How to: Replacing the MTB Chain
Is the chain on your MTB worn out? Do you want to fit a new one? No worries. We’ll explain how you can replace your chain on your bike.
How to – MTB Shifters & Derailleurs: Adjusting the Rear Derailleur
Whether you’re using Shimano or SRAM, adjusting the derailleur on a mountain bike or e-MTB is not difficult. With our tips, every gear will shift smoothly.
Knowing how to adjust a modern derailleur on a mountain bike is not only practical when you're installing a new drivetrain, but can often be very helpful when you're on the go. This is because falls or component wear can sometimes make it necessary to readjust your shifters and derailleurs. Since on most mountain bikes and e-bikes the gears are only changed at the rear – with the rear derailleur – adjustment has even become easier in recent years. We therefore limit our instructions to 1x drivetrains. Whether you ride with a Shimano or SRAM shifting system is basically irrelevant for adjustments. Changing the settings of the rear derailleur differs mainly in where you find the adjustment screws. These instructions apply to mechanical drivetrains from both manufacturers. We devote a separate article to the special features of adjusting electronic gear shifters.
Basically, you adjust the rear derailleur with three parameters:
- the cable tension,
- the rear derailleur stops and
- the chain wrap.
We explain what this is all about and how you can make all three parameters work in harmony.
To ensure that your rear derailleur always shifts precisely, you need to maintain it over time. We’ll show you how.
In addition to readjusting the stops, you should also clean the derailleur pulleys from dirt from time to time or replace them with new ones if necessary.
Prerequisites for Well-Functioning Shifters & Derailleurs
In order for your rear derailleur to function as it should, some parameters must fit all-around. First off, all parts should be compatible with each other. The rear derailleur and shift lever should not only come from the same manufacturer, but also be designed for the same number of gears. This number should correspond to the sprockets of your cassette and match the width of the chain. In addition, there are a few less obvious but very important factors influencing the shifting quality. We've compiled a short checklist of what these factors would be:
- Derailleur Hanger: The derailleur hanger should be exactly straight, and the rear derailleur should be firmly screwed into it. If it is bent after a fall or hitting a rock, it is often no longer possible to adjust the gears properly. Then you should replace it or have it repaired. For precise assessment, a control gauge or an alignment tool helps.
- Shift Cable and Cable Housing: The shift cable should be routed in the largest possible radii and without kinks. The inner cable and especially the cable housing wear out and are then often the cause of imprecise shifting. Simply threading in a new inner cable usually doesn't help – new cable housing is usually needed. Pro tip for new cable housing: Use a little sandpaper to sand the ends of the cable housing flat after you have shortened it to the right length and before you put on the end caps. Simply place the sandpaper on a table and rub the end of the cable housing vertically against it until it is smooth and straight. This brings even more precision to the system.
- Care and Lubrication: Coarse dirt on the sprockets, the derailleur pulleys and generally on the rear derailleur can cause problems. A thorough cleaning with the help of special sprocket brushes or an old toothbrush can remedy the situation. A well-lubricated chain also shifts more smoothly than a squeaky dry one.
- Cassette and Chain Wear: A common cause of a sticky or jumpy gears is component wear. With too much play in the chain on the sprockets and worn-out shift aids, it will be impossible to adjust your gears smoothly. Be sure to also check the derailleur pulleys on your rear derailleur. They can also wear out and should be replaced when they are visibly worn and no longer guide the chain precisely.
- Correct Cassette Assembly: The cassette should be firmly screwed onto the freehub body. If individual sprockets or the entire cassette wobble sideways, then the lockring has probably loosened or the freehub body is not correctly seated on the hub.
Here you can see all adjustment hardware at-a-glance. © bc GmbH
H-bolt: The Limitation of the Rear Derailleur to the Smallest Sprocket
The pivoting range of the rear derailleur can be limited in both directions with end stops. The correctly set limit towards the dropout – i.e. in the direction of travel on the right – prevents your chain from becoming jammed between the smallest sprocket and the frame. Colloquially, the term "lower stop" is often used, as it refers to the lower, smaller part of the cassette. Shimano and SRAM, on the other hand, refer to the limit screw as the "high limit screw" and often mark it with an "H" because the rear derailleur is in the highest position there and at the gear with the highest gear ratio. If the bolts on your rear derailleur are not marked, check the manufacturer's documentation to see which one does what. This initial adjustment works best when no Bowden cable and no chain have been fitted yet. If you only want to check or readjust the limit, you can also do this with a chain and cable. Shift to the smallest sprocket, bearing in mind that the basic tension of the cable can also limit the movement of the rear derailleur. To adjust the limit with the H-bolt, look at the rear of the rear derailleur and place the upper derailleur pulley (the guide pulley) exactly under the smallest sprocket by turning the bolt. You will notice immediately whether you are on the right screw. Turning clockwise moves the shifter to the left and turning counterclockwise moves it to the right.
If you turn the stop to the right, the cage moves towards the wheel and vice versa. © bc GmbH
The Shift Cable Clamp
If you install a new shift cable and new cable housing, then the cable clamp is part of adjusting the shifters and derailleurs. On the shift lever, the inner cable comes out through a screw which you can use to adjust its tension. First turn this screw in completely and then turn it out again a full turn. This way you make sure you have room for adjustment in both directions. Make sure that the shift lever is on the heaviest gear (i.e. the smallest sprocket). Then you can clamp the cable to the rear derailleur. Make sure that it is threaded correctly and that the cover fits properly everywhere. Hold it slightly under tension and tighten the clamp screw to the appropriate torque. Be careful with cables that have been clamped before, as they can fray and tear after a while. You can cut off the excess with a Bowden cable cutter and protect the end with an end cap.
To create tension on the shift cable, you should pull on it a little while tightening the clamp bolt. © bc GmbH
L-bolt: The Limit of the Rear Derailleur to the Spokes
Limiting the swing range of the rear derailleur towards the spokes – i.e. in the direction of travel on the left – is particularly important. Correctly adjusted, it prevents the chain from getting between the cassette and spokes and damaging your wheel. Colloquially, this is often referred to as the "upper stop" (in the upper area of the cassette). Shimano and SRAM call it the "low limit screw" and mark it with "L" – the rear derailleur is in its lowest position and at the gear with the lowest ratio.
To make the adjustment, shift into the lightest gear. If the chain is not yet installed, there's nothing in particular that you have to keep in mind. If you have already fitted the chain, be careful that it does not jump over the large sprocket. Shift gears on the work stand with attention and care. Now look from the back again to see if the upper derailleur pulley is in line with the largest sprocket. If it is closer to the spokes than the sprocket, turn the L-bolt further clockwise. Even if you carefully try to push the rear derailleur towards the wheel, it should not be possible to move it further than the sprocket. If it's blocking in front of the sprocket, you can correct this by turning the L-bolt counterclockwise.
To Move the the cage towards the wheel, turn the screw to the left. © bc GmbH
B-bolt: The Chain Wrap
If you are completely replacing your drivetrain, now is the time to fit the chain. Our instructions for swapping out the chain gives you tips on how best to proceed. The correct chain length is important for the chain wrap – namely, how far the chain engages the teeth around the sprocket. A B-screw allows you to precisely adjust the wrap and the distance between the guide pulley and the cassette. In the lightest gear, there should still be some space between the sprocket and the guide pulley of the rear derailleur, otherwise it could hook. Since modern 1x11-speed and 1x12-speed drives operate within very narrow tolerances, we strongly recommend following the manufacturer's instructions for this setting. SRAM includes measuring gauges with Eagle rear derailleurs so that you can precisely set the gap between the rear derailleur and the cassette.
The distance from the derailleur pulley to the cassette decreases when you turn the B-bolt to the left. © bc GmbH
Adjusting the Correct Cable Tension on the Mountain Bike
After you have limited the range in which your rear derailleur can operate, the next step is to fine-tune the gear changes with the help of the cable tension. To do this, shift through the gears one by one while the bike is on the work stand. Work from the lightest to the heaviest gear and then back again. If the chain does not shift to the next sprocket as desired during a gear change and instead just rattles a little and is jumpy, then you should adjust the cable tension with the help of the knurled screw on the shift lever.If you turn it inward – i.e. towards you from the rider's perspective – you reduce the cable tension.
If you turn the screw outwards (anticlockwise), you increase the tension. © bc GmbH
The rear derailleur is pulled further towards the small sprockets by the built-in spring. If you turn it outward (away from you), you increase the tension on the Bowden cable and pull the rear derailleur towards the larger sprockets. Proceed in small steps according to the grid of the screw. A quarter turn is often enough. When should you increase the tension and when should you decrease it? It's easy to tell:
- If the chain won't shift to the next smaller sprocket: reduce tension
- If the chain jumps down one sprocket too far: increase the tension
- If the chain won't shift to the next larger sprocket: increase the tension
- If the chain jumps too far up the cassette: reduce the tension
Until all gears shift up and down smoothly, it may be necessary to shift the cassette several times in both directions, making small corrections every now and then. With a new Bowden cable, it can happen that the cable stretches a bit, and the cable housing becomes wedged in the guides. This may make subsequent corrections necessary. With a little practice, you'll be able to do it even when you're on the go.
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