I will assume you are talking about Type 1, juvenile onset diabetes. Not the increasingly common in the western hemisphere Type II, adult onset diabetes. Both have the name diabetes, but are completely unrelated diseases.
Main points. 1. Be reasonably healthy, other than the diabetes, before starting a tour. Follow a diet plan, keep blood glucose measurements within a decent range. Etc. Adding the physical exertion of long bike rides to a body that is on the edge is not advisable. 2. Use a blood glucose monitor while riding. Stop every hour or two and test. There are many very compact ones available. 3. Carry emergency food/glucose with you for the times your blood glucose is too low. 4. Reduce your insulin levels. Most likely your basal insulin will need to be cut a fair amount if you are going on an extended bike tour of a week or more. Insulin taken with food will also likely need to be reduced due to the body's metabolism, etc. using glucose without as much insulin needed. 5. Monitor blood glucose after the ride is over. It is very, very common for glucose levels to drop considerably in the hours after exercise is over. Even after eating a large supper, glucose levels can drop considerably in the middle of the night. 6. Build up to a long tour by riding lots now. Discover how your body reacts and how much food, insulin, etc. are needed to keep glucose levels in a normal range. Its a learning experience. 7. At my public library they have a book titled something like diabetes and extreme sports. Extreme sports being ultra distance runners and cyclists mainly. Something you do for 12-24 or more hours continously. It talks about adjustments to insulin levels.
