I am using Schwalbe Marathon Plus in 700 x 38C size on my 385 pound gross weight tandem. I would like to point out that the
original poster left out a major criteria and that is Comfort. So. in choosing tires, it is between Fast, Durability, and Comfort (ignoring cost)
I have chosen the Marathon Plus. I would like to point out that no tire because of structural design or construction has ANY effect on ride smoothness. ONLY ONE THING
affects smoothness that is tire pressure. The larger volume the tire has, the lower the potential pressure to support the weight and with the lower pressure
a greater ability to soak up road vibration. The lower pressure tire will ALWAYS be smoother than the higher pressure tire.
There are some who referred to different tire sidewalls as being stiffer than others and affecting the
ride smoothness but that is a falsehood. If you want to know how stiff your sidewall is and how much weight it alone will support, then let all the air
out of the tire. The sidewalls support zero weight. Except for the guys who are riding competitively, and I dont know of any Tandem races, I believe the safety of
the stoker is far ,more important than being 100 yards further down the road after a 20 mile ride. For any given pothole or rock that you hit, the larger the tire and lower
the pressure, the greater the liklihood that your tire will survive the impact. I say always run the largest size reputable tires that will fit on your tandem bike.
I also have a tandem bike with 26 inch wheels and a straight handlebar. On that tandem I run 26 x 2.4 inch knobby tires at 35 psi and boy is it a super pleasure
to ride. Technically speaking it should have the greatest rolling resistance, but after a couple hours riding the pavement, maybe I would get to the finish line a minute later than
my drop bar "race" tandem. Never again in my life do I ever want to ride on any kind of bike with skinny tires. I have no quarrel with any young racer dude who wants to ride
balls out on a skinny tire half bike but you should never ride that way with a helpless stoker on the back.
i