i agree with gpsblake that itīs more mental than physical. in a tour of, say, a week, you can only learn more about the bike, how to fix things, pitch a tent, cook, etc. you donīt really feel whatīs it like touring.

then when youīre on a trip that lasts for several months itīs the idea that keep you going. when you face mountain after mountain(or other difficulties) itīs the determination that is the driving force rather than the fitness.