The Swifts were designed for 33.9mm posts, but the build-up of
tolerance requires reaming of the seat tubes to make the post go
in both. The unfortunate result is loose fitting posts. Tightening the
clamps till they clamp securely can result in failure. My new black
frame is like that, I have to tighten the heck out of the QRs. A shim
is probably a good idea.
I wonder if a blind section of seat post, dropped into the seat tube,
wouldn't hold up the main seat post, with very low QR torque.
. . .
The idea is that the Swift has an adjustable height seat post.
This means that some (arbitrary) length of seat post may
safely be withdrawn from the seat tube.
I'm proposing to make up that length with a second piece
(of 33.9mm seat post) that resides somewhat permanently,
in the bottom of the seat tube.
The (mobile) seat post would then rest atop the semi-
permanent section.
If the semi-permanent section may fall out the bottom, a
small fixing bolt would prevent it from doing so. Looks like
the bottom bracket tube (so to speak) would foul it from
descending too far (into the bottom bracket shell region).
Provision would have to be made, if there were any expectation
of multiple riders requiring different-height seat posts.
If the semi-permanent s.p. section tended to fall out
(upwards, towards the seat tube opening) during folding
or storage, provision would need to be made for that
event (I'm thinking: just pay attention, in those circumstances,
and avoid being surprised by the loose section).
Seems to me this
Papillon approach has merit.
Ya gotta have a plan.