derailleur must have a long cage, or the chain won't be gathered adequately when folding.
wonder if the sort of widget Bike friday makes , a finger like piece, which bends over the chainring
so the folded chain slack
gets taken up there, as well as at the RD,, it is clamped around the BB shell
adding :it'sa DIY fabrication project now, but, the 3 pulley shorter cage ... for ground clearance ,
but 3rd pulley for chain wrap ... is re making a Design the Sun Tour RD
Used to make ..