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The headset is the set of components on a bicycle that provides a rotatable interface between the bicycle fork and the head tube of the bicycle frame itself. The short tube through which the steerer of the fork passes is called the head tube. A typical headset consists of two cups that are pressed into the top and bottom of the headtube. Inside the two cups are bearings which provide a low friction contact between the bearing cup and the steerer. ==Sizes== Traditional bicycle head tubes and headsets are sized for a steerer tube (also known as the fork column). Many frame and fork manufacturers are now building their parts around a steerer tube with a diameter of 1⅛ inch. The larger diameter of the head tube and headset gives added stiffness to the steering portion of the bicycle. Common sizes *1" or 1 inch (25.4 mm). This may have a fork crown (The base of the fork steerer tube) of a number of different dimensions. Milling may be necessary to make some headsets fit. ::26.4 mm (ISO) ::27.0 mm (JIS) ::Other sizes are becoming common, more so all the time.〔 〕 *1.125" or 1⅛ inch (28.575 mm) *1.25" or 1¼ inch (31.75 mm) *1.5" or 1½ inch (38.1 mm), as used in the OnePointFive International Standard. *Cannondale Headshok. Although a Headshok steerer is close to 1.5" it is actually 1.5625" or 1 9/16 inch (39.6875 mm). The Headtube dimensions for 1.5" and Headshok are very similar, differing only in the minimum press depth. * 1.5 inch to 1⅛ inch "tapered" headsets (2009 onwards). The lower bearing is 1.5 inches for increased stiffness and the upper is 1⅛ in for reduced weight and to match existing stem interface. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Headset (bicycle part)」の詳細全文を読む スポンサード リンク
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