Originally Posted by WhyFi

This is similar to what I would go through previously. I would get what I called "the shakes" (not that kind). It didn't take that long, maybe a couple months or less, but regular fasted rides at moderate effort levels allowed me to reach that 90min threshold without problem. After that, I've been able to stretch it out. ~3 hours @90% without food is the limit that I reached in 2020, but I tend to bring at least a banana or granola bar on rides of 50+ miles, just in case the tummy grumbles.

Again, N = 1 and not to be taken as advice or even a non-dumb idea.