@bagpuss covers it well
Some detail differences:
1) its for touring trips, better than solo bikes there for us
But we didn't use our tandem for 12 years as the kids were between 2 and 12y.o.
Been out since then, loved it again.
2)A tandem is only 2 feet longer than a solo.
We often put it...
@non-fixie ...
Your wife sighs when she sees a church...
Mine, when she sees a pillbox🤪
https://www.retrobike.co.uk/threads/bikes-and-bunkers.481210/
Married life eh?
Who'd have guessed.
Looks like the ibis welds have been smoothed off, which is rare with ti or steel, much more common on the large aluminium joins.
I imagine there's mechanical assistance on most of these - although some look a little more freehand?
But raises that of the rider.
Performance demands are very differrent to riding for pleasure.
From an individual perspective, you can value a bike in many different ways, and small details of geometry make little difference.
Any retrobiker is also likely to appreciate a bike for what it was...
What's retro changes with time for sure - so if the component itself is a couple of decades old, that's a start.
But it needs a design difference to current standards.
Next year I think you could have a 20 year old 1x10 27.5er with shimano hydros and fox forks.
But you're free to define it...