I've recently taken up mountain bike riding, checking out the local singletracks and firetrails. I've got quite a weak stomach and 50% of the time i find myself vomiting at about the 10km mark. After that i'm fine. If i make it past 10km without feeling anything i'm fine for the rest of the ride. The first time it was due to dairy consumption (or so i thought), and since then i cut out dairy altogether on the day of the ride, but it hasnt had much of an effect. Are there any precautions, supplements, or dietary regimes i should take up? I'm not a big person, and i'm definately not in need of losing weight. Diet is probably a big thing for me as i dont eat at regular intervals, just "when i feel hungry".