Originally Posted by
fietsbob
Ok a different thought .. kind of like #29..
use a hollow tube seatpost, run a cable loop out of the top of the seat post around the seat rails and back into the seat post , then run the 2 lengths of cable down the seat post tube,
and perhaps fix them to a stopper in the end of the seat post..
Or,with the other end secured in a plug that with enough cable length, slides down past the water bottle braze ons,
inside the seat tube , then you can fit a longer bolt in the bottle cage, to keep it from pulling back out out. ..
There used to be an antitheft device just like that. It fit inside the bottom of the seatpost, had a cable to a plug that dropped down the seat tube, and even came with a longer-than-normal bolt to keep the plug in place. Not difficult to remove, but would certainly take a thief by surprise.