Originally Posted by torger

Yep it's a 3x10 Shimano 105 5700. It's not a vintage Cannondale though, it's the latest model (2018, unchanged from 2017 afaik, no tandems were made for 2019), but they use "vintage" parts still, I guess they bought it bulk and have for years to come. It uses the FSA Gossamer tandem crankset, and it only exists in 3x10 configuration. I kind of like the 3x10 for tandem though, fits our pedaling style quite well, so I don't feel a need to upgrade to 2x11.