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 I wonder if there is anything that would allow 3 flanges to be dropped .

 

[Kell]

I've seen some high-end modded Bromptons using derailleurs without the flanges.

Bane of my life. Cycling around Hyde Park (where there is a sand horse track) it used to get full of crud and I went through this every month.


View: https://www.youtube.com/watch?v=E4nh0aEiBeI

 

[wafter]

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 I wonder if there is anything that would allow 3 flanges to be dropped .

The differentiator is that on a traditional derailleur the force that moves the jockey wheels laterally is transferred from the cage through the jockey wheel bearings. Conversely the jockey wheels on the Brompton are free-floating laterally so the flanges are necessary for the pusher to act upon to move them.

I assume this is because there's insufficient space for a traditional derailleur on account of the small wheels and fold. Ultimately whichever way you go, if you wish to move the chain laterally it's going to involve some sliding friction between components and while a bit weird the Brompton system seems capable enough.

 

[rogerzilla]

Brompton derailleurs allow changing (at the lever) while not pedalling because of the springs in the cable run. They presumably wanted to make it idiot-proof. The chain won't actually move sprockets until you pedal, but the gear can be selected even if stationary.

 

[Kell]

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?

My chain pusher actually wore out as it was constantly touching the flanges. I did think it must be possible to set it up with the limit screws so it's not constantly rubbing, but when I tried, I then had difficulty switching gears.

 

[SA3BR]

The differentiator is that on a traditional [ rear] derailleur the force that moves the jockey wheels laterally is transferred from the cage through the jockey wheel bearings. Conversely the jockey wheels on the Brompton are free-floating laterally so the flanges are necessary for the pusher to act upon to move them.

..if you wish to move the chain laterally it's going to involve some sliding friction between components and while a bit weird the Brompton system seems capable enough.

If the chain pusher had a parallel action like a conventional front chainring changer (or a close enough to parallel action ), perhaps that would obviate the need for flanges?

The pusher end stop is meant to mean it isn t rubbing the flange constantly apart from due to bumps?

 

[SA3BR]

The differentiator is that on a traditional derailleur the force that moves the jockey wheels laterally is transferred from the cage through the jockey wheel bearings. Conversely the [flanged] jockey wheels on the Brompton are free-floating laterally....

Given that the new 4/12 speed derailleur loses the flanges from the upper pulley/idler but keeps them on the axially free idler on the separate tensioner/chain gatherer, why not avoid all flanges by making the derailleur a conventional (but still rearward*) short cage two pulley derailleur, with, again, a separate chain gatherer whose job is now only to gather the chain upon folding (perhaps using a wide roller/pin which does not contact the chain (much?) when bike is ridden).

Sounds a bit Birdy like I suppose however Brompton would require it to be able to be folded in any gear which I think the above could allow...?

*Dahon briefly fitted a reverse shortcage derailleur, but I think such things existed in the early days of derailleurs, so no patent problems?

EDIT found a link, its the neos and does indeed have vintage inspiration:

https://www.disraeligears.co.uk/site/dahon_neos_derailleur.html

Also used by Tern it seems.

 

[SA3BR]

Does silence mean dissent?

 

[Fastpedaller]

Given that the new 4/12 speed derailleur loses the flanges from the upper pulley/idler but keeps them on the axially free idler on the separate tensioner/chain gatherer, why not avoid all flanges by making the derailleur a conventional (but still rearward*) short cage two pulley derailleur, with, again, a separate chain gatherer whose job is now only to gather the chain upon folding (perhaps using a wide roller/pin which does not contact the chain (much?) when bike is ridden).

Sounds a bit Birdy like I suppose however Brompton would require it to be able to be folded in any gear which I think the above could allow...?

*Dahon briefly fitted a reverse shortcage derailleur, but I think such things existed in the early days of derailleurs, so no patent problems?

EDIT found a link, its the neos and does indeed have vintage inspiration:

https://www.disraeligears.co.uk/site/dahon_neos_derailleur.html

Also used by Tern it seems.

I've just bought a Shimano derailleur (shadow type) to experiment whether it will work on my Brompton - 2007 superlight 2 speed currently modified to 3 sprockets and 2 chainrings with a front derailleur. I add that the rear sprockets only range from 12 to 15T, so not much variation in chain length due to the rear sprockets. I anticipate gearchanges will work fine in use, and with such a close ratio on the rear the mech won't be close to the ground unless I venture into the small ring. Folding may not be an issue - If the long-cage mech is long enough to cope with the fold (albeit with the chain on the big ring). My aim is to move to standard parts - although I accept the chain pusher works well.

 

[wafter]

Given that the new 4/12 speed derailleur loses the flanges from the upper pulley/idler but keeps them on the axially free idler on the separate tensioner/chain gatherer, why not avoid all flanges by making the derailleur a conventional (but still rearward*) short cage two pulley derailleur, with, again, a separate chain gatherer whose job is now only to gather the chain upon folding (perhaps using a wide roller/pin which does not contact the chain (much?) when bike is ridden).

Sounds a bit Birdy like I suppose however Brompton would require it to be able to be folded in any gear which I think the above could allow...?

*Dahon briefly fitted a reverse shortcage derailleur, but I think such things existed in the early days of derailleurs, so no patent problems?

EDIT found a link, its the neos and does indeed have vintage inspiration:

https://www.disraeligears.co.uk/site/dahon_neos_derailleur.html

Also used by Tern it seems.

Yup - I see no obvious reason you couldn't do this (other perhaps than the massive range of motion the current setup has to accommodate the fold). However, I suspect it comes down to the usual cost v. performance situation; the current setup is probably dirt cheap and while not nec. the last word in engineering refinement IMO perfectly fit for purpose.

If Brompton suddently decided to chuck a lot of money into meaningful improvements on thier existing bikes, I can think of a lot of areas I'd prioritise over the gear selection setup.