No one here disputes the usefulness of eating on centuries and ultras. During the double century mentioned above, I ended up finishing nearly an hour longer than I should have, simply because I unintentionally averaged only 120 kcal/hour over the second half. (While we're on this subject, it's also important to drink even if you don't feel like drinking. The reason is that you need water for the carbs to be absorbed. If you go much lower than 24 oz/hour, it inhibits your ability to digest carbs and you may even get nauseous.)
The question is what to do when your legs give out 40 miles into a ride. Here I say that you need to do more riding without on-the-bike carbs because you have insufficient glycogen stores and you need to work on that. Machka mentioned 2000 kcal in glycogen stores. For a trained cyclist who's not doing a time trial, 2000 kcal would easily last 60+ miles. You can count on 200 kcal/hour (conservatively) coming from fat, which, at 15 mph average, provides 800 out of 2000 kcal needed to go 60 miles.
The downside is that you will be less capable of sprinting towards the end of a 40/60 mile ride if you don't eat during the ride.
For bonus points, do what one of my linked studies did, and try some high intensity intervals after 40 miles on water.
Did something like that once. 200km through the night at 25kmh average with 2000m of climbing. On the way back met some friends on roadbikes (I was on my tourer) who wanted to go and do the hill I just went over one more time. About a 70km round trip ride. Why not? So I headed on back and pace lined it over that hill with the roadies at a 28kmh average. Ye gods did it hurt when I got back after 300km and no sleep in 32 hours. You can do it though. Eat enough and even at 300km in you have reserves. Its just having the willpower to go past the pain first.For bonus points, do what one of my linked studies did, and try some high intensity intervals after 40 miles on water.
I'll toss the misleading advice right back at you. Looking back many years to when I started riding again after a long layoff, I had to eat every half hour to keep my energy up. Otherwise I wouldn't have been able to ride hard enough to generate a training effect or maybe ride at all. I remember on a 50 mile ride finding myself sitting in a ditch while the world strobed around me. That's serious low blood sugar and it's dangerous. You have to walk before you can run. Too many of us posters use our current experience as a guide, forgetting how it might be for a rider who may not be a kid anymore and is just getting into it or back into it. That said, I did my first century solo at 18 on one candy bar, one orange, and 34 oz. of water, on a warm summer day. 17 oz. bottles were standard back then.
Hamster's advice is good once you have a base and can ride on fat like that. It's a good idea for training rides. But first, build a base. Around 1000 miles before summer is a good base.