YMMV.

I found that if I eat before riding, it seems to kick my body into a "Feed me, Seymour" mode. I have to keep eating. If I don't, I bonk. However, if I don't eat before riding, my system relies on its energy stores and lasts for up to 2+ hours before I need to start eating.

As I said, YMMV. So play around with it. Also, get warmed up before the ride as others have said.