My body works like clockwork so what works for me is to always eat about an hour before the ride... that, ahem, seems to "force" the issue, allowing me to take care of it before I ever depart for the ride. Not a guarantee but pretty darned close!
also if it's a supported ride, don't pass up a sag stop... I did this on ONE century... and ended up peeing behind a plant that wasn't big enough to be called a shrub... lots of knowing looks and snickers from the other passing riders, but by then, frankly, I just didn't care!!! LOL
Have a great ride!
snapdragen... how not to pee on your shoes is definitely an important technique for all cyclists...
There is a fine line between "hobby" and "mental illness".