Stem (bicycle part)

Stem (bicycle part)

The stem, also called a goose neck, [cite web
url = http://www.sheldonbrown.com/gloss_g.html#gooseneck
title = Sheldon Brown Glossary: Goose Neck
accessdate = 2008-01-01|last=Brown |first=Sheldon |authorlink=Sheldon Brown (bicycle mechanic) |publisher=Sheldon Brown
] is the component on a bicycle that connects the handlebars to the steer tube of a bicycle fork. Depending on the type of headset the stem either clamps around the steer tube or inserts into the steer tube and is held into place with a wedge. This latter style is referred to as a "quill stem".

Varieties

Stems come in several varieties to suit different uses.

Quill

An older style, still in use on less-expensive new bikes and bikes from specialty manufacturers for track use, has a part called the quill, that fits into the inside of the top of the fork steer tube and clamps it internally in place with either a wedge and bolt or cone shaped expander nut and bolt. [ cite web
url = http://www.sheldonbrown.com/gloss_w.html#wedgebolt
title = Sheldon Brown Glossary: Wedge bolt
accessdate = 2008-01-24|last=Brown |first=Sheldon |authorlink=Sheldon Brown (bicycle mechanic) |publisher=Sheldon Brown
] The steer tube does not protrude above the headset.

Threadless

A newer style, used almost exclusively on all but the least-expensive new bikes (with the notable exception of "track" or "fixed-gear" bikes, on which the threaded style remains popular), clamps around the outside of the top of the fork steerer tube (or quill to threadless adapter) that protrudes above the headset.

Suspension

At one time, some manufacturers (Softride) marketed suspension stems. Softride's stem allowed for up to 3 inches of travel, used a parallelogram linkage, and used a polymer bushing and a steel coil spring for shock absorption. [cite web
url = http://www.bikepro.com/products/stems/soft.html
title = SoftRide Stems: SOFTRIDE ALUMINUM SUSPENSION STEM
accessdate = 2007-04-20
]

Tandem Stoker

The stem for the stoker (rear rider) on a tandem is similar to a stem for a threadless fork and headset, but clamps on the captain's (front rider's) seatpost. This type of stem may be adjustable in length with one section of tubing telescoping into another.

Dimensions

Stems normally have two "dimensions" that affect bicycle fit: an angle and a length (extension). Quill stems may also have a height (above minimum insertion mark). Stems must also be compatible with the dimensions of the components that they connect, namely the handlebar clamp diameter and steer tube diameter.

Angle

For road quill stems, the angle is normally 73° which causes the extension of the stem to be nearly parallel with the ground. Some quill stems also have other angles, e.g. 90°, which results in the stem pointing forwards and upwards.

Newer style stems for threadless headsets come in a wide variety of angles from 0° to 17° and can be flip-flopped, or inverted so that the angle is up or down.

There are also models of quill and threadless stems with adjustable angles.

Length

The length of the stem determines how far forward of the steer tube the handlebars are.

Minimum insertion height (quill stem)

Quill stems also have a maximum length that they can extend upward out of the steer tube.

Steerer tube diameter

Quill stems come in at least two sizes for 1" and 1 1/8" steerer tubes.

Threadless stems come in sizes for 1", 1 1/8", and even 1 1/4" steerer tubes.

Handle bar diameter

Both quill and threadless stems come in a variety of bicycle handlebar clamp diameters. The ISO standard for the clamping area of a handlebar is 25.4 mm (1"), which is used on the majority of mountain bikes and many Japanese-made road handlebars. However, the Italian unofficial standard is 26.0 mm, which is the most common clamp size for road bars. There are also intermediate sizes such as 25.8 mm to try and achieve compatibility with either an ISO or Italian stem, and the old Cinelli-specific size of 26.4 mm. In practice, many modern stems with removable faceplates allow for slight differences in handlebar clamp diameter, but the older type of stem with a single pinch bolt must be accurately matched. In the days of quill stems, a road stem was clearly identifiable from its "7" shape, but nowadays it can be hard to tell the difference between a "road" (26.0 mm) and "MTB" (25.4 mm) stem. Manufacturers frequently omit the clamp size from advertising or packaging.

BMX bikes usually have a 22.2 mm diameter clamp size.

A new emerging standard is an oversize 31.8 mm (1.25") clamp for both MTB and road bars. This is rapidly taking over from the previous mix of sizes, although other accessories such as some light or computer brackets also need to be oversized to fit the thicker bars (some brackets are adjustable). Standard brake levers can be used as it is only the central section that is oversized. Shims are available to fit a 31.8mm stem to either a 25.4mm or 26.0mm bar, so many new models of stems are oversize-only.

On older quill stems, the handlebars are inserted through the clamp hole and secured with a single bolt. On newer stems, two or four bolts and a separate plate hold the handlebars in place, allowing the handlebars to be removed without having to remove the brake levers.

Construction

Materials

Stems are often constructed of aluminum, but are also available in steel, titanium, carbon fiber, and carbon fiber over aluminum.

Attachments

Some stems have a hole through the horizontal part to support the front brake cable on bikes with cantilever brakes such as mountain bikes and cyclo-cross bicycles.

References

See also

*Bicycle fork
*Handlebar

External links

* [http://www.sheldonbrown.com/handsup.html Hands Up! Adjusting Handlebar Height] by Sheldon Brown


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