Always on the mind of the Ironman Triathlete: how hard should I ride if I want to save enough energy to run a good marathon? In the 2010 Ironman Florida, if you rode a 6:06 bike split and ran a 4:57 marathon, you struck the perfect balance. Also see our analysis of Average Finish Times and our complete Ironman Florida coverage.
Another way to look at the equation, at least on the Ironman Florida course: marathon time = 0.81 times your bike split. That's what the data for 2301 athletes suggests, though the degree of confidence is a bit mixed. Those in the upper left quadrant generally left it on the bike course, burned out on the run. Conversely, those in the lower right ran better than expected after a slow bike split. The others: smooth, steady, solid balance, and comfortable finishes.