gregf83 

Which part is wrong? The calorie figures for the running are accurate and the numbers for the bike look reasonable as well. The bottom line is running at a 6 min pace is far more intense than riding a bike at 14mph and will use far more calories.

While running a marathon, most of the calories come from glycogen stores. On a bike riding for 4+ hrs close to 50% of the energy would come from fat rather than glycogen. If you're burning 500-600 Cals/hr on the bike and you eat 250-300 Cals/hr of carbs you won't be exhausting your body's glycogen stores, so you can ride forever. Perhaps not forever, as your ass and other bits might get sore, but bonking won't be the limiting factor.