Seat post
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In a bicycle or moped , the seat post is a tube that connects the saddle to the frame . The height of the saddle can be adjusted thanks to its telescopic displaceability in the saddle tube.
Modern CFK -Sattelstützen weigh partly below 100 g, aluminum support conventional length between 200 and 300 g, those made of steel g to about 500th
Fixation in the frame
The seat post is inserted into the saddle or seat tube of the bicycle frame and clamped in place. The seat tube is slit a few centimeters at the back. The outside diameter of the seat post and the inside diameter of the seat tube must match. 25.4 mm (1 inch) for simple city bikes, 27.2 mm for other and racing bikes and 31.6 mm for mountain bikes are common . But there are numerous other dimensions in increments of 0.2 mm.
A saddle clamp at the upper end of the seat tube is used to fix it in the seat tube. The clamp is either integrated in the saddle sleeve or placed as a ring around the end of the seat tube. The clamping ring can also be firmly connected to the seat tube. The clamp is clamped either by a screw with nut or threaded sleeve (with a collar as a stop) or by a quick release with a clamping lever.
Mountain bikes usually have a clamp with a quick release so that you can lower the saddle on steep slopes and thus shift your body further back, which reduces the risk of falling over the handlebars. Today there are also seat posts that can be lowered and raised again at the push of a button. A disadvantage of the quick release is that the seat post and saddle can easily be stolen. Tensioning screws with specially shaped heads are also offered for theft protection. Otherwise, we recommend securing high-quality saddles or seat posts on the frame, for example with a light spiral lock or a steel cable.
Traditional design "saddle candle"
Until the 1990s, the only design was a simple tube made of steel or aluminum with a standard upper taper to 22 mm to accommodate the saddle block . This consists of a clamp to connect the tapered tube to the inner rails of the saddle. The clamp is also used to adjust the saddle angle. To distinguish it from the patent seat post, the term "saddle candle" is often used today.
Patent seat posts
With modern patent seat posts , tube and block form a unit. As a result, a more robust connection from the saddle to the support is achieved than with the multi-part connection elements made of sheet metal that were customary in the past and did not reliably prevent the unintentional adjustment of the saddle inclination. Patent seat posts are available in a backward-cranked version ("offset seat posts"), whereby the center of the saddle rail clamp and thus the position of the saddle is behind the center axis of the seat tube, which leads to a greater distance between saddle and handlebars.
There are numerous different designs for attaching the saddle to the seat post. For many, the saddle is only fixed with a single ( Allen ) screw. There are particular differences in the type of angle adjustment of the saddle. Sometimes there are only rough rest steps; other seat posts allow a stepless adjustment. Ideally, the saddle is clamped independently of the angle adjustment so that the inclination of the saddle can be changed without accidentally moving it and vice versa. If there are two other, smaller Allen screws on the head of the seat post next to the larger clamping screw, the inclination of the saddle can usually be adjusted by unscrewing one of these screws and screwing in the other to the same extent.
At the beginning of the 1990s, oval or teardrop-shaped patent seat posts were introduced on the grounds of lower air resistance . The meaning is controversial as these seat posts are often heavier.
Suspension seat posts
Sprung seat posts can be used as an alternative to the rear suspension are used. Compared to a suspension frame, they have the disadvantage that the distance from the pedal to the saddle changes. In addition, the unsprung mass is greater, which leads to poorer responsiveness. With the usual, relatively short spring travel of 25 to 50 mm, this does not play a major role. If the spring force is set correctly, the saddle lowers by around a third of the spring travel when the driver sits up, so that the seat height only changes by 20 mm to 35 mm while driving. Any type of suspension reduces the stress peaks that act on the bicycle and thus extends the life of the material to a certain extent. On the other hand, suspension increases the number of moving parts on the bike that have to be serviced and replaced if worn or broken.
In addition to the gain in comfort, suspension forks and spring-loaded rear structures improve the grip of the wheels, thereby increasing safety and enabling higher speeds on uneven terrain. Due to the higher unsprung mass and the limited spring travel, a suspension seat post cannot generally do this. Rather, its purpose is to increase driving comfort, which enables relaxed, pain-free and persistent pedaling, especially on longer journeys. Even a simple spring-loaded seat post with short suspension travel can make driving on uneven surfaces noticeably more comfortable and enables driving while sitting even if driving while standing would otherwise be preferred due to hard bumps.
The saddle of a bicycle with a suspension seat post should be set a few centimeters higher to compensate for the compression of the post when the rider sits down. For inexperienced cyclists, this can temporarily lead to uncertainty when standing or climbing.
With spring-loaded telescopic seat posts, a tube with a smaller diameter plunges into the actual seat post during compression. In the case of low-quality seat posts, there were rarely problems with material breakage in the upper area. In the case of insufficient lubrication or poor material quality, telescopic seat posts have a poor response behavior to light impacts due to the high friction when the tubes slide into each other inevitably tilting.
Technically more complex seat posts not only guide the saddle down during compression, but also backwards via a parallelogram construction. This increases the distance between the saddle and the handlebars, while the seat height changes less significantly while driving. Since the impact comes from the rear when rolling over an obstacle with the rear wheel, the direction of the evasive movement of these seat posts corresponds more to that of the impact pulse.
The full suspension of a bicycle can, in the worst case, absorb up to 20 percent of the energy put on the pedal by the rider through friction and damping. This reduces the amount of energy that has to be applied to deform the other components of the wheel on uneven ground. Due to the more even and relaxed driving style, a suspension can lead to an overall improved use of energy.
An alternative to suspension seat posts is the use of wide tires (e.g. in sizes 2 "to 2.5", which corresponds to a width of 50 to 65 mm) with a relatively low air pressure of 1.8 to 2 , 5 bar can be driven. Despite the increased rolling resistance on level road surfaces, this is common on mountain bikes that are moved off-road, as low air pressure improves grip on soft and smooth surfaces and, on uneven, unpaved surfaces, possibly also improves energy efficiency. The tubeless assembly of bicycle tires , introduced at the beginning of the millennium, enables even lower air pressure.
Vario seat posts
Vario seat posts can be adjusted in height while driving. To do this, the driver actuates a lever under the saddle or a button on the handlebar. The weight on the saddle pushes it down, without any weight the saddle moves up (similar to adjusting the height of an office chair ). There are versions with infinitely variable adjustment and with two or more levels.
Special forms
Bike ball bikes have a special, horizontal seat post.
Adjustment of the seat post
The optimal saddle height is usually determined by the cyclist assuming a normal sitting posture and placing the heel of one leg on the low pedal without tilting the hip to one side. If you wear a shoe with a flat sole, your leg should now be able to stretch out completely. In everyday life, a seated position that is too low is often preferred, as this enables better control of the bike, especially when starting and getting off the bike. However, effortless, persistent and knee-friendly pedaling is not possible in this way.
Once the maximum length of the seat post has been reached, it should be replaced by a longer and correspondingly stronger seat post. For mountain bikes and BMX bikes with a sloping top tube, seat posts longer than 40 cm are common. With classic frames with a horizontal top tube, you can already think about buying a bike with a larger frame (longer seat tube) when the seat post is 20 centimeters out of the frame.
There are a multitude of opinions and measurement methods about the frame size and geometry that match your body type. The lowest common denominator for adapting a sporty bike to the rider seems to be to first find out the position of the handlebar grips by selecting a suitable frame, handlebar and handlebar stem, which is the most relaxed and durable when standing . It is then determined whether a suitable saddle position can be found within the scope of the respective frame. This procedure requires a cyclist with enough experience to be able to assess the ideal posture for the respective conditions. It is based on the assumption that - starting with the bottom bracket as a fixed point - the grip position can only be varied within a narrow range when riding in a standing position, in order to enable a balanced body and relaxed arm posture. The horizontal distance from the saddle to the bottom bracket, on the other hand, is of secondary importance and may have to be corrected by choosing a different frame geometry (for example, if there is an unfavorable weight distribution between the front and rear wheels).
Safety risk in the event of incorrect assembly
In most cases, the minimum length of the seat post that has to be pushed into the seat tube is indicated by a circular marking in the form of a series of short vertical lines on the post. This marking should not be visible when the seat post is installed in order to avoid fatigue of the material and a break above the seat clamp or overstressing of the frame in this area. If there is no marking on the seat post, at least 65 mm of the seat post should be trapped in the seat tube. If the clamp between the seat post and the saddle is not correctly installed (“tooth on tooth”) or is not tightened sufficiently, it can loosen and cause the saddle to tilt suddenly. This can lead to a fall, especially when driving hands-free.
Seat post problems
Steel frame with screw eyes
On inexpensive bikes, the seat post is secured with a steel screw, the flat head of which has a cam on the support side that is held in a groove in the eye. If the groove and cams wear out, the screw will turn as you tighten. If a new screw cannot hold itself in the groove either, it should be replaced with a combination of Allen screw and sleeve or with a simple machine screw with washer. Since an ordinary 6 mm machine screw may not be strong enough, the hole in the clamp may need to be drilled or reamed with a reamer in order to use an 8 mm machine screw. If the clamping sleeve is only pushed on and can be removed, it can also be completely exchanged for a new clamp.
Patent supports in teardrop shape
Aluminum or carbon supports that are greatly reduced in weight can break in the head without warning. In heavy drivers, train wheels or travel wheels a tendon may like the well-known of sailboats Rigging be mounted under the nose of the saddle. The other end of the tensioner grips the top tube of the frame so that the seat post is relieved.
Dimensions
Often the diameter of the support is stamped in the lower or upper part of the pipe; otherwise a caliper can be used to determine the diameter.
Reduction sleeves are available that allow seat posts to be used in seat tubes with a larger diameter. Higher-quality sleeves are usually intended for seat posts with the standard diameter of 25.4 or 27.2 mm, and the corresponding seat tube diameter is stamped on them. Since the sleeves are usually slotted, they can also be used for seat post / seat tube combinations with similar dimensions by being slightly bent or compressed.
| Diameter [mm] | Standard and racing frames (mainly made of steel, partly aluminum) |
|---|---|
| 20th | Children's and art bikes |
| 21.15 (13/16 ") | BMX bikes |
| 21.8 | Rare |
| 22.0 | Rare |
| 22.2 (7/8 ") | BMX and other US bikes |
| 23.4; 23.8 | rare (80s, e.g. at Peugeot) |
| 24.0; 24.2; 24.6 | 24.0 z. B. GDR bikes until 1989 (Diamant et al.) |
| 25.0; 25.2 | Steel frames in the 1960s & aluminum frames in the 1980s (e.g. Alan, Biria, Look, Panasonic, Raleigh, Vitus) |
| 25.4 (1 ") | Standard size up to the 1990s (e.g. classic Raleigh racing bike frames) |
| 25.6; 25.8 | Occasionally used (25.8 mm for aluminum frames from the 1990s and e.g. Diamant, Motobecane, Raleigh) |
| 26.0; 26.2; 26.4; 26.6 | Children's bikes and racing frames of simple quality (e.g. Motobecane, Nishiki & Peugeot in the 70 & 80s; Raleigh, Schwinn, Specialized & Trek in 80 & 90s; 26.6 mm e.g. at Bianchi, Giant, Nishiki & Patria) |
| 26.8 | Medium quality racing frames (also e.g. Bianchi, Klein, Koga Miyata, Marin, Raleigh, Rocky Mountain, Schwinn, Scott, Specialized) |
| 27.0 (1 1/16 ") | occasionally used (e.g. Marin, Motobecane, British steel frames in the 80s) |
| 27.2 | Standard size for (high-quality) road bikes (also children's bikes; such as Cannondale, Trek) |
| 27.4 | rarely (e.g. Klein, Raleigh) |
| Diameter [mm] | larger frame tubes (mainly mountain bikes with aluminum frames) |
|---|---|
| 28.0 | older French frames |
| 28.4; 28.6 (1 1 // 8 ") | rarely (28.6 mm e.g. with Giant, as well as with tandems , in order to be able to attach a common 1 1/8 "clamp stem for the handlebars of the person behind you to the front seat post) |
| 29.2; 29.4; 29.6 | occasionally used (e.g. 29.2 mm at Raleigh & Trek) |
| 29.8 | some manufacturers (from the 1990s; e.g. Corratec, German Centurion, Trek) |
| 30.0; 30.2; 30.4; 30.6; 30.8; 30.9 | less often (e.g. 30 mm for Marin; 30.2 & 30.8 mm for Giant
|
| 31.2; 31.4; 31.5 | rare (e.g. 31.2 mm for Peugeot; 31.4 mm for Marin) |
| 31.6 | Standard dimension (from the turn of the millennium; e.g. cube, small) |
| 31.8 | rarely (e.g. at Raleigh, Haibike) |
| 33.9 | for folding bikes (e.g. Tern , Dahon , Brompton ) |
| 34.9 | for high-quality sports bikes (from the turn of the millennium) and folding bikes (e.g. B'Twin, Riese and Müller ) |
literature
- Hans-Christian Smolik, Stefan Etzel: The large bicycle lexicon. BVA , Bielefeld 2002, ISBN 3-87073-127-3 .
Web links
- Glossary: Saddle joint by Christian Smolik
- Adjust the bike correctly
- Instructions for adjusting the saddle at Selle Anatomica
- Instructions for adjusting the saddle and adjusting the bike at Patria
- Bicycle Wiki
Individual evidence
- ^ Van der Plas, Rob: The bicycle - technology - maintenance - repair , Ravensburger Buchverlag Otto Maier GmbH 1989, ISBN 3-473-42564-8 , p. 41 u. 140
- ↑ a b c d e f Sheldon Brown, John Allan: Seatpost Size Database
- ^ A b Sheldon Brown, John Allan: Threading / interchangeability issues for older Raleigh Bicycles
- ↑ Technical information from Christian Smolik
- ↑ Technical information from Christian Smolik