Originally Posted by
Leisesturm
Exactamente. When I bought a C&V road racer (pristine Raleigh Team USA) from 1984 it was your typical 27" x 1-1/4" clincher deal. When I was looking for something sportier (27 x 1-1/8) about all there was was Continental and Kenda. The Kenda's were something like 22TPI and so I went for the Continentals. I had to boot the front tire on the first ride I took on them. I had never booted a tire in 45 years of riding bikes. I had to boot the rear tire a couple of rides later. I GAVE the bike away this year because it was a Garage Queen that I never got around to converting to 700C. Rather than worry about what 27" tire has the lowest rolling resistance (they are all awful) I'd be thinking hard about a 700C conversion. In 27" there are only three sizes that survive into the 21st Century and none of them are made with the kind of quality or technologies that lead to a low rolling resistance.
Although there are few 27" tire options, the tried and true Panaracer Pasela is available in 27 x 1/18 and 1 1/4 and is a pretty good tire with fairly low rolling resistance. Swift tire markets essentially the same tire made by Panaracer in 27 x 1/3/8. If the OP has an older tandem those are perfectly decent tires.