I've fitted the 3 titanium cogs to the freehub, and measured the maximum lateral travel for the jockey wheels on the rear mech. No shifter as yet, although I'm planning to use a 3 speed SA shifter.
Those shifters won’t work, the travel is far out, you need to use a stock old style trigger and add a middle gear!
It seems that Clever Cycles have made it work:
https://clevercycles.com/blog/2017/03/03/want-a-9-speed-brompton-the-ti-parts-workshop-triple-cog-kit/
@Rhobbs started
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I've fitted the 3 titanium cogs to the freehub, and measured the maximum lateral travel for the jockey wheels on the rear mech. No shifter as yet, although I'm planning to use a 3 speed SA shifter.