On our new tandem we use gran bois 650B rims laced to White Industry disc hubs. The tires are gran bois hetre. At 42 mm width they have lots of air, so the ride is great. 650B Tires are a little harder to find, but we carry a spare out on tour. The outside diameter is very close to that of a 700C wheel with 28 mm tires. so you could switch to a 700C wheel with disc brakes if you were riding smooth pavement. The fork is an enve cross fork. Here's the best part of the story though: on rough roads, the 650B bike is noticeably quicker than our carbon tandem with 700C wheels. Good luck with your wheelset choice.