I've ridden centuries with little training and I've ridden them having gone into it strong. While you don't have to train for months, it makes it FAR easier if you do While I could finish the ride either way, I'd rather feel happy as I'm riding and I want to still have energy at the end. Proper training makes for a good experience all the way around though I have known people who can take months off then ride 100 miles like it's nothing. I'm not one of those people.