Brompton owners

M cables just happen to be right size for m stem & JK mid riser.

Hi designed the bar to work as a reduction from M or to turn S into an M. No coincidence!

Send me a message I can piece together a kit from my spares box

Will do. Message coming.

Thanks for the info, didn't know that; everyday's a school day!

What do people think of the MiniMODs 2->3 sprocket kit?

The backstory:
I have a 6spd bromp which is generally great - the two middle gears 51"/63" are a nice combo for cruising around south London - but I want the 33" granny gear to be a bit lower to get up more hills further afield when carrying a little more weight.

The Brompton suggested 44t chainring would give me a granny gear of 29", but my middle gears would be 45"/56" (and then 71"/87"), which is going to suck.

However, a 47t chainring and the 12/15/17t MiniMODS triple would give me a better granny at 29", whilst keeping the middle gears of 51"/64" - and it's a ton cheaper than the amazing rohloff or whatever options.

What's the catch, then? Other than - how do I figure out what chain length I need...?

MiniMODs 2->3 sprocket kit?

I'm looking to get this to put onto a single speed for my GF. Really interested to know anybody's experience with how well it works?

What shifter were you thinking of using for the 3 speed sprocket?

haven't really thought about shifter yet - maybe https://www.sjscycles.co.uk/gear-shifters/sunrace-m90-friction-thumbshifter-left-hand/ - thumbies are good, I like thumbies

I was looking at the DT Swiss lever, which its seems is quite popular. But pricey. It's quite pricey.

This blog lists a few options;
http://www.loro.co.jp/blog/east/2021/07/brompton-100.html

If you only want very low gears occasionally, a double chainset is the way to go. No front mech needed.

fitted a few, friction shifter is best sunrace m90 for sure

the system requires a bit more fine tuning, either fit an alfine or just hold out for brompton to progress; there was a prototype sold on ebay last summer with a different style DR system and a press release recently had the same style system on the photo (press release not about the DR)

got quite a hoard of parts on the bay atm; superlight front wheel currently at 99p!

https://www.ebay.co.uk/usr/thebromptonman

that's actually a good shout.... hmmmm

that looks cool, but I was thinking more friction shift than be continually grumbling with indexing - this person has made it work with XTR rapidfire, but it doesn't seem that well indexed (sounds like it would skip under load tbh...) https://www.youtube.com/watch?v=cipjOJzAXTM

Using an indexed shifter is a no go from my testing, if you have any care for it indexing correctly that is...

I have a 2 speed gearing query.

From the ratio charts my ideal set up would be 50t chainring with 14 and 16
sprockets.

Is this a feasible set up or am l missing something?

The 14t sprocket does not appear to be readily available?

doesn't the minimods kit come with a sturmey archer 3sp indexed thumb shifter?

How do you only get the XTR to click 3 times? Does anyone know the S2L pull ratio?

Is this a feasible set up or am l missing something?

The 14t sprocket does not appear to be readily available?

My understanding is that the Brompton 2-speed sprockets were matched sets of specific ratios to yield half-step gearing in combination with a 3-speed hub gear. Originally it was 13t + 15t to work with the standard spacing of the SACHS/SRAM 3-speed hub, then 12t + 16t for the Brompton Wide Range Sturmey Archer hub that changed to a 9-spline fitting. The lower sprocket of each has a standard tooth pattern, while the upper one has alternating low teeth to help with gear changing.

The Brompton specification document is available to download here:
https://www.vlerickfietsen.be/download-asset/bd785b7e-0766-11ea-8b7e-005056985c04

Which confirms that it is the inner sprocket which is 1.8mm thick and the smaller outer sprocket which is 3.1mm, so the one in stock at SJS Cycles looks like it should work.

SJS Cycles have a 3 / 32" 14t 9-spline sprocket. Maybe @sbbohr and SJS can confirm compatibility:
https://www.sjscycles.co.uk/sprockets/sturmey-archer-14t-sprocket-332-flat-9-spline-hsl912/

It is also available at:
https://hollandbikeshop.com/en-gb/bicycle-parts-city-bike/bicycle-sprockets/rear-sprocket-sturmey-archer/sprocket-14t-flat-3-32-9-spline-hsl-912/

Thanks for your response.

I should have made it clearer l am looking at the two speed derailleur only option here so no hub gear attached.

Looking at the spec document for 2 spd derailleur the outer cog should be at 3.1mm and inner cog at 1.8mm.

Does this mean 1/8” outer and 3/32” inner as the listings are in mm not inches?

I have ordered a standard 13 / 16 to see what l am supposed to be working towards then go from there.

Does this mean 1/8” outer and 3/32” inner as the listings are in mm not inches?

3 / 32" (2.4mm) refers to the width of the rollers of the required chain which is the same for both sprockets. The thickness dimensions of the sprockets given in the document are measured near the hub -- the smaller outer sprocket will narrow from 3.1mm when approaching the teeth to accommodate the chain.

How do you adjust the 2 speed derailleur?

Mine has stopped shifting down into the smaller cog, the derailleur moves with the shifter, doesnt seem to have micro adjustments like a standard derailleur

If you have the older sticky up lever or a B75, you can open up the lever and the housing has more than one slot it can sit in.

OTOH most problems are caused by dirt in the chain pusher pivot or the jockey wheels.

Make sure it’s mint clean before you do anything else

I've done the 3 speed conversion with the DT swiss shifter on a 2019 Brompton. I wanted more range on the gearing, not just 3 gears, I went to 12 - 15 - 19t.

I just found shimano sprockets which looked right and tried them. I didn't know what I was doing really and could find any info on it. I believe 17t is the spec limit but several people said you can go to 19t with barely any frame rub, possibly 21t if you're prepared to file a mm or two off the frame. I wasn't.

The only surprises were that I needed a thinner circlip and a spacer for the chain tensioner to stop it rubbing.

The shifting is pretty good actually. I got the DT swiss shifter expecting I may have to switch to friction, but it's fine. Just get an inline chain tensioner.

Weirdly the drivetrain is noisy in the mid and high gears. I thought initially it was poor chain alignment, but they should be better aligned than the low gear? Maybe I have the wrong chain length? Maybe the chain tensioner is compromised for this gear range?

There's a thread on this that no one uses BTW: https://www.lfgss.com/conversations/228623/

Sprockets I used:
12t: Shimano CS-5800 Sprocket 12T for 11-28T/11-32T with Built-In Spacer (Design 12T)

19t: https://www.sjscycles.co.uk/cassettes/shimano-ultegra-cs6600-sprocket-19t-1zd-1900e/

I guess I reused the 15 or 16t one that came with the Brompton.

There's a thread on this that no one uses BTW

damn, sorry - when I asked about this I was looking at the minimods kit, and that thread didn't come up in a search for that https://www.lfgss.com/search/?q=minimod+sort:date