I moved about 12 months ago to Hawaii where it's pretty much >85 deg all the time with relentless sun in the summer. I've started getting more serious about my training for an century in Sept. and have been getting bad headaches just about every ride over 20-30 minutes. Tylenol before and during rides helps some, but drinking more earlier and switching to sports drinks (at least 2 bottles/hour) hasn't really helped. I'm getting a little depressed about being able to ride for 6-7 hours in the middle of the day.
The only "solutions" I've found are to keep my heart rate below 75% of max (which makes it somewhat hard to get in good training) and to keep my head as cool as possible. I've toyed with the idea of putting an ice pack in my helmet, does anyone have a more practical suggestion (wet headband or skullcap maybe)?. I'm also going to visit a sports doc and see if there's anything more seriously wrong with me, like high blood pressure or something.