Hi -
You may be able to store 2000 kcal of glycogen WHEN you're well-trained. It doesn't just appear in the muscles. You have to "teach" them - through repetitive training rides - that glycogen stores are required. Glycogen storage in muscle is an expensive process, metabolically speaking, and our bodies are programmed to be efficient. If you don't appear to need something, it goes away. When you stop using your muscles, the enzymes that help store muscle glycogen aren't made in the same quantity any more. It takes time to build the system up again.

Early in the season - particularly in a second season, where your body doesn't have as much memory of years of riding - you're not going to have enough storage to put down a 2-hour hard ride without adding fuel - and possibly electrolytes.

When you're more into the swing of things with your riding season, you may be able to head out the door for a 2-hour ride with a bottle of water and one of carb/electrolyte beverage and be perfectly good to go. That's because your body has learned to store more glycogen, and use it more efficiently. It may take several seasons before that system goes into "autopilot" as other posters have alluded to.

Did a club ride with a guy who's riding into shape yesterday. Seventy miles. He did great for - you guessed it - two hours. Up at the front, riding like one of the big dogs. No one guessed he was struggling. Then he bombed. Cramping AND bonking. He NEEDED fuel and electrolytes to get through the ride - as well as a lot of encouragement. Training up/getting fitter is hard. Don't make it harder on yourself by not fueling up as much as you need.