Dear Doc

My best guess is a metaphor/literal switch as frequently happens - last=stretched=long=not side by side but one behind the other. Since the key feature of a tandem (a word much misused by journalists in particular) is that the two 'driving' components are one behind the other, though working together (even the horse carriage thingy works the same way), it means that two on a bicycle are accommodated, of course, one behind the other, both (at least the cyclist on the front fondly hopes) pedalling away with equal gusto.

cheer

the sunshine warrior