How to: Replacing the MTB Chain

To remove your old chain, it is best to shift your bike to the smallest sprocket. If the chain is very dirty, you can clean it simply by turning the crank backwards and sliding the lower chain strand through a rag. Keep turning until the master link is at the bottom. If your chain doesn't have a master link, it doesn't matter where you stop. With a SRAM rear derailleur you can now push the rear derailleur cage forward and lock it with the small cage lock button to take the tension off the chain. Current Shimano rear derailleurs have a lever at the cage pivot point that allows you to greatly reduce tension by flipping it to the right. In both cases, this simplifies the following steps. You can now simply break a master link with master link pliers and remove the chain from the rear derailleur. If your chain does not have a master link, go ahead and grab your chain tool. Use it to drive any pin out of a chain link far enough that allows you to take the chain apart.

In order for the drivetrain to function properly with your new chain, having the correct length is important, i.e. the right number of chain links. If the chain is too short, the rear derailleur cage could be overstretched when you shift to the largest sprocket or when the rear triangle suspension compresses. In extreme cases, the chain could break or the rear derailleur could be damaged. If, on the other hand, the chain is too long, the rear derailleur loses so much slack when shifting to the smallest sprocket that hardly any tension is applied and the derailleur pulleys get too close to the cassette. This also makes the chain rattle loudly off-road. You have several options for determining the right chain length:

Use the length of the old chain:
The simplest method is to adhere to the length of your old chain. You could measure it or count its links. However, it is quicker if you lay the new and the old chain in full length parallel on your workbench (or the floor) or hang them side by side with the help of a thin screwdriver or an old spoke. Because of stretch, the chain links will not be congruent at the end, but the correct length can usually be easily identified by the offset between the inner and outer link plates. Mark the appropriate length on the pin of the new chain.

Re-determine the chain length:
Alternatively, you can just re-determine the chain length. Since the technical details of the gears play an important role here, we recommend that you follow the manufacturer's instructions. If it offers a guide for calculating or determining the chain length, then you would be well-advised to use it. If you cannot find a description, then shift your rear derailleur under the largest sprocket, place the chain on this sprocket and on the (largest) chainring and thread it through the rear derailleur cage as described in step four. Now pull the two ends of the chain towards each other at the bottom until the rear derailleur is almost completely stretched through and mark the pin where the chain has to be cut to length so that the tension is the same after connecting with a master link or rivet pin. Note, however, that the chain can only be shortened every two links or every three pins, as you can only connect inner links with outer links. When in doubt, one link longer is usually the better option. If you’re working on a full suspension bike, you should also deflate the shock (tip: write down the air pressure beforehand) or remove it temporarily to be able to check how far the distance between chainrings and cassette shifts. A longer chain is usually necessary when the suspension travel is fully utilised. You should determine the length where the distance (or chainstay length) is greatest.

When shortening the chain, it is important that the two ends fit together. When using a master link, your chain needs two ends with inner plates. The master link itself replaces the connecting outer plates. If the chain is to be riveted with a pin, one side must end with inner plates and the other with outer plates. For chains that are designed for this purpose, leave the existing end with the outer plates as it is and shorten the other end. Shortening is done with a chain tool. Going by the chain length you have just determined, use it to push out a pin at the marked point and then remove the excess links.

To fit the new chain on your mountain bike, place it on top of the smallest sprocket of the cassette and thread it anticlockwise downwards and over the upper derailleur pulley into the derailleur cage. Pay attention to whether the manufacturer of the chain specifies a running direction. This refers to the direction of the chain’s movement as you pedal. On the way to the second derailleur pulley, thread the chain past the small bar in the rear derailleur cage so that it does not rub against it later. Go around the lower derailleur pulley to the left – anticlockwise. Now you can put the other end of the chain over the chainring and bring both ends together at the bottom. You can hold the chain together loosely with a chain hook so that you don't have to keep it taut all the time while trying to insert a master link or position the chain tool. Some chain wear indicators have this function directly integrated. Likewise, some chain tools include a wire bracket for this purpose. Alternatively you can also bend an old spoke yourself. In the last step you connect the two ends with either a master link or the chain rivet.

Master links usually consist of two identical halves. You insert one with the pin from the front into one end of your chain, and the other from the back into the other end. If necessary, pay attention to the chain’s running direction here as well. If there is an arrow on the master link, it indicates the direction the chain moves in when pedalling. If you hang it at the bottom, the arrow should point in the direction of the rear derailleur. If the master link is shaped differently at the top and bottom, please follow the manufacturer's instructions on how it should be installed. Then hook the two halves together. Make sure that both tabs are securely seated in the grooves of the pins! To engage the master link, you can slowly turn the crank backwards until the master link is in the upper run. Now block the rear brake and briefly apply a little pressure to the front or bottom of the pedal. You can usually hear and feel the master link engaging. The two halves form a positive connection, which is why this mechanism only works once on many master links. Pay attention to the manufacturer's instructions regarding whether your master link may be taken apart and put back together repeatedly. Take a quick look at the result and see if the chain can move normally at the clasp. Finally, you can "switch on" the tension on the rear derailleur cage again and shift through all gears once on the repair stand.

Chains that are fitted without a master link usually include a slightly longer chain pin. Take the two ends of the chain and bring them together so that you can put the rivet pin through them both, pointy end first. Then you take the driver on the chain tool and insert the joint in the position intended for the type of chain (i.e. 12-speed, 11-speed, etc.). By turning the tool, slowly push the chain pin into the chain with the driver until it is flush with the chain link plate like the neighbouring pins. Make sure that the pin is straight and not tilted. You can now turn the chain tool back a little and remove it. You can simply break off the part of the chain pin that sticks out on the back of the chain. Many chain tools have a small recess for this purpose, but a set of pliers will also suffice. Then check whether the new connection can be moved freely. If the riveted area is a bit stiff, you can carefully put some weight on the chain crosswise with both hands. If this doesn’t help, applying tiny amount of pressure with the chain tool on the other side of the new chain pin will do the trick. Before you start your next ride, you should reactivate the tension on the rear derailleur, shift through all the bike’s gears on the repair stand and make sure that everything runs smoothly.