Originally Posted by
ivan_yulaev
That aside, if you're doing a century, you will bonk at ~70 miles in without nutrition. Glycogen supply is about 3000 calories, this should give you 50-80 miles (or so), but I'd be surprised if anyone could do 100 without any sort of calorie intake, without bonking.
How quickly you run out of glycogen is a function of how hard your are riding. If you want to extend the distance you ride without food just ride easier. At lower exercise intensites your body will use a higher percentage of fat. As the intensity increases and you ride closer to threshold the % of glycogen usage will go up and you'll burn through your reserves faster.
So, if you don't want to bonk at 80 miles you have only 2 options: eat more during the ride (250-300 Cals/hr) or ride slower. Carbo loading can be effective for races (probably more useful for marathons) but isn't necessary for long endurance rides.
edit: I started typing, went for coffee and then repeated what others have said.