Einstellen der Schaltung

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Dieser Artikel befindet sich in Übersetzung. Bitte nicht korrigierend eingreifen, bis dieser Hinweistext wieder entfernt wurde. --Bikegeissel 13:41, 29. Mai 2012 (UTC)

Die meisten modernen Fahrräder sind mit einer Kettenschaltung ausgestattet. Der Schaltvorgang wird dadurch ausgeführt, dass die Kette von einem Ritzel zuim nächsten umgelenkt wird. Schaltwerke und Umwerfer sehen kompliziert aus, sind aber tatsächlich sehr einfache Gerätschaften, die rohe Gewalt ausüben. Der (vordere) Umwerfer besteht aus einem einfachen Käfig, der aus einem Blech gebogen ist und von links nach rechts bzw. rechts nach links bewegt werden kann. Während dieser Bewegung nimmt er die Kette seitwärts mit und führt sie auf das nächstgelegene Kettenblatt in Bewegungsrichtung. Das (hintere) Schaltwerk sieht komplizierter aus, hat jedoch als einzige Verkomplizierung eine Arm mit unter Federspannung gesetzten Kettenführungsrollen, die dafür Sorge tragen, dass die Kette gespannt bleibt, wenn man auf kleinere Ritzel schaltet.

Schaltwerk und Umwerfer führen jeweils die Kette seitwärts, so dass die Kette nicht mehr gerade auf dem Ritzel bzw. Kettenblatt läuft, sondern in einem Winkel. Wenn dieser Winkel spitzer wird, können die Zähne des Ritzels (bzw. Kettenblatts) nicht mehr in die Zwischenräume der Kette greifen und sie fällt auf das nächstgelegene kleinere Ritzel bzw. Kettenblatt. Wenn die Kette auf das nächstgrößere Kettenblatt bzw. Ritzel geschaltet werden soll, funktioniert das etwas anders. Die Kette wird gegen die Seite des nächstgelegenen größeren Kettenblatts (bzw. Ritzels) gedrückt. Irgendwann bleibt sie an einem Zahn des größeren Kettenblatts (bzw. Ritzels) hängen und wird nach oben mitgerissen. Moderne Kettenblätter (bzw. Ritzel) haben Schalthilfen in Form von speziell geformten Zähnen und seitlichen Rampen, die dabei helfen, diesen Vorgang geschmeidiger ablaufen zu lassen. Das ist der Hauptgrund dafür, dass moderne Kettenschaltungen besser funktionieren als alte Systeme. Das hat sehr wenig mit der Qualität der Kettenschaltung zu tun.

Einstellen des Schaltwerks (hinten)

Bevor Du versuchst, ein Schaltwerk einzustellen, solltest Du sicher gehen, dass es nicht verbogen ist!

Bevor Du versuchst, ein Schaltwerk einzustellen, solltest Du wirklich sicher gehen, dass es nicht verbogen ist. Das Schaltwerk ist eines der zerbreclichsten und zugleich exponierten Teile am Fahrrad, das auch regelmäßig Stöße abbekommen kann.

Wenn ein Schaltwerk einen Schlag abbekommt, wird es nach Innen in Richtung der Speichen gebogen. Manchmal wird es tatsächlich zwischen die Speichen des sich drehenden Hinterrads gebogen. Das sind schlechte Nachrichten, falls das passiert. Wenn Du Glück hast, zerbricht das Schaltwerk in zwei Teile. Solltest Du weniger Glück haben, werden ein paar Speichen zerstört und möglicherweise das ganze Hinterrad unbrauchbar gemacht. Bei ganz besonders großen Pechvögeln wird das Schaltwerk von den Speichen mit solcher Gewalt nach hinten mitgerissen, dass das Ausfallende nach hinten verbogen oder gar mit dem Schaltauge abgerissen wird. Manchmal kann dadurch der ganze Rahmen abgeschrieben werden.

Bei einem starken Schlag ist es meistens nicht das Schaltwerk, das sich verbiegt, sondern das Schaltauge. Das liegt daran, dass ein Schlag meistens an seiner stärksten Stelle - dem Parallelogramm auftrifft. Beachte: Bei vielen älteren oder billigen Fahrrädern ist das Schaltauge nicht Teil des Rahmens, sondern werden als Bauteil des Schaltwerks mit ausgeliefert. Dieser Schaltwerk Adapter wird im wesentlichen von der Achsmutter oder dem Schnellspanner der Hinterachse geklemmt. Viele neuere Fahrräder besitzen ein austauschbares Schaltauge, das man wechseln kann, wenn es sich verbiegt.

Du kannst die Ausrichtung des Schaltwerks grob mit dem Auge kontrollieren, indem Du das Schaltwerk von hinten betrachtest. Die beiden Kettenführungsrollen sollten exakt untereinander angeordnet sein, so dass die Kette in einer exakt geraden Linie von der Spannrolle zur Leitrolle verläuft. Gleichzeitig solltest Du die Ausrichtung dieser Rollen zum darüber liegenden Ritzel betrachten.

Gut meinende Menschen schnappen sich oft das Schaltwerk und versuchen es manuell nach außen in die richtige Stellung zu biegen. Unglücklicherweise packen sie dabei das Schaltwerk am Käfig - seiner schwächsten Stelle - an. Dabei verbiegen sie dann nicht nur das verbogenen Schaltauge sondern gleichzeitig den Käfig. Merke: Gut gemeint ist in dem meisten Fällen nicht gut gemacht.

Wenn das Schaltauge verbogen ist, muss in den allermeisten Fällen das Schaltwerk demontiert werden, um es zu richten. Gute Fahrradwerkstätten haben ein spezielles Werkzeug (eine Art langer Hebel mit Schublehre), das in das Loch des Schaltauges geschraubt wird. Dieses Werkzeug hat genügend Hebel, um das Schaltauge gerade zu biegen, und besitzt gleichzeitig eine Messlehre, mit deren Hilfe man die parallele Ausrichtung kontrollieren kann.

Unterwegs kann man das Schaltauge nach Demontage des Schaltwerks mit einem Engländer geradebiegen. Dies sollte aber allenfalls als Notreparatur erfolgen.

Campagnolo Schaltwerke mit großer Gangspreizung haben absichtlich die Kettenführungsrollen nicht exakt untereinander stehen. Die Spannrolle muss etwas weiter außen angeordnet sein als die Leitrolle.

Die vier Einstellschrauben in der Reihenfolge Ihrer Wichtigkeit

derailer

Die Begrenzungsschrauben

Die Begrenzungsschrauben sind zwei Schrauben, die festlegen, wie weit sich das Schaltwerk von links nach rechts bewegen kann. Sie sind zumeist auf der Rückseite des Parallelogramms zu finden. Manchmal sind sia auch auf der Außenseite angebracht. Die Schraubenenden drücken gegen ein internes Teil des Parallelogramms, dass die Bewegungsfreiheit des Schaltwerks zur jeweiligen Richtung hin limitiert.

Die Begrenzungsschrauben sind nicht dazu da, das Schaltwerk zu bewegen, sondern stellen eine harte Bewegungslimitierung dar, wenn es durch den Schalthebel bewegt wird. Wenn man die Begrenzungsschraube löst, kann sich das Schaltwerk weiter in die entsprechende Richtung bewegen. Festziehen der Schraube begrenzt den Bewegungsspielraum in diese Richtung.

Normalerweise stellt man die Begrenzungsschrauben einmal nach der Montage des Schaltwerks ein und brauchen danach nicht wieder beachtet zu werden. Wenn man sie bei einem Fahrrad, das bisher gut schaltete, nachstellen muss, ist das ein Indiz dafür, dass das Schaltwerk (oder das Schaltauge) verbogen ist. Dieses Nachjustieren eines verbogenen Schaltwerks mit den Begrenzungsschrauben ist als Notreparatur in Ordnung, jedoch als Langzeitmaßnahme nicht ratsam.

Bei neueren Schlatwerken sind die Begrenzungsscharuben mit einem "H" (high/groß) und "L" (low/klein) markiert. Bei manchen älteren Schaltwerken gibt es diese Markierung nicht, weil man die Enden der Schrauben sehen kann. Wenn man nun in einen großen Gang (kleines Ritzel) schaltet, schaut man, welche Schraube anstößt und weiß, dass dies die "H"-Schraube sein muss. Die andere Schraube ist die "L"-Schraube.

Diese Einstellarbeiten sind nicht übermäßig umständlich. Habe keine Hemmungen, die Schraube eine halbe oder eine ganze Umdrehung zu drehen. Es gibt nur eine etwas kritische Stelle mit der Einstellung des kleinsten Gangs (L). Hier kann man evtl. das Schaltwerk so viel Bewegungsspielruam geben, dass die Kette zwischen Ritzel und Speichen fällt. Bei den drei anderen Schrauben kann es zu unsauberen Schaltvorgängen kommen, deren Auswirkungen aber harmlos sind und leicht korrigiert werden können.

1. Begrenzungsschraube L (großes Ritzel)
   Die Begrenzungschraube für den kleinsten Gang (größtes Ritzel) wird üblicherweise mit dem Buchstaben "L" gekennzeichnet. Sie hindert das Schaltwerk daran, die Kette in die Speichen zu werfen. Falls sie zu lose ist, kann das Schaltwerk die Kette über das Ritzel hinaus überschalten und sie landet zwischen Ritzel und Speichen, was katastrophale Folgen haben kann. Wenn sie zu fest angezogen wurde, schaltet das Schaltwerk nicht (oder nur sehr unwillig) auf das größte Ritzel.
2. Begrenzungsschraube H (kleinstes Ritzel)
   Die Begrenzungschraube für den größten Gang (kleinstes Ritzel) wird üblicherweise mit dem Buchstaben "H" gekennzeichnet. Sie hindert das Schaltwerk daran, die Kette über das kleinste Ritzel hinweg nach außen zwischen Rizel und Ausfallende zu schalten. Wenn die Schraube zu lose ist, macht das bei indexierten Schaltungen (außer beim Invers-Schaltwerk) nichts, weil die Zuglänge verhindert, dass das Schaltwerk über das Ritzel hinaus schaltet. Wenn die Schraube zu fest angezogen ist, ist es unmöglich oder sehr schwierig auf das kleinste Ritzel zu schalten.
   Schwierigkeiten auf das kleinste Ritzel zu schalten haben zumeist nicht den Grund, dass die Begrenzungsschraube H des Schaltwerks nicht richtig eingestellt ist. Meistens liegt es an einem verbogenen Schaltwerk oder zu hoher Reibung der Schaltzüge.
3. Indexing adjustment
   The indexing adjustment is the most frequently needed derailer adjustment. The detents (click-stops) that provide indexing are in the shifters, and the index adjustment sets the length of the cable so that the derailer is in the correct place to correspond with each click stop.
   If a derailer is correctly adjusted when it is installed, this is the only adjustment that should have to be tweaked later on, to accommodate cable stretch, or when cables are replaced.
   The indexing adjustment is an adjusting barrel located at one end of a length of cable housing. Many rear derailers have more than one index adjuster. All indexed derailers have an adjuster where the final loop of cable housing ends at the derailer itself. Many bicycles also have another adjusting barrel located so that it can be adjusted while you are riding. On mountain-bike-type shifters, this will be located at the shifter itself, just where the cable exits. On road bikes with handlebar-mounted shifters, there will usually be an adjusting barrel at the cable stop where the upper length of housing ends on the upper end of the down tube.
   It doesn't matter which of these adjustments you use: use whichever is more convenient.
   Before you try adjusting the indexing, shift to the highest gear (smallest sprocket.) Make sure that the shifter is in the position that allows the cable to be as loose as it can get. (Exception: Shimano Rapid Rise derailers work the opposite way, so you are shifting to the largest sprocket).
   Click the shifter to the first click after the fully loose position, then turn the pedals forward. The chain should shift to the second smallest sprocket. If it doesn't, it means the cable is too loose. Turn an adjusting barrel counter-clockwise to tighten the cable. Start with half a turn, then check again. It is very common for beginners to over-correct by turning the adjuster too far. Sometimes this will result in moving the indexing so far off that it sort-of works, except that the clicks are one notch off, so one of the extreme gears doesn't work properly, but the others appear to be OK. This is why it is important to check that the shift from the smallest to the second-smallest sprocket occurs in the right place on the shifter.
   Fine adjustments are accomplished according to the following principles (opposite for Shimano Rapid rise derailers)::
   • Shifting to larger sprockets is accomplished by tightening the cable; if such shifts are slow, the cable is not tight enough-- turn the barrel counterclockwise to tighten it.
   • Shifting to smaller sprockets is accomplished by loosening the cable; if such shifts are too slow, the cable is not loose enough-- turn the barrel clockwise to loosen it. If the rear indexing works properly when using the large chainwheel but not on the small chainwheel, or vice-versa, this is often a sign that the rear derailer hanger is bent.
4. Angle adjustment ("B-tension")
   Modern derailers have two spring-loaded pivots. The lower pivot, sometimes called the "a pivot" winds the cage up to take up slack as you go to smaller sprockets. The upper "b pivot" adds additional slack take-up ability by pushing the derailer's parallelogram backwards.
   The tension of the two springs needs to be balanced for best shifting.
   Most derailers have an angle adjustment screw (Shimano calls it "B-tension adjustment"). This adjusts the tension of the upper ("b") spring of the parallelogram, and thus the height of the jockey pulley. The looser this screw is, the closer the jockey pulley will be to the cluster.
   The angle adjustment will need to be set according to the size of the largest rear sprocket. If you change to a cluster with a larger or smaller low-gear sprocket, you will need to re-adjust this setting. You will also need to adjust this if you change the length of your chain.
   If the angle adjuster is set too loose, the jockey pulley will bump into the largest sprocket when the bicycle is in the lowest gear (large rear, small front). This is the gear you should check the adjustment in. A larger low-gear sprocket may require a different rear derailer, for enough angle adjustment to clear the sprocket. In extreme cases, such as with a Shimano 36-tooth sprocket, a longer angle-adjustment screw may be needed -- some people even install the screw backwards.
   Since a derailer shift is caused by forcing the chain to run at an angle, the greater the angle, the sooner it will shift. The closer the jockey pulley is to the cluster, the sharper the angle will be for a given amount of sideways motion of the derailer. Thus, the looser the angle adjuster screw is, the better the shifting will be.

Campagnoloschaltwerke

2001 and later Campagnolo rear derailers don't use a "b tension" adjustment. Instead, they have an "a tension" adjustment. Spring balancing is done with this adjustment, but in the opposite direction. That is, loosening the "a tension" has the same effect as tightening the "b tension."

Kettenlänge

If you replace your chain or sprockets, you should check your chain length. New chains come longer than they need to be for the vast majority of bicycles. You will almost certainly need to shorten a new chain before installing it on your bicycle. If your large sprocket sizes are anywhere near the maximum your rear derailer can handle, the chain length can be quite critical.

If the chain is too short, it will be at risk for jamming and possibly ruining the rear derailer if you accidentally shift into the large-large combination. Never run with a chain that is too short, except in an emergency.

If the chain is too long, it will hang slack in the small-small combinations. You should never use those combinations anyway, so this is not a serious problem. If you exceed the recommended gear range for a particular rear derailer, you may have to accept droop in these gears.

The best technique for setting chain length is to thread the chain onto the large/large combination, without running it through the rear derailer. Mesh the two ends on to the large chainwheel so that one complete link (one inch, -- one inner and one outer half-link) overlaps. In almost all cases, this will give the optimum length. Inner and Outer half-links must alternate: Won't Fit-Too Long Full-link overlap, correct with chain on the large chain- wheel and sprocket but not yet run through the rear derailer. Won't Fit-Too Long Overlaps by a half link. Already too short unless it could overlap by a full link as at left. Will Fit Will connect, but too short except on a bicycle with a non-derailer drivetrain.

Start with the shortest chain that would permit connection, allowing one extra complete link as shown in the photo at the left above, so the bottom of the chain droops if you align it as in the picture at the right. Then thread the chain through the rear derailer and connect it. Turning the crank by hand, check that the chain will shift to the large-large combination using the front derailer or rear derailer, or both at once, without binding.

Work by shortening the chain, rather than lengthening it. Making the chain too short, then lengthening it is a time-waster. The narrowest chains, used with cassettes that have 10 sprockets -- sometimes 9 -- must be joined using special one-time-use replacement pins or master links. You probably only get one of these with a new chain, so it is important to get the length right on the first try.

Spoke Divider Alex Ramon has a video that shows: How To Calculate Chain Length

Spoke Divider

Zustand der Kette

Chain condition will have an effect on how well your system shifts; in particular, if you chain is dry and rusty, it will not shift well, because the links will be stiff.

Chains wear out, typically after only a few thousand miles. As they wear, they elongate slightly. They should be checked regularly for signs of this sort of wear. This issue is addressed in detail in my article on Chain Wear and Maintenance.

A worn chain will usually not be the cause of shifting problems, but usually is the cause of skipping under load.

Steife Kettenglieder

If you have a regular, repeating skip or hitch every 3 or 4 turns of the pedals, you may have a stiff chain link. This is commonly the link where the chain was joined when it was installed. When the chain tool presses the pin through the chain, the head of the pin tends to pull the uppermost chain plate along with it, so that the two outer plates are squeezing together against the inner plates.

The easiest way to fix this is to bend the problem area of the chain into a "Z" shape, with the bad joint on the diagonal part, then flex the chain back and forth from side to side. This will slightly spread the tight plates, and free up the link.

A link that has been bent in a chain-jamming incident can cause similar symptoms. Generally, the bent link (or the whole chain) will need to be replaced.

The easiest way to spot stiff/damaged links is to shift the bike into the small/small gear (the gear you should never actually ride in.) This gear has the chain at its slackest, and flexes it farther than any other gear, as it goes around the small rear sprocket and the derailer pulleys. Slowly backpedal while watching the chain as it feeds through the rear derailer, and you will usually be able to see the bad link jump.

Einstellen des Umwerfers (vorne)

There are different front derailers for different seat-tube angles, different-sized chainwheels, two or three chainwheels, and in some cases, different shifters. See my article on front derailers for details.

The front derailer should not be adjusted unless the rear derailer is already working properly, because front derailer adjustments are affected by the position of the rear derailer, and you will need to access all of the rear sprockets to adjust the front derailer correctly.

Front derailer adjustment is not an exact science. It requires a good eye and a bit of patience to get right.

When you apply power to the pedals, the power is transmitted to the rear sprockets by the upper run of the chain. The lower run of the chain is just the return path, and the only tension on the lower run is applied by the spring in the rear derailer. Since the front derailer does its shifting with the upper, power-transmitting, section of chain, it has a harder task. In general, you should not expect a front derailer to shift well while you are pedaling hard, even if the rear derailer does.

Einstellmöglichkeiten des Umwerfers

1. Chain slope and derailer selection
   On a bicycle with a small rear wheel, high bottom bracket or steep seat tube, the chain slopes down more toward the rear wheel, and the chain cage of the front derailer needs to sit farther to the rear. Instructions for many clamp-on front derailers specify a range of angles. The front derailer of some bicycles attaches to a special slotted tab, which may be brazed, bolted or glued onto the frame. The tab limits the range of chainwheel sizes that can be used, but it can be aligned ideally for the particular bicycle. Another solution is a Shimano E-type front derailer, which attaches to the bottom bracket, so it can be rotated to any needed angle --though it can be used only with the particular chainwheel sizes for which it is designed.
2. Clamp Position
   The most critical adjustment of a front derailer is its attachment to the bicycle frame. This must be set correctly before you attempt to adjust the limit stops. All derailers except the E-type derailer allow two adjustments, for angle (as seen from above) and height.
   • Angle
     of the front derailer is judged by looking down on the cage from above. Modern front derailers have very subtly shaped cages, so it is not always easy to tell when the ideal adjustment has been made. In general, the centerline of the cage should be parallel to the centerline of the frame. Rotating the derailer so that the back of the cage is farther out will sometimes improve shifting to the small ring of a triple by preventing overshifting, but may cause increased need for trimming on the larger rings. It may also cause the crank to strike the cage.
     Rotating the derailer so that the back of the cage is farther in will help reduce the need for trimming on the large chainwheel, and will provide crisper downshifting, but with a greater tendency to overshift on the inside. This may be appropriate on bicycles equipped with an anti-derailment device.
   • Height
     of the front derailer is a principal factor in how well it will shift. Manufacturers commonly recommend 2 mm clearance between the bottom of the outer cage plate and the teeth of the large chainwheel. This is a bit of an oversimplification. Best performance will result from the very lowest position that still just barely keeps the cage from hitting the chainwheel teeth. The lower you can get it, the better it will shift, and the less you will need to trim the front derailer.
3. Derailer/Chainwheel Mismatch
   To get the front derailer as low as possible, the curvature of the outer cage plate has to match the curvature of the largest chainwheel.
   If you use a larger chainring than the derailer was designed for, the rear of the cage will hit the teeth of the big chainring before the front of the cage gets low enough to provide crisp shifting without the need for trimming.
   If you use a smaller chainring than the derailer was designed for, it will shift OK, but you'll have to do a fair amount of trimming, due to the rear of the cage being higher than it should be, so that the chain crosses through it farther back.
   Lately I've started modifying front derailers for improved shifting with larger rings. I have a Shimano RSX front derailer on a bike with 50/38/28 Biopace (the sweep of a 50 Biopace is comparable to that of a 52 round.) The RSX front derailer works great on its intended 46/36/26 setup, but the cage doesn't match the curve of the larger chainring. In a couple of minutes with a grinding wheel, I removed a good bit of metal from the bottom rear of the outer cage plate, and a bit from the bridge section where the inner and outer cage plates connect at the back. This made the derailer match the curvature of the larger chainwheel, and allowed me to set it low enough to provide good chain control. This setup now works fine with an STI indexed shifter that doesn't permit "trimming" the front derailer.
4. Low-gear limit stop.
   The low-gear limit stop stops the derailer from shifting past the smallest chainwheel and throwing the chain onto the bottom bracket shell. If the stop is too loose, the chain will fall off when you try to downshift to the small chainwheel. If too tight, you will find it difficult or impossible to shift down to the small chainwheel.
   On older front derailers, the low-gear stop is the one closer to the frame. Many newer designs reverse this position for reasons relating to the mechanism used.
   The basic adjustment for the low-gear stop is to set it so that the chain just barely clears the inner plate of the cage when the lowest gear (small front, large rear) is selected. This will usually be the best position for double-chainwheel setups, and will permit the use of most or all of the rear sprockets with a minimum of trimming.
   For triple chainwheels, it will sometimes be necessary to adjust the low-gear stop a bit looser, so that the outer plate of the derailer can travel far enough to knock the chain off of the middle ring.
   • Anti-derailment devices
     In some instances, you may find that one adjustment of the low-gear stop causes the chain to derail past the small chainring, but a tighter setting results in slow downshifting to the small ring.
     In such cases, a good, if inelegant, solution is sometimes to install an anti-derailment device that clamps to the seat tube. These products, such as the 3rd Eye Chain Watcher ® and the N-Gear Jump Stop ® set up a barrier preventing the chain from overshooting the small ring, no matter how loose the low-gear stop is set. This allows the low-gear stop to be set to allow the derailer to move farther inboard for faster, more precise shifting, even under some load. These devices can often save the day when extra-wide range gearing is used on a mountain bike or tandem.
5. High-gear limit stop
   The high-gear limit stop is pretty straightforward. It should be set so that the chain almost rubs on the outside plate of the front derailer cage when the bicycle is in its highest gear (large front/small rear). This will reduce the need for trimming as you shift the rear derailer.
   If the shift to the large chainwheel is slow, make sure that you aren't pedaling too hard: front upshifting requires being ready to have the cranks slow down when the shift takes place. If the shift is unreliable even when you are pedaling lightly, you may be able to improve it by loosening the high-gear stop a bit. If you do so, check to make sure that the derailer cage is not moving so far out that it can be struck by the crank as it goes by.
   Sometimes front upshifting may be improved by rebending the front edge of the inner cage plate outward a bit. This may be done with an adjustable wrench. This is rarely necessary on modern front derailers, but used to be a very common trick on older, cruder designs.

Umwerfer trimmen

As you shift the rear derailer one way or another, the direction from which the chain runs from back to front changes a bit. As a result, sometimes it is necessary to "trim" the adjustment of the front shifter after changing gears with the rear, even if you are staying on the same front chainring. Trimming means using the shifter to move the front derailer cage sideways just a little bit, enough to stop the chain from rubbing, but not enough to make it shift to a different chainring.

Older front derailers designed for friction shifters used to require trimming as a matter of course, but newer indexed systems can often be set up so that no trimming is necessary.

For a "trimless" front indexing, you will usually need to be using the particular chainwheel sizes for which the front derailer was designed, and the chainwheels must not be bent even a little bit. The lower down the cage is mounted, the less trimming will be needed.

[The SunTour Symmetric shifter -- from around 1982, non-indexed -- was designed to trim the front derailer when the rear derailer was shifted. Notice how the front shift lever moves forward and backward as the rear shift lever is rotated on the video clip below. Remarkably, no other shifter system since has incorporated this feature. I thank N. Keith Duncan for this video clip. -- John Allen]

If your system requires trimming, it is essential that you do it. If you ride with the chain rubbing against the front derailer cage, you will wear a groove in the side of the cage and it will never shift properly. See also my Front Derailer Selection Article

Kettenlinie

"Chainline" refers to the sideways distance of the chain/sprockets from the centerline of the bike.

Front shifting problems are frequently related to incorrect chainline, that is, the chainrings are either too close in, or, more commonly, too far away from the bike's centerline.

This generally is the result of having the wrong bottom bracket for the particular crankset model in use.

This site has a separate major article on Chainline

Züge

More often than not, shifting problems are due not to any problem with the derailers, but to excessive friction in the cables that control them. The usual effect of cable friction is to make the derailer move sluggishly when the return spring is pulling it toward a smaller sprocket.

The most common area for this problem is the short loop of cable housing that leads from the rear stay to the derailer. The front end of this housing is exposed to road spray from the front tire, and the resulting rust can seriously degrade shifting. This cable loop should be fairly long, so that it makes a very gradual curve. Many bikes have too short a housing loop here.

Another problem area is the cable guide where the cables run under the bottom bracket. In addition to sluggish upshifting, friction in this area can cause spontaneous upshifting under load.

Cable housing for indexed shift applications uses multiple straight wires sandwiched between plastic, instead of the spiral-wound wire used in brake cable housing. This requires a fairly special tool to cut properly. When you buy such housing, you would do well to have exact length information so that the shop that sells it to you can cut it for you, if you don't have a suitable cable cutter.

When you cut housing, the plastic liner gets squished a bit. It is helpful to clean and round out the opening with an awl or scriber.

The final loop at the rear derailer is short and has a nearly 180 degree bend. "Compressionless" housing is normally used for this. I've taken to bending the piece of housing to the approximate shape it will be used in before cutting it.

If you cut the housing straight, all of the longitudinal wires come out the same length, so when you bend it, the end of the housing acquires a slanted face, since the wires on the inside of the bend have a longer way to go around the curve. It is my belief that cutting the housing while it is bent makes a smoother, more reliable connection at the end of the housing. You must have a ferrule at each end of each piece of housing. This helps keep the hole in the housing aligned with the cable stop, and also keeps the housing from falling apart.

With modern, lined housing, greasing the cables is no longer necessary. In fact, it makes things worse, due to the stickiness of the grease. A bit of medium oil on the section of cable that runs through the rear loop to the rear derailer will help retard rust, though.

Cables and housing come in a wide range of quality. I recommend buying only premium-grade cable and housing.

For problem installations, super-premium cables, such as Gore Tex ® will help. There are also some situations where the spring tension of the rear derailer is just insufficient to overcome the cable friction. SRAM (Grip Shift ®) used to make a product called a "Bassworm ®" which seals the rear housing loop and supplies spring assistance to the cable at this point. I have another major article on cables at this site, covering these issues in more detail.

Erneuern der Züge

To replace a derailer cable, you want to start out with both the derailer and the shifter in whichever position has the cable slack. This will usually be the position corresponding to the smallest chainring/rear sprocket.

If you disconnect the cable (or if it broke) and pedal the bike a couple of times the derailer will automatically go to the correct position.

For the shifter, you may need to pull on the end of the cable while operating the shifter to get it to shift to the loosest position. If the shifter indexes, it will stay in that position. If it is a friction shifter with a return spring, like most handlebar-end shifters, you may have to tighten the friction adjustment to get the shifter to stay in the loosest position.

Once the derailer is disconnected from the derailer's anchor bolt, pull the housing (if any) away from the shifter, and then push the exposed inner cable into the shifter. The moulded end of the inner cable should then pop out of the shifter. If it's a simple lever shifter, such as a down-tube or bar-end shifter, the cable end is readily visible.

If it's a more complicated ratcheting type shifter, there will usually be an access hole where the cable end can pop out...but his access hole may only line up correctly if you remembered to shift to the loosest gear position first.

Twist-grip shifters such as SRAM GripShift are typically the most difficult for cable changing, and these commonly require disassembly.

Generally, the derailer limit stops should not require any adjustment when you replace a cable, but you will need to adjust the indexing.

Before connecting the cable, screw the adjusting barrel all the way in, then back it out maybe a turn or a turn and a half. This will give you the opportunity to loosen the cable a little or to tighten it a little or a lot.

Erneuern des vorderen Zugs

Thread the cable through the shifter and any housing. Check the condition of the housing and particularly the open ends. Replace or trim if needed. See also my Cables Article. Pull on the cable and operate the shifter until you have the slackest position. The chain will normally be on the smallest chainring.

Run the cable under the anchor bolt hardware and secure it. If it's an indexing system, and particularly with triple chainrings, you will need to fine-tune the indexing to get it to shift well and run smoothly on the middle chainring.

Erneuern des hinteren Zugs

Thread the cable through the shifter and any housing. Check the condition of the housing and particularly the open ends. Replace or trim if needed. See also my Cables Article. Pull on the cable and operate the shifter until you have the slackest position. The chain will normally be on the smallest rear sprocket.

Methode A

Use a pair of pliers to pull the cable really tight and secure the anchor bolt. Use the adjusting barrel to correct the indexing adjustment.

Methode B

(This is how I do it. Only works if you have the bike in a work stand of some sort, unless you have three hands.)

Hand pedal forward with your right hand while manually pushing the rear derailer inward until the chain engages the 3rd smallest sprocket. Stop pedaling, then let go of the derailer. The derailer spring will try to move the derailer outward toward the smallest sprocket, but the stopped chain won't let it go all the way.

Pull fairly firmly on the end of the cable to take up the slack and secure it with the anchor bolt. Then you can pedal and check the indexing adjustment. I find that this usually gets me quite close, with only a minimal amount of fine tuning needed to the indexing adjustment.

Zugklemmung (hinten)

One area that commonly causes problems is the attachment of the inner cable end to the derailer's anchor bolt. If this comes in at the wrong angle, it can change the geometry of the parallelogram and make it impossible to get the derailer to index properly across its range.

There is usually a groove in the derailer body or a washer with a bent corner to determine that the cable is running correctly.

Alternative Zugführung

Two alternate cable routings for Shimano derailers adapt them for use with nonstandard shifters or cassettes.

Shimano originally publicized an alternate cable routing which placed the cable slightly closer to the pivot, making the derailer move slightly farther for each click. This adaptation makes newer Shimano derailers work with older Dura-Ace shifters, but it is also useful when you want to use a 9-speed cassette with 10 speed shifters, or 8-speed cassette with 9-speed shifters, or a 7-speed cluster with 8-speed shifters. You may need to fine-tune the amount the cable deviates from the standard position, so the derailer sweep matches the sprocket spacing.

cable routing to increase derailer travel

The other alternate cable routing, suggested by Brian Jenks, proprietor of Hubbub Cycles, decreases the derailer travel for each click. This makes some Shimano derailers and shifters compatible with Campagnolo cassettes. It is also useful when you want to use a 10-speed cassette with 9-speed shifters, or 9-speed cassette with 8-speed shifters, or an 8-speed cassette with 7-speed shifters. You will then lose the use of one sprocket, unless you are using a shortened cassette such as an 8 of 9 on 7, or 9 of 10 on 7. Note the two tabbed washers in the drawing below -- one to change the cable routing, and the other to secure the cable. Again, you may need to fine-tune the cable position.

cable routing to increase derailer travel

Unlike the Dura-Ace modification, the Hubbub modification is nonstandard, and not all of the ratio changes are accurate. Chris Juden of the Cyclist Touring Club (U.K.) has posted a Web page listing usable combinations. Pulley-type adapters from JTek Engineering offer a more precise alternative.

Zugklemmung (hinten)

Some newer front derailers are designed with a choice of two cable attachment options. If the cable is run on the outside of the anchor bolt, away from the parallelogram pivots, the cage moves less far for a given cable movement, providing a lighter action, and easier fine trimming.

If the cable is run on the inside of the anchor bolt, toward the parallelogram pivots, the cage moves farther for a given cable movement. This is often necessary to provide correct functioning with indexed shifters.

Springen/selbstätiges Schalten

Do your pedals sometimes jump forward when you pedal extra hard? This is a common complaint, especially when a rider stands up to pedal. Indeed, this dangerous condition is one very good reason for remaining in the saddle and spinning in your lower gears, rather than standing up and pumping in a higher gear.

Although jumping/skipping/autoshifting is often blamed on the derailer, it is only very rarely the result of a derailer malfunction.

This jumping may be one of two totally unrelated problems: skipping or autoshifting. The first step in troubleshooting this problem is to determine whether the problem is simple skipping or autoshifting.

• Skipping involves the chain jumping over the tops of the sprocket teeth under load. After the chain jumps, it remains on the same sprocket. This is usually caused by wear to the chain and/or the sprockets, and is most likely to happen on the smaller rear sprockets, especially if they are used in conjunction with the small chainwheel in front. This issue is addressed in considerable detail in my article on Chain Wear.
  A form of skipping, not necessarily under load, sometimes also results from stiff links.
• Autoshifting feels just like skipping, except that after the jump you find that the rear derailer has shifted up to the next smaller sprocket. Autoshifting is commonly caused by a combination of frame flex and cable friction. The mechanism of this is explained in detail in a separate article on Autoshifting.

As you can see, there is a lot to be done to get the most out of your derailers. Buying a more expensive derailer is usually not the solution to shifting problems. The actual performance of your system will depend much more on how well the system is set up and adjusted.

There has been more improvement in front derailers than in rears. If you have an older front derailer, and it is not giving satisfactory performance, you may benefit from a replacement. Beware, however, because older front derailers were designed to work with a wide range of chainwheel sizes, while new models are optimized for particular ratios, and may not work well with your crankset.

Quelle

Dieser Artikel basiert auf dem Artikel Derailer Adjustment von der Website Sheldon Browns. Originalautor des Artikels ist Sheldon Brown.