I had a similar experiance, I also chalked it up to not fueling myself well enough the night before or even just before the ride. my legs cramped up after 30 miles (with 40 to go) and I was dehydrated. Since then I read an article in a magazine,Ravensdale I think it was called a double century rider wrote on what to do when you dehydrate. Apperently your bodypanics that it doesn't have enough water so it traps any water that you drink in your stomach, which explains that bloated feeling you get. He said to eat salty things and that helps your body absorb water and stops it from trapping it in your stomach. I haven't had the problem since I read it (and hope never to again) had anyone ese ever heard of this before?