your distance it’s necessary to also dial down your intensity and this backing off of intensity compromises your speed. The more volume you log, the more your body needs to back off to make this happen and the end result is that your body becomes accustomed to riding at a lower intensity. Sure this will allow you to complete the race, but you are robbing yourself of speed.
You also have the problem of recovery and adaptation. Logging mega rides every weekend places a big load on your body and the time it takes to recover and adapt can often take more than a few days. If this time is spent trying to get in other training such as swimming and running, then your body heads into a survival mode and the subsequent training is often low quality. If you notice your power is dropping week after week, then it’s time to ditch the long rides.
How short? There are two things you need to consider when creating a workout – volume and intensity. Together, these determine the training stress of a ride. If you are using a power meter (you should have one if you are beyond your second year of racing), then Garmin or Training Peaks will have a Training Stress Score (TSS) for each ride. On your long rides, make it your goal to ride close to the TSS you plan to race at. For example, my Ironman bike TSS is usually in the 215 -240 range. I can create this score by riding hard intervals for about 3 hours and 30 minutes. If I were to ride at my ironman pace for 3:30, then my score would be much lower. By adjusting my intensity, I can achieve the same TSS as a 5:30 ride would give me. My wife and kids love these shorter rides!!
How often should you ride long? Long rides do have their place. While most of my rides are under 3:30, I will extend my distance close to 100 miles every so often just to test out my race day wattage. The purpose of these long rides is much different than my shorter, higher intensity rides. My goal is to rehearse my nutrition, hydration and pacing. I often finish these long rides with a short run to see how my legs hold up. Each athlete is different. Some of my athletes need to go through this more often because they need the psychological affirmation that they can ride the distance. Others can get by with 2 of these rides in their build up to Ironman.
Before you start logging mega miles to get you ready for your next Ironman, consider the purpose of each ride. What is your goal? Each athlete brings a different background to the sport so there is not a one size fits all approach. How much intensity, how often, and how much long distance will vary significantly from athlete to athlete. When you get the balance right between volume and intensity, expect to be blown away at your next race.