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Ok I know this is a stupid idea, but beer-driven musings… Is it possible to fit a SRAM AXS rear derailleur to a Brompton?
I know very little about Bromptons, other than I think their rear hub spacing is unique, and most Bromptons with rear derailleurs only seem to have 4-6 gears.
Brompton use unique derailleurs so different fitting from normal, also with the smaller wheel you'd be in danger of constantly bashing it. Standard derailleur is 2 speed and the newer version is 4 speed but they're mounted on the rear axle and chainstay so don't see it working without a lot of time and energy.
i've seen a Brompton 2 speed with eTap 11. They used a blipbox. It seemed to work OK.
I've considered it - I'm sure the MTB shifter would work well. Not sure if they are compatible.
I even started collecting old broken road shifters to adapt the shift innards, but ended up selling instead.
Unless they’ve changed recently Brompton don’t have a normal rear mech, they have a chain tensioner and a strange rotating pushy thing on the chainstay that moves one jockey wheel laterally (on a loose bushing) but not the rest of the tensioner. And only two rear sprockets.
I can’t see any conventional gears working without having a whole new rear end fabricated and new wheel built - and then will it still fold?
If you get a respaced rear triangle from kinetics you could run an Alfine with DI2 but I'm not sure whether a derailleur setup is possible. Ask Kinetics is probably your best sort of answer.
https://www.kinetics-online.co.uk/folding-bikes/brompton/
Here you go.
Brompton etap CHPT3, lightweight Brompton (brompton-shop.com)
https://www.brompton-shop.com/brompton-etap-chpt3/