Das 1x1 der Felgenbremsen
Dieser Artikel beschreibt die verschiedenen Arten von Felgenbremsen, deckt alle gemeinsamen Themen ab und verweist wo nötig auf spezielle Artikel, die zusätzliche Informationen liefern.
Warum Felgenbremsen?
Fahrradbremsen zerfallen in zwei generelle Kategorien: Nabenbremsen und Felgenbremsen, bei denen die Felge die zweifache Aufgabe als ungwöhnlich große Bremsscheibe erfüllt.
Die Felgenbremse funktioniert bei jeder beliebigen Laufradgröße gleich gut, weil die Geschwindigekit der Felge zur Bremse immer ungefähr gleich bleibt. Da die Felgenbremse nahezu am äußeren Rand des Laufrads wirkt, ist die Klemmkraft für eine bestimmte Bremswirkung wesentlich geringer als bei einer Nabenbremse. Durch die deutlich geringere Kraft werden Rahmen und Gabel weniger beansprucht als bei einer Nabenbremse. Felgenbremsen sind relativ sicher zur Kontrolle über die Geschwindigkeit bei langen Bergabpassagen für ein (Ein-Personen-)Fahrrad, weil die Felgen eine große Fläche für Hitzeableitung bieten.
Felgenbremsen haben allerdings auch Schwächen. Auf einem Tandem können sie die Felgen überhitzen und so zu platten Reifen führen. Ein schlecht eingestellter Bremsschuh kann den Reifen zerstören oder unter der Felge durchtauchen und mit einer Speiche das Laufrad komplett blockieren. Manche Felgenbremsarten haben Gelenke über dem Reifen und funktionieren durch den notwendigen sehr langen Hebelweg, der für dicke Reifen benötigt wird, schlechter. Nasse Felgen reduzieren die Effizienz der Bremse drastisch bei billigen Stahlfelgen und moderat bei Aluminiumfelgen.
Alles in allem sind Felgenbremsen jedoch einfach und praktisch. Man sollte ihnen den Vorzug geben, wenn Ökonomie, sportliche Leistung und Leichtbau im Vordergund stehen.
- Siehe auch
Felgenbremsentypisierung
Es gibt zwei grundlegende Arten von Felgenbremsen
Diese haben einen in sich geschlossenen Mechanismus, der mit einer einzelnen Schraube am Rahmen (oder der Gabel) oberhalb des Reifens befestigt wird. Die Bremsarme verlaufen nach unten und müssen lang genug sein, um um den Reifen herumzureichen. Das Gelnk kann dabei in der Mitte um die Befestigungsschraube sein, oder auch weiter Gelenke aufweisen.
Cantilever Bremsen haben zwei getrennte Arme, die jeder für sich auf jeder Seite des Rahmen oder der Gabel montiert werden. Nicht jede Cantilever Bremse sieht so aus wie auf dem Bild, sie haben jedoch alle zwei getrennte Arme. Sie können ausschließlich an Fahrrädern montiert werden, die dafür vorbereitet sind, da man spezielle Bremssockel benötigen.
- Siehe auch
Über Züge
Die meisten Probleme bei Bremsen resultieren aus exzessiver Reibung oder schlechter Montage der Züge. Sie resultieren weniger aus schlechtem Aufbau oder geringer Qualität der Bremse.
- Siehe auch
- Züge
- Bremsbeläge ausrichten auf dieser Seite
Über Felgen
Damit eine Felgenbremse vernünftig arbeitet, muss die Felge sauber sein und eine einheitliche Breite aufweisen. Das Laufrad muss zentriert sein. Eine verzogene oder eingedellte Felge sorgt dafür, dass die Bremse zupackt. Eine Felge, die von der einen Seite zur anderen wankt, schleift abwechselnd an beiden Bremsschuhen und wird Dich langsamer machen, ob Du willst oder nicht. Eine Felgenbremse kann schleifen, wenn sie nicht richtig eingestellt ist.
- Felgenschnitte
Felge mit parallelen Flanken (abgedrehte Bremsflanken)
Felge mit angewinkelten Flanken
Die meisten modernen Felgen (für Felgenbremsen) haben abgedrehte Felgenflanken. Bis in die 1970er Jahre hinein hatten Felgen abgewinkelte Flanken. Die meisten Bremsen waren nicht dafür vorgesehen, die Bremsbeläge entsprechnd auszurichten. Zudem agiert die Flanke wie ein Keil, die die Felge effektiv breiter macht je mehr man sich der Nabe nähert. Eine Felgenbremse würde hier wirken, sobald sich die geringste Unebenheit durch schludriges Zentrieren oder durch Einwrkungen einer Bordsteinkante oder eines Schlaglochs ergibt. Felgen mit angewinkelten Flanken begünstigen Rattern der Bremsen. Es gibt weiterhin Felgen mit angewinkelten Flanken. Diese sind für den Betrieb an Laufrädern mit Nabenbremsen optimal und solten möglichst nicht mit Felgenbremsen benutzt werden.
Besonders im Winter oder im Gelände leiden die felgenflanken unter Abrieb. Das macht sich bei Aluminiumfelgen durch ein dunkelgraues Pulver bemerkbar, das sich schlecht von Händen und Kleidung entfernen lässt. Wenn hierduch die Felgenflanken zu dünn werden, können sie reißen. Dass Aluminiumfelgen dieses Problem haben, ist schlimm genug. Felgen mit Flanken aus Carbonfasern sind leicht, verschleißen jedoch schneller. Sie benötigen spezielle Bremsbeläge und sind sehr teuer. Die meisten modernen Felgen haben eine kleine Vertiefung in der Flanke, die eine sichere Verschleißanzeige darstellen. Wenn die Vertiefung verschwindet, sollte die Felge ersetzt werden.
Typisierung der Bremsschuhe
Der übliche Aufbau eines Bremsschuhs besteht aus Bremsbelag und der Bremsbelagaufnahme (häufig kann man den Bremsbelag von der Aufnahme trennen, um ihn zu wechseln).
Ältere Bremsschuhe waren an einem Ende offen, so dass man den neuen Bremsbelag einfach einschieben konnte. Wenn man unachtsamerweise den Bremsschuh falscherum montierte, konnte der Belag beim Bremsen herausgeschoben werden. Moderne Bremsschuhe sind diesebzüglich idiotensicher - sie sind entwdere an beiden Enden geschlossen oder der Belag wird mit einem Sicherungsstift in Position gehalten.
Man kann auch bei den geschlossenen Systemen mit Hilfe eines flachen Schraubendrehers den Bremsbelag entfernen. Dazu muss man eine Kante an der Schmalseite der Aufnahme mit dem Schraubendreher herunterdrücken und kann dann den Belag herausschieben. Wenn der neue Bremsbelag in Position ist, biegt man die Kante wieder hoch. Dabei kann es sinnvoll sein, den Bremsschuh in einen Schraubstock einzuspannen.
Bessere moderne Bremsschuhe haben eine Metallplatte mit dem Belag verpresst.
- Bremsschuhe mit unterschiedlichen Befestigungsbolzen
Befestigungsbolzen ohne Gewinde
Befestigungsbolzen mit Gewinde und flachen Unterlegscheiben
Befestigungsbolzen mit Gewinde und sphärischen Unterlegscheiben
Allgemein üblich sind Bremsschuhe, die euf einer Seite des Befestigungsbolzens länger sind. Diese Bremsschuhe sind vergleichswiese flach, so dass in den relativ engen Platz zwischen Felge und Gabelscheide hindurch passen, obwohl sie im Vergleich zu älteren Bresschuhmodellen lang sind.
Bremskräfte tendieren dazu, die Bremsschuhe leicht zu bewegen, so dass die nach hinten gerichtete Seite stärker anpresst als die vordere Seite. Um den Druck in etwa gleich über den Bremsschuh zu verteilen, sollte die längere Seite bei der Montage nach hinten weisen. Daraus resultiert dann ein gleichmeäßiger Verschleiß und die Tendez zum Qietschen nimmt ab.
Es gibt grundsätzlich zwei Arten, einen Bremsschuh am Bremsarm zu befestigen. Einmal mit einem Befetsigungsbolzen mit Gewinde und einmal ohne Gewinde, der durch einen anderen Bolzen mit Loch geschoben wird.
Gewindelose Befestigungsbolzen werden überwiegend bei klassichen Cantilever Bremsen und Mittelzugbremsen eingesetzt. Bei moderneren Bremsen können sie in jede notwendige Richtung justiert werden. Bei älteren Bremsen - wie den klassischen Mafacs - gab es keine Möglichkeit, den Scherwinkel einzustellen. Inzwischen (seit den 1970er Jahren) bieten aber die meisten Cantilvere Bremsen die Möglichkeit, jede Richtung einzustellen.
Befestigungsbolzen mit Gewinde und flachen Unterlegscheiben haben nur minimale Einstellmöglichkeiten. Aus diesem Grund sind sie nicht empfehlenswert.
Wenn die Unterlegscheiben jedoch spährisch sind, können alle Winkel eingestellt werden. Eine zentrale Rolle spielen hierbei die konvexen Unterlegscheiben, die jeweils nach Außen und Innen weisen und zwei konkave Unterlegscheiben, die passend zu den konvexen aufgeschoben werden.
Normalerweise haben die konkaven Unterlegscheiben unterschiedliche Stärken, so dass man entscheiden kann, ob man die dickere oder dünnere Unterlegscheibe Innen montiert.
Bremsbeläge ausrichten
Bremsschuhe können in fünf Dimension eingestellt werden
- Höhe
- Rollwinkel
- Neigungswinkel
- Scherwinkel
- Abstand
Höhe
This is the most critical adjustment. The shoe should contact the rim fully, but not overlap it. If the shoe is set too high, it will rub on the tire, destroying it very quickly. If the shoe is set too low, it can "dive" under the rim and get caught in the spokes, causing dangerous wheel lockup.
Most rim brakes have a slot in each brake arm. Height is adjusted by sliding the brake shoe post or eyebolt up or down the a slot. Different brakes have different ranges of adjustment. Sometimes, getting the height correct may require replacing a brake.
On mountain bikes with narrow rims and big bulgy tires, it may be quite difficult to get a good height adjustment with a cantilever brake that has frame or fork-mounted pivots below the rim. The shoe may clear the tire when the brake is engaged, but it may rub on the sidewall of the tire in its rest position.
With these cantilever brakes, as the brake shoe material wears down, the shoe hits lower and lower on the rim, increasing the risk of "diving" into the spokes. With other rim brakes, the shoe migrates up toward the tire. Periodic checking is in order.
Rollwinkel
The roll angle should be set so that the shoe hits the rim squarely, both the top and bottom of the shoe should meet the rim. If this is not set perfectly, normal pad wear will eventually even it out, but braking will be less effective until the shoe has worn in.
When you readjust the roll angle, you may also have to readjust the height.
Neigungswinkel
The pitch angle should be set so that the shoe follows the curvature of the rim as closely as possible. Brakes arms can flex slightly in hard use, changing the pitch angle. You may need to adjust the brake shoes to compensate, so the brake shoes don't contact the tire. Check by leaning over the bicycle and, pressing your weight down on the saddle while rolling it forward and applying each brake.
Scherwinkel ("einwärts")
The shoe should be set so that the front edge of the shoe contacts the rim slightly before the rear edge. This is commonly called "toe-in." If this is not set perfectly, normal pad wear will eventually even it out, but braking will be less effective, and the brakes may squeal until the shoe has worn in.
The traditional way to adjust yaw angle was to bend the brake arms. This can lead to failure of aluminum brake arms -- see comments by Jobst Brandt. Use brake shoes with spherical washers, or replace a smooth-stud brake that does not allow yaw-angle adjustment.
Abstand
Extension is the adjustment of the distance from the pad braking surface to the brake arm. Setting the shoes farther away (inward) from a cantilever arm generally increases the mechanical advantage, by increasing the cantilever angle.
The small cantilever angle of newer, narrow-profile cantilever brakes causes the anchor arm to be nearly vertical, especially on mountain bikes that have wide-set pivot bosses and narrow rims. Traditional good practice had been to slide the brake shoe holders all the way into the eyebolts, so that the back of the shoe butts up against the cantilever arm, reducing the likelihood of slippage and brake squeal. .
With the newer low-profile cantilevers, the shoe needs to be extended inward from the arm, increasing the effective cantilever angle. The unsupported length of shaft connecting the brake shoe to the arm may cause an increased tendency to squeal, but that is one of the inherent trade-offs of low-profile brakes. Increasing the extension by only a few millimeters can often dramatically improve the performance of these brakes.
With other types of rim brakes, it is usually best to keep the shoes as close to the arms as they will go, for the sake of rigidity.
Sometimes it is difficult to get all 5 adjustments set at once, and to get the brake shoe tight enough without twisting it out of position. It helps if you remove the nut and lubricate the threads, being careful not to get any lubricant on the rim or the brake shoe.
Probably the best way to adjust the shoes is to use the Shimano technique:
- Set the adjusting barrel 2-3 mm from fully closed.
- If using a cantilever brake or centerpull brake, set the link wire so that the guide line on its button lines up with the cable. If you're using a traditional yoke instead of a link wire, set the respective lengths of the main cable and transverse cable appropriately.
- With the brake in this relaxed position, adjust the brake shoes so they're touching the rims.
- Close down the adjusting barrel. This should allow the brake shoes to withdraw just enough to clear the rim.
Geräusche
Rim brakes that are working properly are generally quiet. Noises indicate problems and can also help you diagnose them.
Klappern
A chattering sound while braking may result from sticky brake-shoe deposits on the rim, or from a loose or flimsy brake. Chattering is common with cheap brakes that have thin, stamped-steel brake arms, and may require replacement of the brake. A rim with angled sidewalls promotes chattering, as the flexibility of the brake assembly allows it to ride upward toward wider part of the rim, closer to the tire -- and grab; then downward toward the hub, and loosen.
Rattern
You may hear a rattle and feel it through the handlebar when you apply the front brake lightly. The rattle stops when the brake is applied harder. The problem isn't actually in the brake at all: it is a loose headset. When you are not using the brake, your weight pushes the front fork forward. Braking pushes it backward and at some point, the forces balance and road irregularities rattle it back and forth.
A rattle that occurs when the brake is not applied and goes away when it is applied, indicates that something is loose. -- most likely, a brake pivot, or the bolt that attaches a caliper brake to the frame. Find the problem and fix it! A loose front brake that can jam in the spokes is very dangerous. A loose brake shoe can tilt and wear through the tire, or jam the wheel.
Klacken
If you bear down with your belly on the saddle and try to roll the bicycle backwards and forwards while holding a brake lever, some of the rattles described in the previous section become clunks. A clunk indicates that something is loose. Fix it!
A clunk that occurs once per wheel revolution while braking indicates that the rim has an irregular braking surface. See the longer discussion of this topic in Sheldon's article on creaks and clunks.
Schaben
Some brake shoes intended for off-road use are made of unusually hard material. It is normal for these brake shoes to make a light scraping noise in use.
Other than this, a scraping noise when the brake is applied is probably from a worn brake shoe whose metal backing plate contacts the rim. Replace the brake shoe before it wears a groove in the rim sidewall.
Musikalischer Tone, der sich mit der Geschwindigkeit verändert
A musical tone may appear when you apply the brake. The musical pitch falls as the brake slows you down. Some older (pre-1980) rims had serrated sidewalls, and with these rims, this noise is normal, if unwelcome: brakes work better on smooth rims. More often, this noise results from a brake shoe that is contacting a tire. The vibration results from the pattern of the tire fabric. The brake shoe may be misadjusted, or the wheel may be misaligned -- see Sheldon's additional comments.
Some tires have smooth rubber on their sidewalls, and then this problem doesn't make a noise. Also check the brake shoes visually. Fix this problem before the brake shoe eats a hole in the tire!
Quietschen
Squealing of brakes is a common problem, and there's no one simple solution to it.
It's caused by the friction of the brakes against the rim flexing the shoes or brake arms, which then slip back, grab, slip back, grab, etc. at high rate -- like a violin bow on a violin string. All brakes do this, but with luck the pitch (frequency) is too high for human hearing.
Occasional squeaks are annoying, but they are generally not a safety issue. On the other hand, a loud and persistent squeal makes it hard to modulate the brake. It is usually caused by a new brake shoe that has not worn in, or by grease or oil on the rim.
You might think that an oily rim would make the brake slip. Instead, it softens the brake-shoe rubber, which leaves sticky deposits on the rim. The brake shoe catches on these, squeals and grabs.
Here are some things to try if your brakes squeal (and also see Jobst Brandt's advice):
- Avoid holding the rim with greasy hands! Hold the wheel by the spokes instead.
- "Toe in" the brake shoes, so that the front edge of the shoe hits the rim slightly before the rear edge. Not all brakes permit this type of adjustment, but most do. Don't bend aluminum brake arms: this can initiate cracking and lead to failure. Instead, replace the brake if necessary.
- Clean the rims with a good, oil-free solvent (citrus, alcohol, something like that.) In obstinate cases, wash.with dishwashing detergent and a nylon-bristle brush to clean brake-shoe deposits and remaining solvent off the rim; then rinse with water. Sanding the surface of a new brake shoe lightly will remove any slippery chemical deposits. Jobst Brandt recommends using a dusting of household cleanser on a wet rim, then riding and applying the brake to clean the brake shoes and the rim.
- If the pivots of your brakes are adjustable, make sure that you've eliminated as much play as possible without causing them to bind.
- Better brake shoes may help. I particularly recommend Kool Stop salmon-colored brake shoes.
- A "brake booster" may help. This is a horseshoe-shaped arch that connects the two cantilever bolts or centerpull pivots together, making the whole system more rigid.
Zentrieren
When the brake is released, the brake shoes retract away from the rim. Ideally, the shoes on both sides should back off by the same amount. If they don't, the brake is not properly centered. In extreme cases, one of the shoes may not retract, and may rub on the rim even when the brake is not being applied.
If a brake appears off-center, check first that the wheel is installed straight in the frame/fork. If the wheel is crooked, and you maladjust the brake to compensate, you are creating two problems where there was only one before.
If the brake is, in fact, off-center, it is often the result of too much friction on one of the pivots. Unhook or loosen the cable (the transverse cable, on a cantilever or centerpull brake) and try moving each brake arm individually by hand. They should move smoothly and freely, and always come to rest near the same position. If you suspect friction, unscrew the bolt that holds arm to the boss or pivot, and remove the arm. The surface of the pivot should be smooth, free from rust, and coated with grease. If it is rusty, that is usually a sign that the bicycle was sloppily assembled by the dealer who sold it. Use emery cloth or sandpaper to remove the rust, and wipe off the dust and sand. Coat the boss or pivot with grease, and re-install the brake arm.
Rückholfedern einstellen
If your wheels are centered, and your brakes are not, and, if the pivots are properly lubricated and free-moving, the brake shoes should be centered. If they are not, you probably need to adjust the spring tension on one or both sides Different types of brakes feature different systems for adjusting the springs.
- Most caliper brakes can be centered by rotating the entire brake assembly around the bolt that attaches it to the frame or fork. Loosen the nut that secures it, and hold the bolt steady, with a wrench if possible, so that it does not rotate as you retighten the nut.
On some older and cheaper caliper brakes, including those on many English 3-speed bicycles, the return spring is rigidly attached to the spring block, which fits between the brake arms and the frame or fork. The spring block has a concave surface to mate with the convex surface of the frame or fork. It does not rotate with the brake arms. These brakes can be centered only by bending the spring or repositioning the brake shoes.
- Spring attachment. Most cantilever bosses on newer bicycles have a series of 3 small holes next to the boss itself. These holes are meant to receive and anchor the end of the return spring. Depending on which of the holes you chose to put the spring into, you have a coarse adjustment of the spring tension. The top hole provides the highest tension, the bottom hole the lowest. For most installations, the middle hole is best. (Some bosses only have one hole.) Both sides should use the same position.
Shimano cantilever
- Many Shimano style cantilevers and linear-pull brakes have a small screw on one of the cantilevers for fine balancing. This is usually on the left side of the front brake, the right side of the rear. In the early '90's, this adjustment required a 2mm Allen wrench, but newer models use a Phillips screwdriver.
- Dia Compe style cantilevers often use a totally different approach. The Dia Compe system doesn't use the spring hole in the cantilever boss, but has a separate spring block as part of the cantilever assembly. This spring block is the first part to go onto the boss, and it has a hole for the end of the spring. When the bolt holding the cantilever to the boss is loose, the spring block can turn freely, but when this bolt is tightened, it locks the spring block in place. The spring block has flats for a cone wrench (usually 13 mm) to let you rotate it to provide the desired tension.
Some Dia Compe-style brakes have these adjustable spring blocks on both sides, others have one only on one side, with the other side using the normal spring holes in the boss.
Note: Brakes which use the adjustable spring block do not use the cantilever boss as a bearing surface; instead, they have a hollow cylindrical bushing (sleeve) which fits over the boss. The outside of this bushing/inside of the cantilever must be greased, as you would normally grease the boss.
- Non-adjustable springs are found in older or cheaper brakes. If these need adjustment, you must physically deform them. You can sometimes increase the tension of the spring by unhooking the transverse cable (or single cable of a sidepull brake) and forcing the brake arm out much farther than it would normally go. If that doesn't work, you may need to bend the spring after unhooking it from the brake, or slide a brake shoe stud in or out of the eyebolt, or reposition washers on a threaded stud.
Hebelkräfte und biegen
Mechanical advantage is a key concept, which you must understand before you will be able to choose and service brakes. Mechanical advantage is commonly referred to as "power", when discussing brakes, and it is common for people to confuse this with quality. A brake may be designed for any amount of mechanical advantage, but there is a fairly narrow range that is useable.
A few models of brake levers have adjustable mechanical advantage. Mechanical advantage may also be adjusted by changing the brake shoe extension or the length of the transverse cable if a brake uses one, or by replacing the brake, the lever or both. Pulley devices such as the Travel Agent also are available to adjust mechanical advantage.
Zu hohe Hebelkräfte
People with brake problems often think that they need more "power," when they actually need less! In particular, when modern low-profile cantilever brakes are used with drop-bar type brake levers, the combination produces excessive mechanical advantage. This problem also arises when using direct-pull cantilevers (such as Shimano's "V-Brakes") with levers made for other brakes. If there is too much mechanical advantage, the lever will be all-too-easy to pull, but it will run out of travel and bump up against the handlebar before the brake is fully applied. Once the lever hits the handlebar, it doesn't matter how much harder you squeeze! If you try to correct this by tightening up the cable, you will wind up with the brake shoes too close to the rim when at rest, which will cause them to rub, especially if the wheel isn't perfectly true.
Zu geringe Hebelkräfte
If your brakes too little mechanical advantage, when you squeeze your brake levers, you may feel a nice firm response. In fact, if you just squeeze the brakes of a bike that is not moving, your first impression may be that the brakes are in great shape, because they feel so solid and firm...the problem is, that they don't stop the bike, unless you squeeze very hard on the levers! A brake system with too little mechanical advantage will push the shoes against the rim quickly, but won't push them hard enough.
In some cases, what appears to be inadequate mechanical advantage turns out to be that the brake shoes are not "grippy" enough; they may be dirty, or dried out, or of low quality. Better-quality shoes can make a real difference. I particularly recommend Kool-Stop Salmon brake shoes, which have good grip and wear slowly.
Variable Hebelkräfte
Mechanical advantage can vary as the brake is squeezed.
Ideally, it should start out low, so that the brake shoes can be set for generous rim clearance. The low initial mechanical advantage will allow the shoes to move in toward the rim fast, in response to a small amount of hand-lever movement.
As the shoes get close to the rim, the mechanical advantage should increase, so that a small amount of hand force will result in a strong force pressing the shoes against the rim.
Some high-end brake levers, most notably the upper-end Shimano models with the "servo-wave" feature, are designed to do exactly this.
Unfortunately, conventional center-pull brakes produce exactly the opposite variation! As the lever is pulled, the yoke angle gets sharper and sharper, while, in the case of low-profile cantilever brakes, the pivot-cable distance decreases. Both of these conditions reduce the mechanical advantage as the brake is applied.
Since the travel increases as the brake shoes wear down, braking performance degrades as the shoes wear, not because the shoes have any less grip, but because the mechanical advantage has decreased.
Biegen
Preferably, every part of a rim-brake system is rigid except the brake shoes. Their compressibility allows them to conform to the shape of the rim and to take up the motion of the brake levers. If, on the other hand, the brake arms are flimsy and flexy, as on cheap long-reach sidepull caliper brakes, there is no way the brakes can develop enough "power". Most of the motion of the brake levers is wasted in flexing the arms. If the mechanical advantage is high, the brake lever will go to the handlebar before the brake shoes grip the rim very hard. If the mechanical advantage is low, the feel at the levers will be harder, but the brake will never develop enough grip.
Siehe auch
Quelle
Dieser Artikel basiert auf dem Artikel Bicycle Rim Brakes von der Website Sheldon Browns. Originalautor des Artikels ist Sheldon Brown.