Originally Posted by
Clownbike
Did you swap out the chain as well? The new system may need a different length and or width chain. Could also be a chain line situation. Have no experience with Bromptons, but changing chainrings and sprockets/ cassettes can effect chain requirements.
I haven't tried swapping out the chain yet. It's the same chain that is on the 2-speed system before I upgraded, so the width shouldn't be an issue. May try using a different length to see what happens.