Most bicycle

Bicycle

A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

s, tricycle

Tricycle

A tricycle is a three-wheeled vehicle. While tricycles are often associated with the small three-wheeled vehicles used by pre-school-age children, they are also used by adults for a variety of purposes. In the United States and Canada, adult-sized tricycles are used primarily by older persons for...

s and motorcycle

Motorcycle

A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

s have a tubular frame. The front fork (which holds the front wheel) pivots within the head tube . On a motorcycle, the "head tube" is normally called the steering head. On a bicycle the head badge

Head badge

A head badge is a manufacturer's logo affixed to the head tube of a bicycle.Head badges may be made of metal or plastic, and they may be held in place with adhesive, screws, or rivets...

 is invariably mounted on the head tube.

Bearings

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

• In bicycles, these bearings are collectively called the headset
  Headset (bicycle part)
  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...
  
  . These are usually ball bearings, although some headsets use needle bearings
  Needle roller bearing
  A needle roller bearing is a bearing which uses small cylindrical rollers. They are used to reduce friction of a rotating surface.Needle bearings have a large surface area that is in contact with the bearing outer surfaces compared to ball bearings...
  
  .

• In motorcycles, these bearings are also referred to as headset, or steering head bearings or steering neck bearings. These are usually tapered roller bearings.

Castor angle

The steering axis angle, also called castor angle

Caster angle

thumb|250px|θ is the caster angle, the red line is the pivot line, and the grey area is the tire.Caster angle or castor angle is the angular displacement from the vertical axis of the suspension of a steered wheel in a car, bicycle or other vehicle, measured in the longitudinal direction...

, is the angle that the head tube and hence the steering axis makes with the horizontal or vertical, depending on convention. The steering axis is the axis

Rotation

A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

 about which the steering mechanism (fork, handlebars, front wheel, etc.) pivots.

• In bicycles, the steering axis angle is called the head angle and is measured clock-wise from the horizontal when viewed from the right side. A 90° head angle would be vertical. For example, Lemond offers:
• a 2007 Filmore, designed for the track, with a head angle that varies from 72.5° to 74° depending on frame size
• a 2006 Tete de Course, designed for road racing, with a head angle that varies from 71.25° to 74°, depending on frame size.

• In motorcycles, the steering axis angle is called the rake and is measured counter-clock-wise from the vertical when viewed from the right side. A 0° rake would be vertical. For example, Moto Guzzi offers:
• a 2007 Breva V 1100 with a rake of 25°30’ (25 degrees and 30 minutes)
• a 2007 Nevada Classic 750 with a rake of 27.5° (27.5 degrees)

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 the headset

Headset (bicycle part)

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...

standard. For example, frames that take one inch (25.4 mm) 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
1"/25.4 mm	1" JIS	28.8 mm
	1" ISO	30.0 mm
	1" BMX/OPC	32.5 mm
1 1/8"/28.6 mm	1 1/8" standard, threaded and threadless	33.8 mm
	IS 1 1/8" integrated 45x36	41.1 mm
	Campagnolo "Hiddenset" 45x45	41.9 mm
	Zero Stack/ Internal	43.9 mm
1 1/4"/31.75 mm	1 1/4" standard	36.8 mm
1.5"/ 38.1 mm	1.5" standard	49.6 mm

• Motorcycles

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