BromptonINrio

my friend, im afraid to say you pick a wrong bike to play light.
the way to lightwheight a brompton is at hand, the singlespeed one plus all carbon/titanium at a cost of few thousand dollars.
the lighest i see was 7.4kg

nachy

So, in terms of efficiency/usability/price/weight, everybody think an internal gear hub is the best option, right?
I'v dowloaded for 1 pound the "A to B" magazine where there's an article from Derek Cranage and his lightweight brompton 7,3kg, it's really interesting. He bought a lot of his accessories from china at Aliexpress and he gives references. I might follow some of his advices.

Chagzuki, would you have a link about the 4 speeds mod?
And if I would decide to do a single speed. Would you have any advice about the number of teeth for the front and the crankset chainrig? I mean the good ratio? 50t and 12 or 13 teeth in the rear?
I've got an idea...Let me know what you think...
What about a single sprocket and a crankset with two chainrings, that would be 2 speeds, it would allow a very lightweight rear wheel and the possibitly to ride in a hill with the small chainring?
I think a front derailleur is easy to install and lightweight. No complicated modification.

BromptonINrio

if you choose singlespeed path simply dont worry about ratio because correct gear ration in singlespeed is an non exist thing.You will always be in wrong gear.
About two chainrings on front, many people do put then and manual shift though cranks.
To add an front derrailer isnt hard but the hard in the matter is that the front derrailer will be push very hard by chain while fold and this lever moviment does have habiliti to break your derrailer cage.

chagzuki

chagzuki

nachy

You completely right!
But I guess it is possible to find an average set up.
We should look for someone who has already make a modification on his bike. He could say: it doesn't work or try this, I failed on that, blablabla

nachy

That's wonderful chagzuki!
but it seems it's not released yet, and it's probably going to be very expensive.
The good thing with Derek Cranage, he tells where he found all its gears and actually it is common gears that you can find almost everywhere.
I dream about something like that for the brompton, a modification but very simple, easy, and with materials or gears we can find easily.
Today, I ended up to do the sturmey archer internal three gears hub maintenance, I was a bit afraid, but everything was fine. And now it works perfectly, but it's still too muuuuuuuuuuuuch heavvvvvvvvyyyyyy!

berlinonaut

I do not see a real advantage in comparison to the stock 2-speed Brompton with your idea. The two speed has 54/12-16, the single speed has 54/12. If you would like to achieve the same effects with two chainrings that you have with the 2-speed you'd i.e. need a 54t and a 40t chainring. Together with the derailleur this will probably be more expensive and heavier than the factory 2-speed plus you will run into issues when you try to fold the bike in lower gear. Also, shifting on the chainwheel will take longer than shifting on the sprockets (as you need the chainwheel respectively the sprocket to turn at least 1/3rd for the shifting to take effect and this takes longer on the chainwheel than on the sprocket).
What is more common is to add an additional chainwheel to the 2-speed to achieve a "granny gear" for those moments when you need it on the hills. As in this setup the smaller chainwheel is only used very occasionally many people to not use a front derailleur an downshift by foot and upshift by hand.

So depending on what you want to achieve it may be possible but more complicated, more expensive and heavier than the factory 2-speed and at the same time less convenient.

fietsbob

I Have one of those FD adapter mounts , I got from CM Wasson,
the original US Brompton Dealer, now retired. I'm not going to use

Will sell ... send a PM.. (US sales )..