- Head tube
vehicleframes, most commonly of a bicycleor motorcycle[cite web
url = http://www.chopper-kit.co.uk/ame-chopper-kit-installation.htm
title = Chopper kit installation Guide
accessdate = 2007-04-11] , the head tube is the outer tube within which the steer tube pivots.
head badgeof a bicycle is mounted on the head tube.
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. These are usually ball bearings, although some headsets use needle bearings. [cite web
url = http://www.stronglight.com/stronglight/page.php?nom=produits&keySousFamille=filetageRoute
title = Stronglight Bicycle Components JD A9 Threaded Headset with Needle Bearings
accessdate = 2007-04-11]
In motorcycles, these bearings are also referred to as "steering head bearings" [cite web
url = http://www.motorcyclecruiser.com/tech/service_steering_head_bearings/
title = Motorcycle Cruiser How to Service Motorcycle Steering-Head Bearings
accessdate = 2007-04-11] or "steering neck bearings". [cite web
url = http://www.visi.com/~dalebor/maint.htm
title = Motorcycle Maintenance
accessdate = 2007-04-11] These are usually tapered roller bearings.
The steering axis angle, also called
caster angle, 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 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 [cite web
title = Lemond Racing Cycles
year = 2006
url = http://www.lemondbikes.com/
accessdate = 2006-08-08] 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 [cite web
title = Moto Guzzi USA
year = 2006
url = http://www.motoguzzi-us.com
accessdate = 2006-12-11] 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 tubes can use one of several size standards
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
headsetstandard. For example, frames that take 1" 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.
Traditional motorcycle head tubes and headsets are sized for a 1 inch diameter fork steerer tube.
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