Headset (bicycle Part) - Sizes

Sizes

Traditional bicycle head tubes and headsets are sized for a 1-inch-diameter (25 mm) 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.

26.4mm (ISO)

27.0mm (JIS)

Other sizes are uncommon, but do exist.

• 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.