All-City Natureboy Eccentric Bottom Bracket: Where Chain Tension Changes
The All-City Natureboy eccentric bottom bracket is a defining part of the documented A.C.E. single-speed build. Its chain-tension adjustment is associated with the crank position, rather than an ordinary rear derailleur. Start with that mechanism when a used example has unfamiliar hardware around the bottom bracket.
All-City Natureboy eccentric bottom bracket in the source
The Japanese Natureboy A.C.E. page describes an eccentric bottom bracket used for chain-tension adjustment. Its frame specification names PF30, while the complete-build row names a PF30 eccentric unit and a SRAM and Shimano spacer kit. These entries describe related but different parts of the assembly.
PF30 is not the complete identity of every part inside the shell. Keep the eccentric description and the actual crank information in the enquiry. Ordering an unspecified PF30 bearing assembly solely because the frame row uses that label leaves the tensioning mechanism and crank interface unresolved.
Understand what changes, without using this as a service procedure
An eccentric arrangement places the crank support off-centre within the surrounding assembly. Changing its position changes where the crank sits relative to the rear wheel. That explains why this system can affect the single-speed chain run without requiring a rear derailleur to take up chain length.
This explanation does not supply the permitted rotation, chain slack or fastening procedure for the actual unit. Those depend on the fitted assembly and its instructions. Have an unfamiliar eccentric identified before loosening it, especially if the bicycle has acquired replacement cranks or hardware.
Keep the original single-speed context visible
The listed complete bicycle has no front or rear derailleur, a 40-tooth crank chainring and an 18-tooth single-speed rear cog with a spacer kit. These details establish the context of that historical build. They do not approve a different chainring, bearing substitute or geared conversion.
For service, collect the eccentric’s markings, crank reference, existing spacers and any previous work record. Ask the workshop which instructions and parts apply to that assembly. The useful result is a correctly identified tensioning system, rather than an attempt to resolve every single-speed symptom by moving the rear wheel.
All-City Natureboy eccentric bottom bracket FAQ
Does the cited Natureboy build have a rear derailleur?
No. Its complete-build listing identifies a single-speed rear cog and no front or rear derailleur.
Does PF30 alone identify the whole replacement?
No. The source separately names the eccentric assembly and spacer kit; the actual crank and installed unit also matter.
Does this article give the chain-tension setting?
No. Obtain the applicable instructions and have the identified eccentric assembly set and checked correctly.
The All-City collection keeps this mechanism reference available beside the separate brand overview.
Primary references: Japan Natureboy A.C.E. complete build (https://ride2rock.jp/products/111273/); dated Natureboy A.C.E. announcement (https://ride2rock.jp/blog/112098/).
Photograph credits and permissions
Photograph 1
Original title: Gazebo off the Northeast Branch Trail
Creator: Mr.TinMD; creator URI: https://www.flickr.com/photos/mr_t_in_dc/
Original source URI: https://www.flickr.com/photos/mr_t_in_dc/50337876153/
License / permission: CC BY 2.0 Generic
License / permission URI: https://creativecommons.org/licenses/by/2.0/
Modification notice: Original photograph retained unchanged.