If you spend enough time around bikes, eventually you are going to need to replace a chain. It will wear out, get rusty, bent, or break. Chain replacement is not hard, but it does require a special tool called, appropriately enough, a “chain tool”. You can pick one up for about $5 – $10. You’ll also need a new chain. To find the correct length, count the number of gears on the cranks and rear wheel of your bike. Replacement chains are sold based on a range of gears or speeds they can accommodate. Multiply the number of front gears by the number of rear gears to find out how many speeds your bike has. For example, if you have 2 in the front, and 6 in the back, you have a 12-speed bike.
To do the job correctly, it is helpful to understand how a bike chain works. Unlike your typical chain made up of linked loops, a bike chain is designed to mesh with a set of gears, and run smoothly through a series of guides that allow you to shift from one gear to another. To accomplish this, it has a flat profile made up of 2 plates per link, connected with pins. In this respect, it shares more in common with a metal watch band than an anchor chain. The pins are what meshes with the gears, allowing you to transfer power from your feet to the wheels.
Now that you understand how your bike chain is put together, begin the replacement by setting your shifters so your chain is on the smallest gears front and back. If your bike is not ridable, you can get the chain on the proper gear by flipping your bike over or getting someone to hold up the back end, and then turn the cranks with one hand while shifting with the other. If your chain is broken or jammed, you can skip this step. It makes removal and replacement easier, but is not essential.
Now before going any further, take a few pictures of how your chain winds through the derailleurs (the guides near the gears that move the chain when you shift). This will give you a reference so you can make sure to reassemble it correctly later.
Got those photos? Ok, now remove the tension from the existing chain by pushing the rear derailleur arm forward, which will allow you to lift the chain off the rear gear set. Now, grab your chain tool, which resembles a miniature vice. Its purpose is to push out the chain pins and separate the links of the chain. Use it to remove any convenient pin, then slip the separated chain out from the bike.
Lay the chain out on your garage floor. Line it up with your new chain and measure out the number of links. You must use the exact same number of links on the replacement chain or your gears will not work properly.
Again, using your chain tool, remove the pin on your new chain that mirrors the one removed on your old chain, so you end up with the same number of links. You may also need to remove a pin at the opposite end of the chain, depending on how it was packaged. If the opposite end is already “open you don’t need to do this.
Some chains also come with a “quick link”. In this set up one pin is fixed in place to each plate making up this special link. The other end of the plate has a slotted hole, so when the plates face each other, the pin fixed to the opposite plat can fit in the opposing hole. When tension is applied to the chain, the pins lock into the slots, securing the chain.
Once you have the correct length of chain, re-route your chain around the front gears and through the derailleur set, checking your photo to make sure you’ve done it correctly. Re-connect the ends of the chain using the pin removed from the new chain. Use your chain tool to push it back in place. (or link together your quick release link). Take the tension off again by pushing the derailleur arm, and loop the chain over the smallest front and back gears. Slowly release the derailleur arm while making sure the chain stays in place. Give the crank a few turns to ensure everything is moving properly. Then try shifting front and back while hand cranking, watching that gears change correctly as well.
If your chain came pre-lubricated you’re done. If not, follow the oiling steps in my blog on basic bike maintenance. You are now ready for your next ride!
Bonus Tip!: When ever working on a bike chain, you are going to encounter grease. Wear work gloves or rubber gloves to keep the grease off your hands. Forgot to do this? Clean up with some WD-40 sprayed on a paper towel. You can scrub till your blue in the face with soap, but the WD-40 will get it off almost instantly.