Tell us about your weekend ride

I don't even understand how anyone can spend more than maybe 8hrs on a bike. c.16 is madness.
Also how on earth do you eat so little during a ride?

All generalisations of physiology but (currently reading Faster by Dr Hutch)...

Slow enough, and with a well trained fat metabolism, and your body is powering you with mostly fat. The rate at which you're using carbs (fat burns in a carbohydrate flame) is low enough that the carbs can be replaced by eating (you can only take on a certain amount of carbs per hour). You can go pretty much forever at this pace.

Push a bit harder and your body needs more energy and this has to come from carbs (you're already at the limit of how fast you can process fat into energy). The carbs are being used faster than the body can take in new carbs so this can't go on forever, you'll eventually bonk but how long you can go for at this rate depends on the depletion rate. The average person has 1600-2000kcal of glycogen in the blood and liver - this is what you're depleting. A 200kcal an hour deficit will give you 8-10 hours before you go bang.

Push harder (up to and including race type pace) and you're way beyond what your body can take in and so the glycogen stores are depleted much more quickly, even if you ate like a horse. A 400-500kcal deficit will see you bonking in 4-5 hours; and sooner if you don't eat properly.

25kph average is the upper limit of my "all day" pace, it's closer to 20kph if it's hilly and I'm on fixed.

I can do 30kph average for a few hours, but I have to be careful what I eat. I've simply never averaged over 30kph for anything over that; mind you, I'm just an average fat bloke on a bike (with reasonable stamina and will/staying power).

I don't even understand how anyone can spend more than maybe 8hrs on a bike. c.16 is madness.

I like riding my bike. I'm not pushing myself on to put in a fast time or holding myself back for perfect pacing, just rolling along at the speed at which my legs want to go. I don't get depressed if my pace is a bit slower than I expect. It's a quiet mellow activity that (I've found so far) I can happily do all day.

Also how on earth do you eat so little during a ride?

I estimate I took in about 5000 cals, but there's some guesswork there. It soon adds up when you're porking entire 250g blocks of sainsburys basics red leicester cheese. How much of that I actually digested and was able to use as fuel is another question. 90g/hour of sugar would have been 6000 cals. Strava thinks I burned 9000, but 50mg/hour of caffeine and a suspect hrm means I don't really believe it.

My much shorter ride (see above) involved all the food, ever, and I was bonking fairly hard at the end.

You went faster.

I don't even understand how anyone can spend more than maybe 8hrs on a bike.

That surprised me, I'd thought you can spend more than that on the road.