This is the text of an email I sent to a customer who asked some questions about what makes a good touring bike:
A touring bike should be about comfort. Typically the tourist is not going to be doing too many short, hard efforts or sustained efforts in a paceline. Rather the tourist is concerned about riding at a moderate pace for a long time….6 or 7 hours or more.
-An extreme drop in height from the saddle to the handlebars, while allowing the competitive rider to take advantage of aerodynamics, might not be as comfortable on an all day slog at a moderate, steady pace.
-Tires are a major factor in comfort…use tires with 28mm minimum nominal width and 32mm or 35mm would be better. Don’t fall into the intuitive trap that hard skinny tires are faster. They aren’t and they beat you up on a long ride.
-You already mentioned fenders and we think they are essential, plus a bike doesn’t look right without them.
-Balance your load front and rear with more weight on the front (if the bike’s trail is suitable) On a good touring bike this will help stabilize the ride and steering. Your own weight on the bike is distributed about 60% rear and 40% front and adding more weight to the rear only can affect handling. We like Ostrich or Berthoud front rack top “rando” bags because they sit right on top of the front wheel/fender for a low center of gravity, they are easily accessible, and they have map cases.
-Drop handlebars offer more hand positions for long days and if the bars are up higher the drops are actually usable!
Get a traditionally spoked, cross three wheelset with minimum 32 spokes and 36 if you are heavier than 160 or so. Mavic or Velocity rims… they are the best.
Arguably, a good dynamo hub with a permanent headlight is a necessity. I think so.
We are big fans of leather saddles, for too many reasons to explain here.
A compact double crank set could work if you have a wide rear cassette and/or if you will not be doing much loaded touring. A triple is nice on loaded tours. 25 gear inches or less would be the recommended low range for loaded touring.
OK, you asked a loaded, open question. Hope I got close to answering it.