Built a new rear wheel for the
Gazelle Tandem yesterday. It's a 650B wheel with a Sturmey Archer 5-speed drum brake.
It's definitely not a featherweight at 4560 gram (
10 lbs) but it should be able to comfortably carry two people and offer the gearing and brakes.
The only problem was that I had to build it twice because I swapped the long and the short spokes so it was impossible to center the first time around.
Still, even with just half the wheel built it was still a prettty stiff rim.
Parts: