bike - Stem bicycle part
Photograph by Velo Steveon Flickr.
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 40° 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. The length of the stem determines how far forward of the steerer tube the handlebars are. Quill stems each require a minimum length which must insert into the headset steerer tube, thereby determining a maximum length that may extend above steerer tube. Stems come in at two common nominal sizes: 1 and 1 1/8 . (See: photograph of Star-nut) Newer model forks, with carbon fiber steerer tubes, use an expander plug instead of a star nut, which once installed serves the same purpose as the star nut, but will not damage carbon fiber forks as a starnut will (by design a Star-nut digs into the surrounding tube, which, while safe with aluminum, can weaken carbon fiber to the point of failure) Special adaptors may allow a threaded fork to receive a threadless stem. A threadless stem with a removable face plate on a racing bicycle holding drop handlebars. A stem with a removable face plate holding a moustache handlebar as seen from the top of the bike. Threadless stem with a removable face plate on a mountain bike. Adjustable threadless stem with a removable face plate. Advantage Threadless: Advantage Quill: Stems are often constructed of aluminum, but are also available in steel, titanium, carbon fiber, and carbon fiber over aluminum. Stems tighten around and hold the handlebar either by pinch bolts, which require feeding the handlebar through the stem — after removing controls, accessories and bar covering; or via detachable faceplates, also called pillow blocks, especially on BMX bicycles, Stems normally have two dimensions that affect bicycle fit: an angle and a forward length or extension.
Sometimes called a goose neck, a stem s design belongs to either a quill or threadless system, and each system is compatible with respective headset and fork designs: Somewhat counter-intuitively, the term threadless derives not from whether the stem itself is threaded— but rather from whether a headset lock nut threads on to the fork steer tube. Threadless stems feature a modular design where the stem clamps around the outside of the top of the fork steerer tube that protrudes above the headset. With threadless stems, a star-nut is driven down into the the threadless steerer tube and held in place by two barbed flanges.
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. An elastomer suspension stem. 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 adjustable stem was developed by the famous cyclist, Major Taylor, hence they re sometimes called Major Taylor Outriggers. At one time, some manufacturers (Softride) marketed suspension stems.
The ISO standard for the clamping area of a handlebar is 25.4 mm (1 ), which is used on mountain bikes and many Japanese-made road handlebars. Un-threaded forks often require less labor to swap than threaded. The older of the two handlebar stem styles, quill types have been largely displaced as the industry standard but remain in use on less expensive bikes and higher-end retro bikes.
While there are purported advantages, there are not any standards yet developed, with each manufacturer following its own conventions. The stem is the component on a bicycle that connects the handlebars to the steerer tube of the bicycle fork.
This type of stem may be adjustable in length with one section of tubing telescoping into another. . 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.
Standard brake levers can be used as it is only the stem clamp central section that is oversized. Shims are available to fit a 31.8 mm stem to either a 25.4 mm or 26.0 mm bar, so many new models of stems are oversize-only. Some stems have a hole through the horizontal part to support the front brake cable on bikes with cantilever brakes such as cyclo-cross bicycles and older mountain bikes. Certain uncommon adjustable stems have the handlebar clamp unit mounted on a moveable slide, permitting variable fore and aft settings.
The variations of the 1 standards, when they differ, regarding the other press-fit parts of the head set is 0.2 mm, a small enough difference that it can be safely ignored. 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.
Some quill stems also have other angles, e.g. This is rapidly taking over from the previous mix of sizes, although other accessories such as some light or computer brackets may also need to be oversized to fit the thicker bars.
However, the Italian unofficial standard is 26.0 mm, which is the most common clamp size for road bars. Quill stems may also have a height (above minimum insertion mark).
Manufacturers frequently omit the clamp size from advertising or packaging. BMX bikes usually have a 22.2 mm diameter clamp size. A more recent standard is a 31.8 mm (1.25 ) clamp for both MTB and road bars. The quill stem fits down into the inside of the top of the fork steerer tube to be held in place internally via either a wedge and bolt or cone shaped expander nut and bolt.
The quill stem requires a threaded fork that extends up through the headset but does not protrude beyond the headset. Quill stems showing wedge (on left) and cone-shaped (on right) expander nuts. Quill stem without a removable face plate. Quill stem without a removable face plate. Quill stem with a removable face plate. Adjustable quill stem with a removable face plate. An unusual two-headed quill stem with removable face plates and a hole for the front brake cable. Adjustable quill stem. Classic road quill stem. Quill stem without a removable face plate. Threadless stems, the newer of the two styles, are widely popular, and have displaced quill stems as the industry standard. Tapered steerer tubes: As of 2008 a number of manufacturers of high end road and mountain bikes are coming out with tapered steerer tubes.
Threadless stems require an un-threaded steerer tube — which may vary in length for each bicycle model. Quill systems predate threadless systems. The two common sizes are 26.0 mm 25.4 mm, others exist as nonstandard variants, often found on low end bikes in the United States.
The top cap bolts into, and pulls against, the star-nut preloading the headset bearings. The steerer tubes are then cut to length to fit upon installation.
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. Stems must also be compatible with the dimensions of the components that they connect, namely the handlebar clamp diameter and steerer tube diameter. For road quill stems, the angle is normally 73° which causes the extension of the stem to be nearly parallel with the ground.
With a quill stem, the steerer tube does not protrude above the headset. This makes replacement parts difficult to come by, only available from the original manufacturer. Both quill and threadless stems come in a variety of bicycle handlebar clamp diameters.
Quill stems require a threaded headset — of specific length for each bicycle model.
