Stem (bicycle part)
The porch is a component of the bicycle. It connects the handlebars to the fork.
- 3.1 diameter steerer
- 3.2 diameter of the handlebar
- 3.3 length
- 3.4 angle / height
Designs
Classical internal clamp
Previously only found Stems with spreading cone or conical tubing using that plug into the steerer. They have the advantage that the height of the handlebar can be adjusted continuously and the stem can be removed without removing the headset. In the professional area have long been prescribed Stems with inset screw, because in these the risk of injury of the thorax is less. Since the advent Aheadset tax rates, this provision was deleted without replacement, at the urging of the industry.
Installation method
Stems or Lenkerschäfte usually have a design-related, marked on the minimum pipe length with which they clamped inserted in the fork steerer (fitted) must be. This mark may therefore be seen only with removed stem.
Security risk in incorrect assembly
Is the mark to see when installed, the stem / handlebar stem is clamped too short. Even among drivers with " normal weight " then the lever forces (bending ) is too large; the material of the tube is overloaded, is tiring and can break off just above the tax warehouse - with the risk of a serious fall.
Missing the mark on the stem, so you can roughly assume that at least 65 mm of the handlebar stem in the steerer ( hidden in the head tube ) must be clamped.
If you want the link set (if kids want to ride for the kids bike be too big or adults with great body length " normal" bikes) is strongly recommended, not just "put up " just by pulling the handlebar stem. You can remedy in these cases only by another, according to running longer and stronger stem - or better yet by another bike with a larger frame size ( more upright ).
" Aheadset " Stems
Originally designed for mountain bikes " Aheadset " stems have been developed that include outside the steerer tube and clamped by screws. Put a steerer without external thread forward and at the same the stop collar of the upper headset bearing dar. The tax rate is adjusted at a slightly loosened stem by a set screw, which is screwed into a pressed into the steerer claw. The height adjustment of the handlebar is cumbersome and restricted than in Shaft and can be reached only with a correspondingly long steerer distance tubes. At a short shaft must be mounted between pieces for a subsequent more upright sitting position or the stem form itself be changed.
This type of Stems requires less correct operation is possible without any special tools, a cutting of the fork at initial assembly is not necessary. However, a detailed accurate setting of the bike is no longer possible, since the vertical adjustment is no longer infinitely.
" Direct Mount " Stems
This stem is standard for downhill mountain bikes nowadays. The porch will only fit double bridge forks, since he has no contact with the steerer, but is either screwed on the upper bridge, or the bridge is already included in series, ie, bridge and stem are a part.
Advantage of this design is the higher load capacity. Moreover there is no risk that the stem due to the high forces triggers.
Material
Standard are steel or cast aluminum. High quality Stems are made of cold-forged aluminum alloys. Stems made of steel are generally equipped with only very cheap bikes.
Parameters
There are four parameters for a Stem: diameter of the steerer tube, the diameter of the handlebar clamp, length and angle / height.
Diameter steerer
Shaft with the inner diameter of the fork is relevant, which is due to the traditional inch sizes (25.4 mm). There are in addition to the prevailing classical measure 22.2 mm (7 /8 inch) partly sizes of 25.4 (1 inch) and 28.6 mm ( 1 1/8 inches). Usually, the tube walls are added together 1/8 inch thick, so that when the said inner diameters, the outer dimensions 25.4 (1 inch), 28.6 ( 1 1/8 inch) and 31.8 mm ( 1 1/4 inches) form, which are provided with an appropriate pipe thread for the headset. This often arises in practice confusion whether is meant, for example, with a "1 - inch open-end " of the inner diameter of the stem shaft or the outer diameter of the tax warehouse.
In Ahead stems on mounting the other hand, is formed by the ( unthreaded ) outer diameter of the steerer tube. Here the standard 1 1/ 8 inch ( 28.6 mm) has prevailed, sometimes 1 1/2 inch ( 38.1 mm ) or 1 1/4 inch ( 31.8 mm) at an elevated load. The former measure 1 inch ( 25.4 mm) is no longer used. Spreads are also tapered steerer, the bottom 1 1/ 4 inches and above have 1 1/8 inch in diameter.
Diameter of the handlebar
For most types of bicycle handlebars, the center has a diameter of 25.4 mm, but come to increase the stability and current diameter of 31.8 mm are used. One speaks in this case of oversize handlebars (abbreviated OS). In racing wheels slightly different dimensions, such as 25.8 or 26.0 mm are common, which require the exact matching Stems during assembly.
Length
The stem length is the measurement from the center of the handlebar clamp directly to the center of the steerer tube and therefore independent of the stem angle. You should be matched to the application area of the bike and the body size of the cyclist. The stem length also affects the steering characteristics of the bike:
A short stem has the following properties:
- Agile, Mobile and steering
- Simply lifting the front wheel possible.
Such is therefore preferably used in downhill and singletrack riding in mountain bikes; a long stem on the other hand usually for touring and cross-country wheels.
Angle / height
The stem angle affects the height of the handlebar. A 0 degree stem is perpendicular to the steerer and has therefore slightly upward. Many angled Aheadset Stems can be mounted to the longitudinal axis rotated so that two different handlebar heights can be selected.
In bicycle racing the height of the handlebar is generally measured in relation to the saddle. The difference between the height of the upper edge of the saddle and the handlebar stem is referred to as " camber ". If the saddle is higher than the handlebars, it is called "saddle elevation ", or of "handlebars cant ".
Most common are at an angle adjustable stems. Although these are heavier and theoretically less stable than other stems but allow a more precise adjustment of the handlebar positions. Your adjustment is usually done with the help tool and is not intended to adapt a wheel to different users or the sitting posture to change often. For such a purpose, there are special tools adjustable stems.