When we bought our used tandem, it came with 25mm Gatorskins. On our first ride, I couldn't figure out why we had trouble simply maintaining 16 mph on the flat. My stoker puts out about 1/2 my watts, probably less when we were just starting our tandem career, but anyway. I'd heard that Gatorskins were slow, so I changed them out for a set of known fast road tires - I don't remember what. We tried it again, and night and day. The bike accelerated better, was more comfortable, and easily 1 mph faster at the same effort.
Another time, I rode with a very experienced female rider on a Populaire, a metric century sort of mini-brevet for those interested in getting into randonneuring. She was trying out a new set of Gatorskins. Not having flats on long strenuous rides is a good thing. After the ride she took them off and tried to give them away. No takers, so she just put them in the garbage.
I'm riding Conti 4KIIs or 5000 on my single. I can't remember my last flat though I have had one or two in the past couple of years. I do check my tires regularly and inflate before every ride - latex tubes. We are running 28mm 4KIIs on our tandem. Tandems are flat magnets, but we get very few flats and are totally happy with them. I have a pair of 32mm 5000 for when we wear those out in a few months.
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