Stem
The stem is a component of the bicycle . It connects the handlebars with the fork .
Designs
Classic inside clamping
In the past, only stems with an expanding cone or angled cone (actually an obliquely cut cylinder) were used, which are inserted into the fork shaft. You have the advantage that the height of the handlebars can be infinitely adjusted and the stem can be dismantled without loosening the headset. For a long time, stems with countersunk screws were required in the professional sector, because the risk of injury to the chest is lower. This rule has been deleted since the advent of the aheadset tax rates.
When a new fork is mounted for the first time, the thread is shortened to the length specified by the frame's head tube.
Installation
Stems or handlebars usually have a design-related minimum length that is marked on the tube and up to which they have to be pushed into the steerer tube.
Safety risk in the event of incorrect assembly
This marking on the tube may only be seen when the handlebar stem is removed, otherwise the stem of the stem is clamped too short. There is then the risk that the leverage forces ( bending ) overload the material of the pipe. In the long run, fatigue fractures can occur - with the risk of a serious fall.
If there is no marking on the stem, it can be roughly assumed that 65 mm of the handlebar stem must be clamped in the steering bearing or steerer tube.
If the handlebars are to be set higher than intended on the stem, a longer or stronger stem or a bicycle frame with a longer head tube must be selected.
Ahead stems
In the 1950s, stems were developed that encompass the steerer tube from the outside and are clamped by screws. In this case, the steerer tube does not need an external thread . Either the clamped stem or the spacer sleeves placed underneath serve as a stop for the upper headset bearing .
To adjust, the clamping screws of the stem are loosened a little. Then the stem can be turned sideways or the number or height of the spacer sleeves can be adjusted. Before tightening the clamp, the adjusting screw in the center of the steerer tube is slightly tightened. It determines the form with which the tax rate stores are drawn together.
If the steerer tube itself does not have an internal thread, a special claw is pushed into it, which expands in the shaft and has an internal thread to accommodate the long adjusting screw. If you want to be sure that the claw is inserted slowly into the steerer tube without tilting, it can be pulled into the steerer tube from below using a longer threaded rod, a large washer and a nut . Otherwise it is often hit from above.
A slight height adjustment by removing, adding or exchanging spacer sleeves is easily possible, provided the length of the steerer tube allows this. If the steerer tube is too short, a stem of a different length or a different angle of inclination can be used. Special adapters or spacers are also available to lengthen the shaft.
As a rule, the shaft of a new fork is shortened to the length corresponding to the desired handlebar height. Theoretically, the shaft can be left in its full length in order to obtain the full adjustment option. In this case, spacer sleeves usually have to be pushed on above the clamped stem so that the headset can be tightened using the central adjusting screw. This setting can only be made on the upper part of the control bearing itself with special designs. There is an increased risk of injury if you fall on the handlebars if the uncut shaft protrudes beyond the stem.
Direct mount stems
This stem has become the standard on downhill mountain bikes due to its reliability and greater resilience. The stem is either attached to the upper bridge of the double bridge suspension fork or is already integrated into the bridge. It has no connection to the steerer tube.
material
In the past, stems were made of steel. The vast majority now consists of cast aluminum . High quality stems are made from cold forged aluminum alloys. Stems made of steel are usually only used on very cheap bicycles.
Parameters
There are four important dimensions when choosing a traditional or an ahead stem:
- Steerer tube diameter,
- Diameter of the handlebar clamp,
- Shaft length or and
- Angle or height.
Diameter of the steerer tube
For shaft stems, the inside diameter of the fork is decisive, which is traditionally based on the inch (one inch corresponds to 25.4 mm). The previously prevailing dimension was 22.2 mm ( 7 ⁄ 8 inches), today 25.4 mm (1 inch) is sometimes used. Less common is 28.6 mm ( 1 1 ⁄ 8 inch).
Usually the material thickness of the two walls of the pipe together is 1 ⁄ 8 inches thick, so that with the above-mentioned inside diameters, the outside dimensions are 25.4 mm (1 inch), 28.6 mm ( 1 1 ⁄ 8 inches) and 31.8 mm ( 1 1 ⁄ 4 inches), which are provided with a fine pipe thread for the control bearing. It is often unclear whether a “1 inch fork” means the inside diameter for the stem or the outside diameter of the steerer tube on which the headset has to fit.
In the case of Ahead stems, the connection dimension is determined by the (threadless) outer diameter of the steerer tube. Here the standard of 1 1 ⁄ 8 inches (28.6 mm) has prevailed, occasionally 1 1 ⁄ 2 inches (38.1 mm) or 1 1 ⁄ 4 inches (31.8 mm) with increased loads. The previous 1 inch (25.4 mm) dimension is no longer common. Also widespread are tapered fork shafts with a diameter of 1 1 ⁄ 2 inches at the bottom and 1 1 ⁄ 8 inches at the top .
Handlebar clamp diameter
The diameter of the handlebar in the area of the stem clamp is mostly 25.4 mm (MTB), 26.0 mm (racing bike) or 31.8 mm or 35.0 mm (oversize size, for MTB and racing bike). In the past, handlebars also had a diameter of 20 or 22.2 mm. There are only classic stems with internal clamping. Other diameters are rare.
Length and angle
The stem length is the measure from the center of the handlebar clamp to the center of the steerer tube. The stem angle influences the height of the handlebar. A 0 ° stem is at right angles to the steerer tube or head tube and therefore points slightly upwards (since the steerer tube itself is typically at an angle between 70 ° and 75 ° to the vertical). In the case of classic inner clamp stems, the forward-facing part usually points downwards at an angle. Most Ahead stems can be turned around so that they can be used for two different height handlebar positions. Common angles are 6 ° and 17 °.
The length of the stem and the height of the handlebars should be tailored to the area of use of the bike and the height of the rider, especially the length of the upper body and arms. A short stem improves control of the bike, which is relevant for downhill and single trail rides , among other things . The more upright sitting position also provides a better overview in traffic. An even more upright sitting position can be achieved with an upward angled stem.
A long, downward-facing stem, on the other hand, results in a forward seated position and improves aerodynamics. Therefore, this form is particularly found on time trial bikes.
In cycling, the height of the handlebars is often assessed in relation to the saddle. The difference between the height of the upper edge of the saddle and the handlebar tube is referred to as the "cant". If the saddle is higher than the handlebars, it is called “saddle elevation”, otherwise it is called “handlebar elevation”.
If you have to climb many inclines while standing, it is recommended that you first determine the position of the handlebars so that you can do this in a comfortable posture. If necessary, handlebar end grips or a differently shaped handlebar can also be fitted for this purpose. In a second step, the position of the saddle must be adjusted so that it is possible to ride in a relaxed and persistent manner while sitting.
Adjustable stems
There are stems that are adjustable in angle or length. This is how the right handlebar position can be determined. Some stems can be adjusted without tools, which is particularly useful when a bike is used by several people.
literature
- Michael Gressmann, Franz Beck, Rüdiger Bellersheim: specialist knowledge of bicycle technology. 1st edition. Verlag Europa-Lehrmittel, Haan-Gruiten 2006, ISBN 3-8085-2291-7 .
- Fritz Winkler, Siegfried Rauch: Bicycle technology repair, construction, production. 10th edition. BVA Bielefelder Verlagsanstalt, Bielefeld 1999, ISBN 3-87073-131-1 .
Individual evidence
- ↑ Compare to this section: van der Plas, Rob: Das Fahrrad - Technik - Maintenance - Reparatur, Ravensburger Buchverlag Otto Maier GmbH 1989, ISBN 3-473-42564-8 , p. 136.
- ^ Wiener Mechanikerräder 1930–1980: A tour of more than 100 Viennese bicycle brands, ISBN 978-3-85119-342-8 , p. 168.
- ↑ Dimensions of stems on fahrradmonteur.de
