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I haven't tried it, but this https://bikegang.ecwid.com/?3vOM2tpoyAUSFIWU-Te2WMunXOCIAUaWhSyxRHLzwBUfmyTqrZ6dOUI9E#!/Brompton-2-to-3-Speed-Sprocket-Cog-Thumb-Shifter-Kit-MiniMODs-x-Sturmey-Archer/p/115439619/category=9803294 looks like a cheap and simple way to try this mod

I didn't realise that this topic had been revived! Good to see other people have taken the ball and are running with it.

I bodged the stock Brompton shifter - see the PDF

OP here. I'm still running the conversion and it's still fine.

I would update the PDF, but I can't find the original document

The major change that I've made since the original is to replace the hacky garden wire circlip with the original Brompton one - you need to file back the inner face of the smallest cog to get it to fit, but I did have problems with the wire coming out and leaving rattling cogs. I wish I could just find a thin-enough circlip of the right diameter - if you do, please let me know.

The shifting is a little temperamental. When the cables get sticky or the jockey wheels clogged I need to throw the shifter from 1st to 3rd rather than trying to go from 2nd, but the convenience of 3 close ratios for my flat commute outweigh the negatives for me.

There is a middle way on the tyres.

I run a Marathon on the back, where I get most punctures and it's a pain and a 15mm spanner to fix, and a Kojak on the front, which I rarely flat, has no chain to manage and can change with an Allen key.

I keep a spare tube in the frame, but with this arrangement haven't had to use it all winter. And while the bike feels sluggish with 2 Marathons, I can't really feel the difference between this arrangement and a pair of Kojaks, which averaged a puncture a fortnight over the summer.

BTW, my height stop on the seat post is lightweight insulating tape :o) I just read the instructions for that really expensive thing on the tat bazaar and improvised - works a treat.

Try this http://bromptontalk.wikispaces.com/Seatpost+Height+Keeper

just doing this to my 2 speed

Let me know how you get on - make sure you read the addendum at http://bromptontalk.wikispaces.com/3+Speed+Cassette

That kit has the new QR included, or you can get it on its own

http://brilliantbikes.co.uk/brompton-folding-detail/453-brompton-seat-pst-clamp-quick-release-5053099040186.html

I've tried using a standard seatpost QR, but frankly, you're better spending the money for the pukka Brompton part. It stays in line instead of hanging down, and the cam action is just right, whereas a standard QR goes from too tight to too loose without ever being perfect.

to give my little 3-speed Brompton a fighting chance at the Smithfield Nocturne!

Used but not too warn would be fine. If it came with its 12 tooth neighbour that would let me run 11, 12, 13 for even more lactic pain...

TIA

Duncan

One of the product designers at Brompton did this to his 4-5 years ago, I think he used 9sp shimano cassette 12/13/14 rings and adapted his 2sp shifter.

Interesting, do you have a link so I can compare notes?

I did find a site in Spanish on the wayback machine with some details of such a conversion - Chrome's auto-translation helped a little...

^this

With 16" wheels that's 52 to 60 inches, so is perfect for commuting

I think more like 62-72 - it's a long flat commute.

Am I missing something?

I have huge calves.

And 16" wheels.

I know that there are some Bromptonites here, so I thought I'd share some progress on a little project to run 3 cogs on a standard Brompton hub.

The essence is to replace the 2 current sprockets with Shimano 10-speed ones. It's letting me run 12,13,14 x 54 which is fantastic for commuting.

I'll upload some images to view inline if anyone is interested, but in the meantime instructions are here.

If anyone tries it please let me know how you get on - I'm interested to see if it works on other bikes, and in particular the BWR hub.

Cheers

I might be interested in the tiring 12 year old model.....

I think 17 years is the age at which that doesn't sound just creepy!

If you we're serious, my son has first refusal, but I'll bear it in mind.

Do they also supply the rest of the wheels or are you forced to roll on those hubs directly?

:-)

The only one I like so far is the Strida, but I heard it's a pain to ride.

You heard right. It really isn't a bike for anyone but a masochist with a 5 minute ride to the station.

got a spare ti brompton going if anyone is interested, 2008/2009 s2l-x with blue titanium post, 2 choices of levers, brooks B17, ergon grips marathon tyres but standard otherwise

ridden a grand total of 100 miles in 4 years i would say but i'm kidding myself that the mrs will ever give a crap and we've just bought a house so need the cash to knock walls
think the going used rate is about £1000 (1200+ on ebay) - anyone interested?

Is this still available? My 12 year old model is tiring and I need a replacement...