I really should have thought in terms of kj, not hours.
under 3000kj, I don’t bring food. Over 3000, yes. If it’s a 4hr 3000kj ride, then it’s easy endurance and I’m just burning fat (FTP is around 340). If it’s a 3 hr, 3000kj tempo ride, that last 30min is difficult but doable.
4hrs+ with sweet spot climbs, well, that’s going over that 3000kj budget, and if I don’t eat, I’m going to bonk.
Some no food rides:
https://www.strava.com/activities/2370763878
https://www.strava.com/activities/2441743106
https://www.strava.com/activities/2446852320
A food ride
https://www.strava.com/activities/2377798740
A race – 3 Clif gels (I’ll bring 3 gels to a 2hr race)