After several years serving my time as pilot to McNasty and Dick McT (both under 5'6" and around 10 stones) I bought another tandem to use with my son Aleks who is 6'5," fit and weighs 15 stones. He is now the pilot. (I am around 11 stones and about 5'8"). We can both comfortably ride 200k routes solo in around 10 hrs. We have ridden three 200k rides on the tandem and are finding we are taking around 2hrs longer on the tandem although this has been on hilly routes but not as hilly as the solo rides. My 200k rides with old git McNasty this year have been quicker than with Aleks. Aleks cadence is around 80pm and mine is between 100 and 110 pm and I do find my legs are sore due to the slower pedalling rate after a fairly short time and I am much more tired at the end of our rides. I wonder if anyone has an idea why we are so much slower and what we can do to solve the problem.