Originally Posted by DnvrFox
Well, it can be a big deal, especially if it involves several thousand feet of climbing.
And, not anybody can ride 100 miles. If your bottom is not in shape, you can have terrible debilitating sores during the century. You should be doing more than "just riding." There should be a planned training period, with increasingly long times in the saddle, etc. Several web sites have training schedules available.
+1
Here is a collection of tips that might help.
http://www.bicyclistsofiowacity.org/ahcast/training.htm
BTW, I read that endurance champion Lon Haldeman was so tired during his first century ride that he had to lie down by the side of the road and take a nap.