Brompton gear mods

I have an idea for getting light 3-speed on a Brompton: using 3 9 speed cogs on a shimano freehub (bodged to get into the 115mm OLD dropouts) and the Brompton derailleur with a different shifter to widen it’s reach.

Any thoughts…or what’s a good Brompton forum to discuss?

Been there, done that 😉

Biggest problem is that normal derailleurs – even long-cage ones – don’t have enough pull to stop the chain going slack when you fold. You can bodge it with a wire loop thing like on the Birdys though.

Why do 3-speed, though? The 2-speed works well if you want light and simple. I was doing it to get 8 speeds.

Edit: Ignore – must read better. Will there be enough travel on the carriage? It’s pretty much at the limits with two cogs.

might be possible with 10speed sprockets and chain perhaps on the brompton freehub?

I like the 2 speed as it is only change I made was a 52 front rather than a 54. though I also have an inner 38 (manual shift in case of proper hills)

Ben – dunno, I’d need 10.5mm vs 7.5mm from what I can see. I did wonder if some modification to the jockey wheel/shifter cage might be needed. I guess I thought it might have been tried already…could this be a cynic-al first?

I am thinking of a shimano freehub to get an 11-19T – should be enough range, I’m also now thinking of a double up front with a f. mech with the bottom split.

Yeah it might be crap, I just like dicking around like this…also it may be a nice light compromise, 2-speed just won’t be enough.

So what’s the best Brompton forum?

Hmm – you can increase the travel on the jockey wheels by fitting a slightly longer spacer – I’ve also done it using PCB standoffs. Metal ones of course 😉

To increase the carriage travel, not sure – maybe file off the metal wing-shaped wotsit a bit so the limit screws have further to go – you might also have to alter the plastic arm a bit where it passes the chainstay.

19t will require a mod to the chainstay to clear.

Al, have you measured to see if you can get 3 10 / 11 speed sprockets oon the brompton freehub? it is shimano pattern, loose the spoke protect and then loose the circlip system. not sure if the brompton system has sprockets has 8 or 9 speed sproket spacing, if it is 8 then going to 10 speed will give you quite a bit if space – will measure the spacing on mine.

other option might be worth a look is perhaps something like a Hope Trails hub more room for spockets and per the OLN could be reduced to suit the brompton

I have a double on the front of my bike, don’t use a shifter though, shift down by knocking the chain off woth foot and then reaching down to lift the chain back on.

if you wnat that range you woukd be better going for a nexus/alfine conversion or using the brompton 6 speed system.

Or a Rohloff 😉