Brompton 3 cog, (sprocket) rear Dérailleur

[BillN]

does anyone have a link or ideas regarding the following image, which I found on the web - 3 rear sprockets, looks like they are on the normal single 1-2 rear Brompton wheel and using the Brompton "chain pusher" to change the speeds.
Not sure if it is 1-2 speed or the 3-6 chain pusher, (lets call it a Dérailleur) - but I did not think that the Brompton Dérailleur would work over three speeds

[Arellcat]

I think 9-speed or 10-speed sprockets with suitable spacers will fit onto the 'cassette' rotor body.  Sometimes the chain tensioner must also be spaced out slightly from the dropout.  The chain pusher is almost at its limit for normal twin sprocket use, but will work if the overall throw is similar across 3 sprockets.  You can modify the Brompton 2-speed shifter with an in-between notch for the middle sprocket.

Here is a set of instructions for the task.

You might try 12t, 15t and 17t sprockets, with a bit of filing of the 12t to allow the standard snap ring to be used.

Or you can buy a titanium kit with all the hardware; it's anywhere from $350 to $500.

[mrcharly-YHT]

Is a franken-cassette, using a skinny chain and sprockets from 11 speed cassette to squeeze an extra sprocket in?

[BillN]

Thanks guys

I'm in the UK, so Clevercycles is out

The link "set of instructions for the task" - does not work - can you check and repost
"Access denied.
You have accessed a location on this server that is not available.
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Is the biggest rear sprocket that can be used with any such set up and a Brompton Chain pusher 17t? .... I suppose the more you get away from standard the more likely there could also be problems with the "fold"

[grams]

There's a copy of the instructions here (NB slightly dodgy Chinese mirror site, the original has fallen off the internet).

The Brompton chain pusher is bolted to a boss welded to the chain stay, and the upper jockey wheel does not move relative to the axle at all, so the size of the maximum sprocket is fixed.

[Arellcat]

This is the site from whence the PDF came:

https://www.evernote.com/shard/s3/sh/4bae9f26-2252-4be9-8229-314d0a13c754/3118242aa4dcc174f4c493cf5828165e

A larger largest sprocket on a Brompton will require the cutting away of the ends of the tubes by the dropout.

[BillN]

Thanks again - looks straightforward, () ..... but maybe near the limits for it to work reliably ()

I have a front 56 tooth Chainring fitted

presumably I can pick up an appropriate 10 speed Shimano cassette off eBay

[BillN]

So would this summarise the position, from the guide that has kindly been pointed to,

1). 3 new sprockets, (and spacers) [maybe 12t, 15t and 17t - 17 is the biggest that the Brompton will take?] from a Shimano 10 speed cassette - obviously "thinner" than the normal sprockets used by Brompton
2). Modify the Brompton 3 or 6 speed "chain pusher" (dérailleur) slightly - fitting a small spacer to push it out a little further - as the 3 or 6 speed chain pusher is mean't to work with a SA hub and only two sprockets on the rear
3). A new "10 speed" chain, (1/2" X 11/128") - narrower than the normal to work with the thiner sprockets - hopefully the front Chainring will be OK??
4). cut another groove in the 2 speed handle bar changer - so that there are three "click" positions

experts - do you see any problems?

[Philip Benstead]

does anyone have a link or ideas regarding the following image, which I found on the web - 3 rear sprockets, looks like they are on the normal single 1-2 rear Brompton wheel and using the Brompton "chain pusher" to change the speeds.
Not sure if it is 1-2 speed or the 3-6 chain pusher, (lets call it a Dérailleur) - but I did not think that the Brompton Dérailleur would work over three speeds

I have 6 speed Brompton   the spockets are 13 and 18, I think you may be able squease a 19 on?

[LittleWheelsandBig]

I suspect that the OP has long ago solved the issues or given it up as too difficult.

[Notfromrugby]

I have 6 speed Brompton   the spockets are 13 and 18, I think you may be able squease a 19 on?

Should be 12-16 (or 13-16)... anything bigger than 17 jams in the rear stay... you then need to file off material from the stay, which is suboptimal