Just wanted to share some info. about one of my recent rides, and toss out some advice.
I live in Texas and yes it's warming up here, so hydration is important--duh!
Anyway, I'm training my big butt for the Hotter Than Hell 100 in August and thus sometimes I aim to ride in the heat of the day.
on 6/9 I decide I need some heat, so I planned to leave at 12 noon and spend some time in the sun. And by the way, hardly any shade on my training course. So I fuel up well and hydrate beforehand--about an hour before departure to make sure all is well and digested.
With me I took some snax and the equivalent of five(5) 17 oz. water bottles of ice, water and Powerade. So I am weighted down pretty good. I have a hardtail mountain bike with 1.5" kenda slicks on which I train--not fast going.
Sorry, so I ride and stop a couple of times and eat my snax and drink. I warm up slow for a long time b/c of the temp. so this ride is time consuming. I went almost 40 miles in about 3 hours(bike) time and it was 95 degrees--98 heat index temp. with 37% humidity. I'm fine the entire way and I took in about all of the fluids I took with me. My point to this ramble, I took all this liquid with me and was fed and watered before I left--I still lost 4 1/2 pounds of body weight! Probably all water. You may FEEL perfect, but you are still losing fluid.
So watch yourself and others out there.