Bicycle fork
The fork of the bicycle is designed as a holder for holding the front wheel and is therefore sometimes referred to as the front fork. Means of the control block is rotatably mounted in the head tube of the bicycle frame, forming with the horizontal an angle ( so-called steering head angle) of about 70 to 85 degrees. The fitted width of the front hub, depending on the type of bike 81 to 100 mm, in contrast, forks usually have a fork failure of 100 mm.
- 2.2.1 suspension 2.2.1.1 steel springs
- 2.2.1.2 Air suspension
- 2.2.1.3 elastomers
- 2.2.1.4 Other
- 2.2.2.1 Encapsulated damper
- 2.2.2.2 Open cartridges
- 2.2.2.3 Integrated damper
Rigid fork
Rigid forks are the classic bike forks and are not equipped with springs as opposed to suspension forks. They are made of steel, aluminum or carbon fiber tubes and its advantages over forks are lower mass, resistance to wear, low maintenance and usually also lower costs. Therefore, be on road bikes and BMX sports mainly mounted rigid forks.
Steel is the classic material for rigid forks and standard on all older bikes to early mountain bikes. In the 1990s, steel forks were more and more replaced by aluminum forks. The most rigid forks are slightly bent down forward so that they provide a certain suspension in conjunction with the elasticity of the material when driving over uneven road surfaces. Because aluminum tends under such dynamic bending loads to cracking, aluminum forks are engineered for greater rigidity than other forks. The latest development of the rigid forks are carbon forks, which are lighter than aluminum forks. However, they are mainly in the area of stem sensitive and tend to cost more than aluminum forks.
Fork
Unlike a rigid fork, a suspension fork to improve soil contact and comfort with springs and shock absorbers is equipped. Although forks are known since the beginnings of the modern low wheel, they found only by the spread of mountain bikes in the 90s the way into the mass market.
Forks usually have 200 mm of travel, all mountain ( enduro ) 140 to 180 mm and cross country around the 80 to 100 mm in the downhill. Increasingly, suspension forks are also used in everyday bikes.
Designs
Telescopic fork
The suspension consists of a standpipe and a slider that slide into each other during compression. The standpipe is in relation to the frame fixed tube, so always the top. The lower moving pipe on which the hub is mounted, the guide tube. The stanchion tubes are held together under the steerer tube by a fork bridge that carries the steerer tube in the middle.
The inner tube is usually made of chromed steel or, in modern and / or more expensive forks, made of coated aluminum. Exotic materials such as titanium or carbon have hardly been used. The outer tube is usually made of magnesium alloys, aluminum only in favorable models at very cheap forks even steel will be used.
RightSideUp
The most common design of the fork is the RightSideUp suspension fork, which means "right side up ". In this version, the thinner mounted in the fork bridge standpipes dive into the thicker dip tubes in which the hub is mounted. The dip tubes are connected to the wheel so that the torsional forces during steering does not have to be derived from the hub. Since the standpipes are stored in the lowers with simple and plain bearings, the dip tubes could rotate freely about the standpipes, if they were not related to the tire. In addition, the load on the two dip tubes can vary greatly when the bicycle is tilted or the front wheel gets into longitudinal grooves. Also the thereby occurring force difference between the dip tubes should be collected from the hub when the dip tubes would not be rigidly connected to each other via the tires.
Upside Down
In USD technique ( USD Upside Down ) the thinner dip tubes in which the hub is mounted in the thicker stanchions dunk, which are fixed in the fork bridge. This stability is increased because the thicker tubes are above, where the greatest leverage forces. The unsprung mass ( sliding tubes, hub, wheel) is smaller, which leads to a better sensitivity of the fork, especially in fast shocks. The USD technique is mainly downhill and extreme freeride use, as is paying only here the more elaborate technique. The suspension forks for cross-country area, the benefits are felt almost since the forks are optimized here on light weight and have little travel.
The connection of the dip tubes on the bike does not exist with Upside Down Forks, of course, since the sliding tubes so immersed here in the standpipes. To connect the sliding tubes, so you would have a very long strap from the hub construct over the wheel to the other side of the hub. That would weigh much and still stay strong twist. Therefore, the forces mentioned above are taken solely from the hub axis at Upside Down forks. To this end, we used hubs with thick axles, which are large areas bolted to the sliders.
It was upside down forks with a slit in the stand pipes through which the sliding tubes are available. So you can connect the sliding tubes like a RightSideUp fork with a bridge over the wheel, thereby reducing the load on the hub to the extent that one can use ordinary hubs. Through the slots in the fork tubes of course, considerable problems in sealing the fork, so that this type is very rare and largely extinct.
Double bridge
In contrast to the usual Einbrückenfedergabel end at a double bridge fork stanchions not under the steerer tube, but are continued upwards to below the stem, where they end in a second fork bridge. Thus, the steerer tube is hardly subject to bending and the entire structure much more stable, but of course even harder. Disadvantage: Due to the high stiffness of the fork, the frame can break the head tube, if it is not designed for dual bridge forks. If you want to install such a fork afterwards, you should always ensure that the frame is suitable for this type of fork.
Parallelogrammgabeln
A Parallelogrammgabel consists of a rigid fork, which is suspended for at least two struts to the steerer tube. The struts are rotatably mounted on both sides, so that the fork can move up and down. The braces form a parallelogram with their shots.
An advantage of Parallelogrammgabeln is the sensitive response and the ability to hold by appropriate orientation of the struts, the compression braking low. If the braces and their shots are sized so that they only approximate yield a parallelogram, also can be kept almost constant by their corresponding arrangement of the caster during compression.
The problem that many wear- sensitive joints are in the area of greatest leverage forces that result in a rather low stability.
Suspension in the fork steerer tube
This type of suspension fork is built mainly by the U.S. company Cannondale under the name " HeadShok ". Here, the suspension technology is not plugged into the stand and sliders, but centrally in the steerer tube. Such a fork is, in principle, an ordinary rigid fork, the steerer tube is however stored with elaborate bearings resiliently in a second steerer tube. This makes the whole, actually rigid fork moves up and down in handy frame. The steering force is transmitted in these types of forks either by a polygonal cross-section of the steerer tubes or via a hinged joint that connects the two run into each other steerer tubes.
This construction offers a number of advantages. The largest is the massive stiffness compared to normal telescopic fork, as two parts slide in only one place ( in the head tube ) into each other. Thus, these forks are almost as rigid as rigid forks. In addition, any type of brake easily attach to the fork, which is not necessarily the case with the other fork structures.
One disadvantage is to, above all, the need for a steerer tube that does not conform to standard dimensions. That might also be the reason why this construction that has already been patented in the 50s, the 90s found only in a certain distribution.
Suspension and dampers
The tasks are divided into a suspension fork springs and damping. The springs absorb once the impact energy. This energy is stored but only in the springs that would spring back without damping during rebounding on the original position and start would oscillate.
Therefore, there is the attenuation (usually by oil ), which already assists during compression, but mainly controls the rebound movement and braking. This is evident with cheap suspension forks without attenuation, especially at high speeds which tend to wildly jump and zurückzuschnalzen.
As with all physical processes also only an energy conversion takes place, that is, the fork, the shock power does not just disappear into nothingness. Specifically, kinetic converted into thermal energy. In the beginning is the kinetic energy of jounce. The damping oil is forced through narrow channels, heats up, and so is the energy in the form of heat again.
Suspension
Steel springs
The classical and simplest solution is the suspension with coil springs made of steel. They are robust and provide a linear spring curve. For weight reasons, but also a suspension with air is very common. High quality damper, which are provided with steel springs, built mainly in the freeride or downhill area. Alternatively, springs can be installed from titanium. However, this has a significant weight reduction result is even more expensive.
Air suspension
For forks with air suspension, one encounters the problem that the compressing air a very progressive curve with a high initial value is often caused by fitting a second air chamber, which counteracts the pressure of actually resilient air and thus reduces the amount of initial force. Some forks steel springs are installed as a counter, but this is common only in the lower price segment. The characteristic of the suspension can be adjusted then by a suitable choice of the volume ratio of the two air chambers. In an air fork you can very easily adjust the firmness of the suspension by the air pressure. At the early days of air suspension, there were still problems with the air in the damper to be heated by the friction. The air expands when heated, thereby affecting the damping. This was then harder and ultimately uncontrollable. Thanks to modern technology, these problems could be overcome, however, as far as possible.
Elastomers
Suspension by means of elastomers is only to be found because of strong temperature dependence and lack of durability in the lower price segment, although these have a quite good effect, but it occurred permanent deformation after some time.
Other
Other possible suspension, for example by means of resilient carbon fiber elements ( for example Remec ), never got over the experimental stage addition, even if there were attempts by some manufacturers, so something to sell. Partial try Carbon & Titanium frame manufacturer (for example, Cannondale, Moots ) to consider the flex end characteristics of the material in their designs so that it covers the material as a leaf spring shape on the rear chain stays and thereby obtain a resilient effect, which only at the seat stays must be performed. Titanium springs Chance at spring dampers used for weight reasons instead of steel springs.
Damping
An oil damper is almost always used for damping. Few air damped forks achieve by letting the compressed air to flow through very small holes, a kind of damping. Friction losses are extinct due to poor function and high wear. At very inexpensive forks usually no damping is present.
Bicycle forks there is no predominant Shock as opposed to automotive technology. Rather constantly new ways be devised to attenuate the fork. Although all dampers oil through (often variable ) holes to provide the damping effect. How this is achieved in the individual, but is different from manufacturer to manufacturer, and often also by the model year model year. Roughly speaking, one can classify three types of dampers:
Encapsulated damper
Fully enclosed ( encapsulated ) dampers which are installed as a complete, finished component in the fork. This is the dampers used in the automotive sector in the next. These dampers are also referred to as a closed damper cartridges or cartridge- damper. These dampers have the problem that they can not absorb a lot of energy because they have a very low volume of oil in the rule. Also, there is usually no expansion tank for the expanding when heated oil. For these reasons, there were in the past major reliability problems with such dampers.
Open cartridge
Damper cartridges are dampers that do contain the necessary pistons and bores, but have to rely on to get their oil from a surrounding oil bath. These dampers are also referred to as "open cartridge" damper or "open bath" damper. Their advantage is the opposite a closed damper simpler structure and the usually much larger oil volume. Due to the larger amount of oil such dampers can absorb more energy that is emitted in the form of heat to the oil. Moreover, the surrounding oil is often used to lubricate the bushings of the standpipes.
Integrated damper
Damper constructions are built into the cradle. In this case, the damper is not provided as an independent part, but the cushioning effect is achieved by special design of some of the design of the fork in any case necessary parts. This allows you to save weight, which is why this construction is applied in almost all weight-optimized forks. However, such a structure raises a number of, sometimes technically difficult problems to be solved, in particular with regard to adjustability of the damping and reliability. Therefore, this type of damping with inexpensive forks is rare to find.