I'm pretty new here, just bought my bike a month ago and have taken a few 15-20 mile rides.

I pushed myself the other day and rode over 30 miles, but the last 7 or so weren't so pleasant. I was feeling totally exhausted. I'd eaten a little while before heading out and taken water with me but no food. I was averaging 17-18 mph for the first 1 1/4 hours but dropped to about 10-12 for the last 45 minutes or so, including a brief time when I was walking the bike to try to stretch out my muscles. What surprised me the most is that my arms were so tired. I know I need to work on my core strength and I have too much weight on my arms, but it just surprised me how tired I felt all over. I was feeling great until it was like I hit a wall and lost all my energy.

I'm wondering if this is because I should be snacking on something while riding. Is there a general rule for eating while riding longer distances? (For me, 30 is a pretty long distance.)