Riding a loaded bicycle is a demanding physical challenge. Here are a few training tips that will help to prepare you for that challenge.
Start training at least four months before the planned departure date. One month of riding four to six days a week, either inside on a trainer or outside on the bike, is sufficient. You want to spin the bike at a high rate of revolutions per minute (RPM) -- at least 90 RPM -- and use easy gears. A good goal is to have from 300 to 600 miles, roughly 20 to 30 hours on a trainer, under your belt. Also, take time to work into a stretching routine. This will get your muscles, tendons, and ligaments ready for the next stage of training.
The goal for the next month is to build up riding strength in your body, once you have a good base of training. This is the stage where you gradually start mixing in more difficult training. Riding hills and structuring training to include intervals and sprint training are key to this stage. You want to mix this type of training in gradually while maintaining your spin rides between workout rides. Don't overdo it. Mix in easy rides and rest days. The goal is preparation, not overworking your body. Days you work on sprints should be the shortest riding days, and easy riding days should be longer. Remember, strength does not mean crushing huge gears. Higher rates of spinning will get you up the hills faster with less energy used. Hill climbing and strength training should be continued once or twice a week into the next stage of training.
This stage is meant to build up endurance for longer rides. Start by taking longer rides once or twice a week. By the end of this third month, you should be riding 40 to 50 miles a day, two days a week. Start toning down the strength riding for the sake of spending time in the saddle. Start enjoying the rides. Ride to places locally where you have either never been or haven't seen in a long time. Ride many hills and enjoy the views. Take a meal with you and stop to enjoy it.
This is the most important stage of training. About six weeks before your departure date, begin to carry weight on the bike as you ride -- particularly on the long endurance days. Begin slowly, carrying about 20 pounds or so, and work your way up to carrying all of your gear a couple of times a week for two weeks before your trip starts. You need this time to build strength in your ligaments, muscles, and tendons. This will help to avoid injuries and prepare you for an enjoyable trip.