It makes a huge difference what I eat before our Wednesday night hill rides. Because it's an evening ride but also hilly, it's 32-37 miles and anywhere from 1500-2500' elevation gain, both depending on sunset time. If I don't have a nice big bowl of brown rice three hours before we ride, I just start HURTING halfway through. It doesn't feel like a bonk, hunger, lack of energy or anything like that, it feels like I'm not in shape to do the ride. But that's not what it is, because if I eat properly the next time, I'm fine.

I had to discover this accidentally because it never felt like it was nutrition-related.