That is indeed why you don´t see them collapsing and also why the finals are much longer nowadays. Riders train their guts to be able to eat up to 120g of carbs per hour, for the whole duration of the race.
I am far FAR from the tour de france but I do train for and run ultramarathons.
When I started the general guidance seemed to be about 200 calories (50g of carbs) per hour during training and races. I followed that or a little above for a long time, and constantly had problems both physically and cognitively near the end of races.
It took about a year to get used to fueling heavier (for me...about 400 calories per hour or 100g). Lots of figuring out digestion and timing and sources and other factors. But once I got there it was transformative...I could push much harder for much longer without a deep bonk and recovery was faster. More importantly, my ability to think/plan/make decisions at the end of races was orders of magnitude better.
I'd bet if you went to an aid station around 80 miles on a 100mile ultra marathon you could pretty reliably identify who had been on the 200cal end of the spectrum and who had been on the 400 + end.
At 250w average during a 5 hour ride I'm burning like 1000 calories per hour or something mething close. Glycogen reserves are 2000 calories from a quick Google search, so that's 3k calories I need to make up for or 600 per hour. I'm sure there's a bunch of stuff I'm missing but 400 definitely makes more sense than 200
What you're missing is fat metabolism. If you're metabolically healthy (which you must be if you can hold 250W for hours) then you can make up the difference by converting stored fat into glycogen.
Since my first ultra, Ive been fascinated by the idea of adapting to increased fueling and have tried to apply periodization principles to how I eat. 23 miles into a 33 race, I completely stopped being able to process food at around 150-250 cals/hr (mostly carbs and some fats)
speaking from experience - I puked during a fair number of runs in the process of getting there. I mix calories in my hydration with gels just to try and get the balance right. Its not stable but its better after about 4 years of work. I have ound that if I don't do a good job of eating, what you describe happens about 6-10 miles AFTER I stopped caloric intake.
Yeah, some of the modern nutrition stuff like gels work really well. I did a 115 mile road bike ride on Sunday and kept eating gels and... I'm not going to say I was super fresh or anything by the end of that, but I was still feeling pretty good.
Yeah, I bought a huge bulk pack online, and then it was okay. But when you need a couple a week it quickly adds up in cost. Same with bars, which I sometimes prefer over gels for longer rides to not just have gels in my stomach. I've tried to bake some bars myself, or make some rice cakes from Velochef ( https://www.rouleur.cc/blogs/desire-journal/velochef-henrik-... ) instead.
When I started the general guidance seemed to be about 200 calories (50g of carbs) per hour during training and races. I followed that or a little above for a long time, and constantly had problems both physically and cognitively near the end of races.
It took about a year to get used to fueling heavier (for me...about 400 calories per hour or 100g). Lots of figuring out digestion and timing and sources and other factors. But once I got there it was transformative...I could push much harder for much longer without a deep bonk and recovery was faster. More importantly, my ability to think/plan/make decisions at the end of races was orders of magnitude better.
I'd bet if you went to an aid station around 80 miles on a 100mile ultra marathon you could pretty reliably identify who had been on the 200cal end of the spectrum and who had been on the 400 + end.