Fueling and Hydration for Endurance
Hammer Nutrition has a lot of good tips on its site regarding fueling and hydration for endurance sports. The link above is to their guidebook, but if you go to www.hammernutrition.com and click on "Knowledge", they have more info.
Even with the guides, it takes a lot of trial and error to get a combination that works for a person. Everybody is different and there can be hundreds of variables in a ride. Heat, Humidity, degree of acclimation to local weather conditions, clothing, effort level, food eaten in the days leading up to the event, wind, etc. can all make changes that can tip the balance. Doing these types of events on a "pre-owned" kidney with some heavy duty medications thrown into the mix makes it a bit more difficult.
Link