I'm surprised you need to eat anything at all on a short ride like that, at such a low BPM, and certainly nothing like 2.5 bottles of glucose! Just water to avoid dehydration should be enough.

I doubt the diet has anything to do with it. (In this case anyhow... certainly nutrition is critical for harder efforts).

A short bike ride that burns about 1250 kcal, which is another 50% on top of my normal daily requirements. So not that surprising that I'd need to take in 450 kcal really.

Certainly burns calories which you'll need to make up at some point, but it's a fairly short ride and I doubt you'd hit the wall if you didn't eat anything. I'm not saying you shouldn't eat it, everyone's body is different, and if I were in a 2hr race I'd probably be eating gels etc to guarantee maximal energy availability at all times. I just don't think you need it to be able to get round without running into trouble.

Anecdotal reference point: I go out every weekend with 3 friends, we do minimum 3.5 hours riding time in the local mountains, and the most any of us eat is something like a cereal bar and a banana. I can count on the fingers of one hand the amount of times any of us have bonked in the past 5 years...

I cycled competitively in my teens, and got a few ok results in my speciality (hill climb) at a national level, but not good enough to want to take it any further. Some of the friends I trained with went pro.

I trained 400 - 500 miles per week, riding anywhere from 10 to 140 miles per session. I'm 40 now and still cycle but just for pleasure and getting around now, slower than I was before but riding centuries is still no problem.

In short, I know exactly what the knock feels like.

I expect you are carb loading either the day before or in the morning before your rides, and that could easily give you enough stored glycogen to see you through a 2 hour ride.

I however was cycling to burn off fat that I'd built up during a few months of strength training, so the last thing I'm going to do is gorge on pasta the night before.