>>1770904what actually is the use case though? explain it
that's merckx and hinault on a tandem btw. A normal tandem. The cheapest thing for you to do is to find a quality classic tandem. Good ones are often sold for absolute peanuts. A touring tandem will have tyre clearance for 'cruisey', the bars can be modified to that, a basket is easy as fuck to sus, and you could delete the rear crank or just have that person not pedal
I think what you really want though if you're prepared to spend on it, is a longtail cargo bike, like the surly big dummy, right?
any normal bike with a strong rear wheel and a rack can probably work, people double other people on racks all the time, but it's pretty sketchy, you're putting a much larger shear load on a tiny m5 bolt than it's designed for.
