(d.) Extra Cog for 4 speed or beyond application (SunRace)
1. Older stock tensioner might suffer from deformation and cause it to touching chain on 11t position (you will need some filing or add tensioner washer to correct). Aluminum 3rd party tensioners are stiff enough to void this. 11 speed chain also helps with its narrower profile.
(a.) X3 Unibody Cog Set (MiniMODs)
3 sprockets (11-14-17T) in One Unit. Precision CNC machined
SCM440H heat treated steel. ED-Electrophoresis deposition surface processed black
Most efficient drive output, crispy clear shifting reaction
Plug and play, very easy to install and finetune. Stock components compatible
11 Speed and up (narrower) Chain required. Leading teeth on-shift design for ultra smoothness.
Circlip type for maximum compatibility (1.5mm custom snap ring included).
For 9 spline Shimano spec, compatible with Stock Brompton 2 speed hub (BWR 3x2 6 speed hub) and most third party external cog wheel mods (e.g. MiniMODs, Orz, Hubsmith, Joseph Kuosac, etc. )
Not compatible with Sturmey Archer SRF-5 (W) 5 speed hub or Brompton BSR 3 speed, but compatible with SRF-5(N) 10 (5x2) speed hub, so 5x3 is possible