Are the flanges on the 2speed Brompton derailleur jockey wheels so the control can behave as if indexed, with pusher simplyresting against flange...?

[SA3BR]

Are the flanges on the 2speed Brompton derailleur jockey wheels just so the control can behave as if indexed, with chain pusher resting but pressibg against flange in use, whereas no flange would mean an old school friction style shifter where user changes gear and/then adjusts pusher a tad to not rub on chain?.....

In which case if you replaced brompton 2 speed shifter with an old school friction thumb (left)shifter, the crud trapping capabilities of the flanges could be avoided* ?

*presumably you would keep the inside flange on the lower jockey, as the non derailleur tensioner has one there?

 

[Fastpedaller]

The chain pusher touches the flange to move the chain out or in when the shifter is moved in the required direction. It works the same if a friction shifter is used. Without the flanges the chain pusher would be touching the chain and create a terrible din and probably jam with the chain.

 

[SA3BR]

The chain pusher touches the flange to move the chain out or in when the shifter is moved in the required direction. It works the same if a friction shifter is used. Without the flanges the chain pusher would be touching the chain and create a terrible din and probably jam with the chain.

Thanks, But normal non folder front derailleurs just directly touch the chain and the osgood super champion rear derailleur also:

View: https://www.flickr.com/photos/speedplaypedals/7373407640/


so I presumed Brompton had a unique reason for adding the flanges..

EDIT upon further though a front derailleur has a parallelogram mechanism so always moves parallel to the chain and the osgood mech has a much longer distance between pivot and 'cage', so is presumably 'near enough parallel' to work?

EDIT if you added 2 vertical rollers to the Brompton derailleur 'cage' sides, perhaps you could ditch the extra 3 flanges?