MIniMODs
MiniMODs X4 Unibody Cog Set for Brompton Bicycle
MiniMODs X4 Unibody Cog Set for Brompton Bicycle
Weight: 59g
Gear Range: 11 / 13 / 17 / 21T
Features:
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CNC-machined unibody with 4 integrated cogs: 11–13–17–21T
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Made from SCM440H heat-treated steel with ED (Electrophoresis Deposition) black surface finish
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Delivers highly efficient power transfer and crisp, precise shifting
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9-spline Shimano spec: Compatible with 2/6-speed Brompton (C Line and Electric B with BWR hub) wheelsets
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Requires 3rd-party longer tensioner arm and derailleur chain pusher for proper function
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Compatible with most 3rd-party 2-speed rear hubs (MiniMODs, Hubsmith, H&H, Andoza, Joseph Kuosac, ORZ, RIDEA, Suncord) — supports both circlip snap ring and lock nut types
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Includes custom 1.5mm and 1.8mm MiniMODs circlip snap rings
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Compatible with 10-speed and up (narrower) chains
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Features on-shift leading teeth design for ultra-smooth transitions
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Not compatible with Sturmey Archer SRF-5(W) or Brompton BSR 3-speed hubs
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Compatible with SRF-5(N) 10-speed (5×2), allowing up to 5×3-speed builds
Note:
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Older Brompton stock tensioners only support up to 19T — you will need a 3rd-party tensioner (e.g. aluminum)
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Tested with:
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MiniMODs, H&H, BooK, DCCH, Thx4Ride parallelogram derailleur systems
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Suncord and RIDEA chain pusher-type derailleur systems
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Additional required (not included):
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4-speed thumb shifter (Brompton stock style recommended)
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10-speed or higher chain
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Disclaimer:
The X4 Unibody Cog Set is based on our popular X3 Unibody Cog Set, which allows for an easy 2-speed to 3-speed DIY upgrade using mostly stock components.
However, the 4-speed modification requires additional 3rd-party components and greater setup precision.
Due to inconsistent tolerances on Brompton rear triangles (manually manufactured), compatibility and setup may vary.
We recommend professional installation at an authorized MiniMODs dealer.
Only order directly if no dealer is available near you and you are confident in your mechanical skills.