Originally Posted by koala logs

I usually drink one whole bottle shortly before the ride. Typically less than 15 minutes before the ride and then pee right before I left.

I also take a huge meal around 30 minutes before the ride. Mostly rice (high, slow-burn carb) and some meat and cold milk chocolate drink. Many cycling articles advice against eating a huge meal shortly before a ride but it doesn't seem to have any negative effect on me. And that's for a non-stop 60 mile ride in the mountains. I also bring at least three bottles of water, with ~85F riding temps and rice-based fuel food.

The point is if you're rationing food and drink, you probably didn't bring enough. Eat and drink liberally during the ride as long as you don't feel stuffed.

It's probably the fueling and try to avoid standing too often to pedal on climbs long, hard, no stopping rides. It can ruin your pacing. Perhaps, improve your seated climbing with training. Train for higher cadence spinning, and even install smaller gear ratios.