All of this talk about "average speed" makes me anxious. We are new to tandem'ing, only able to get 100 miles in total before the Minnesota winter hit. Now have another 100 miles on with great anticipation for many more. Going out today and tomorrow weather permitting. I'm hugely competitive, former runner I'm all about times, speed and improvement. My stoker "wife" is new to the bike thing and not at all competitive so I have to really temper my energy to push the average MPH.... All that to say, at this point I am learning to enjoy the ride and time on the road without focusing on improving "my" time. Tandem is a "we" thing. I've wanted to ask the average milage questions but held off....
One of the first rules I learned when we purchased the bike is "keep the stoker happy" -- it's paying off with more miles!