Coca Cola also contains phosphoric acid which may provide additional phosphate to assist energy production. Like most runners, I find that some cola late in an ultra provides an energy boost. As long as I don't take too much at one time, cola doesn't bother my stomach. Individuals vary in their ability to absorb these sugars well. Some could drink the stuff all day, while others would end up with a bad stomach.
Some people have a hard time absorbing fructose, resulting in diarrhea or stomach cramps.
The fact that bikers can drink only Coca Cola in a bike ride doesn't necessarily imply that runners should do the same. For one thing, biking events are usually much shorter in duration than ultras. Biking places less stress on the digestive system than does running, so bikers can digest a wider range of carbohydrate sources than runners without distress. For example, I cannot drink Gatorade in a marathon or ultra without serious problems from it, yet I've done 50 mile bike rides where it worked fine. One drawback of sodas is that they are generally acid.