The OP is the 18.3. However, speed isn't important. Riding and enjoying the time with your stoker is. I know my marriage is stronger due to the tandem.


ON topic:
CT-VT-Trekker I built up a set of wheels using DT Swiss Tandem hubs for our 1000, we saved over 3lbs in weight with the wheel/tire combo and picked up around 2mph. Wheels were 36 spoke 42mm profile aluminum rims. Nothing too expensive or crazy, however a huge return on the investment for speed. With a little saddle time, a proper century ride and some decent pace-line work you could easily accomplish your goal.