Consider the following example. At the 2008 Ironman Arizona, the fastest bike split was 4:26:12, and the 50th-fastest bike split was 4:55:24—29 minutes and 12 seconds, or 10.9 percent, slower. Compare this gap to the corresponding gap in the run. The fastest run split was 2:46:38, and the 50th-fastest run split was 3:20:22—33 minutes and 44 seconds, or a full 20 percent, slower.
As you can see, in the bike leg, the top 50 performers were bunched close together, whereas in the run they were spread out. This pattern is apparent in every Ironman, and it is most certainly not evidence that the depth of running talent is less than the depth of cycling talent in these events. Rather, the pattern is seen as a consequence of the fact that athletes begin the bike leg with fresh legs, and thus most of the strong riders are able to perform at a level that matches their ability. But in the run, which begins with fatigued legs, most athletes fail to perform at a level that matches their ability. They bonk and lose huge chunks of time compared to the few competitors who manage to hold it together through the marathon.
Following are some tips that will help you avoid the all-too-common scenario of running poorly in the Ironman marathon