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To address the changing landscape of bicycle headsets, a group of leading headset manufacturers have collaborated to develop a standardized “language” for headset fitment.
The new Standardized Headset Identification System (S.H.I.S.) creates a common language for describing modern bicycle headsets. The system provides comprehensive and scalable headset fitment information in a standard format; making it easier to communicate headset requirements based on frame and fork interfaces.
The system addresses the four critical interface dimensions required to fit a fork to a frame, as well as bearing location/cup type. To determine fit, four dimensions are needed: stem-clamp diameter, top head-tube inside diameter, crown-race seat diameter and bottom head-tube inside diameter. There are also three common bearing locations;
* EC (External Cup), featuring bearings contained within cups that are located outside of the frame.
* ZS (ZeroStack), featuring bearings contained within pressed-in cups where the cup and bearings rest inside the frame.
* IS (Integrated), featuring bearings that fit directly into a bonded or machined interface that is integrated into the frame.
The Standardized Headset Identification System also makes it easier for bicycle manufacturers, distributors and dealers to demonstrate to customers the different fit options available to them based on a specific bicycles head-tube.
The acronyms EC, ZS and IS have been adopted to indicate bearing location and cup style, and are meant to describe the profile of a headset. Steerer tube dimensions are indicated by a slash mark, and top and bottom measurements are separated by a vertical bar.
EC34/28.6 I EC34/30 would indicate a “traditional” 1-1/8” headset with a straight steerer tube:
Top: External Cup, 34mm Frame ID, 28.6mm Stem-Clamp Diameter
Bottom: External Cup, 34mm Frame ID, 30mm Crown-Race Seat Diameter
ZS44/28.6 I ZS44/30 indicates a 1-1/8” “ZeroStack” or “semi-integrated” headset with press-in cups and a straight steerer tube:
Top: ZeroStack Cup, 44mm Frame ID, 28.6mm Stem-Clamp Diameter
Bottom: ZeroStack Cup, 44mm Frame ID, 30mm Crown Race Seat Diameter
IS41/28.6 I IS52/40 indicates a tapered “integrated” 1-1/8” top mated to an “integrated 1.5” bottom with a tapered steerer tube:
Top: Integrated, 41mm Frame ID, 28.6mm Stem-Clamp Diameter
Bottom: Integrated, 52mm Frame ID, 40mm Crown Race Seat Diameter
ParkTools talk SHIS
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