Hello,

I've retired my Citizen Tokyo,



and just bought a Brompton ML3 in Cobalt, BSR 13T x 50T.



I've added TRP levers, Crank Bros. Candy pedals, Soma Brevet Handlebar, S&A barend shifter, Brooks Swallow saddle and bar tape, and Primo Comets.
I'm looking forward to tinkering with it more in the future.

I have a few questions.
I understand that a 15T is the biggest cog I can fit. The only option I could find is, 15T R sprkt 3/32in, 3-spline 2mm: SRAM 6-spd, will this work?
Any other options for cogs?
If not, I may just go to a 44T chainring.
If I wanted to go to a six speed by adding two cogs in the back, would I need to switch to a 2/6 speed tensioner and do another bar end shifter?

Thanks in advance for any tips...