Head tube

A bicycle head tube with a partially installed bicycle headset; the locknut has yet to be fitted onto the fork steerer tube.

Thehead tubeis the part of a cycle's tubular frame within which the frontfork steerer tubeis mounted.On a motorcycle, the "head tube" is normally called thesteering head.On bicycles the manufacturer's brand located on the head tube is known as ahead badge.

Bearings

The head tube holds the bearings which allow the front fork steerer tube to pivot freely.

• Inbicycles,these bearings are collectively called theheadset.These are usuallyball bearings,although some headsets useneedle bearings.

• Inmotorcycles,these bearings are also referred to as headset, orsteering head bearingsorsteering neck bearings.These are usuallytapered roller bearings.

Caster angle

Thesteering axis angle,also calledcaster angle,is the angle that the head tube and hence the steering axis makes with the horizontal or vertical, depending on convention. Thesteering axisis theaxisabout which the steering mechanism (fork, handlebars, front wheel, etc.) pivots.

• Inbicycles,the steering axis angle is called thehead angleand is measured clock-wise from the horizontal when viewed from the right side. A 90° head angle would be vertical. Some examples of caster angles are:
  • 72.5° to 74° on thetrack bicycle2007 Lemond Filmore, designed for the track (angle varies depending on frame size)
  • 71.25° to 74° on theroad bicycle2006 Lemond Tete de Course, designed for road racing (angle varies depending on frame size)
• Inmotorcycles,the steering axis angle is called therakeand is measured counter-clock-wise from the vertical when viewed from the right side. A 0° rake would be vertical. Some examples of caster angles are:
  • 25.5 degrees on thestreetfighter2007 Moto Guzzi Breva V 1100
  • 27.5 degrees on thecruiser2007 Moto Guzzi Nevada Classic 750

Head tube diameters

Head tubes can use one of several size standards

• Bicycles

The head tube of a bicycle is sometimes designated by the fork steerer column it accepts. This can lead to confusion, since head tube inside diameters are dependent on theheadsetstandard. For example, frames that take 25.4 mm (1 in) steerer columns can have three different inside diameters for threaded and threadless headsets (not including integrated-type headsets). The wide variety of integrated and non-standard, proprietary headsets that some frame manufacturers have created (and abandoned in some cases) makes listing all current and past head tube dimensions problematic. The following table includes the most common sizes; nominal head tube diameters are assuming a 0.1-0.2 mm interference fit, which is what most head tube reaming cutters are designed to bore. Adequate press fits are typically between 0.1 and 0.25 mm of interference.

Steerer column nominal OD	Headset standard	Head tube nominal ID
25.4 mm (1″)	1″ JIS	28.8 mm
	1″ ISO	30.0 mm
	1″ BMX/OPC	32.5 mm
28.6 mm (11⁄8″)	11⁄8″ standard, threaded and threadless	33.8 mm
	IS 11⁄8″ integrated 45°×36°	41.1 mm
	Campagnolo "Hiddenset" 45°×45°	41.9 mm
	Zero Stack/ Internal	43.9 mm
31.75 mm (11⁄4″)	11⁄4″ standard	36.8 mm
38.1 mm (1.5″)	38.1 mm standard	49.6 mm

• Motorcycles

Standard motorcycle head tubes and headsets are sized for a 25.4 mm (1 in) diameter fork steerer tube.

See also

• Bicycle fork
• Bicycle frame
• Motorcycle fork