How to Change Rear Sprocket on BMX Bike? [8 Easy Steps to Do It]

When you’re riding a BMX or a single-speed bike regularly, it is essential to know that you’ll have to replace your sprockets. When you begin to notice and hear a clunking noise to your BMX, especially when pedaling uphill, you should immediately take action and get some replacement freewheel.

BMX bikes require a small single-sprocket freewheel to make your rear wheel work on the road. As you get more proficient in BMX riding, it is highly suggested that you must replace the rear sprocket with a different gear ratio.

Besides, your rear sprocket might also need some replacing as the inevitable wear and tear would show over time. Hence, you would have to learn to remove your BMX sprocket independently. In this article, we will guide and teach you how to change the rear sprocket on your BMX bike.

Step 1: Removing the wheel

The initial step to rear sprocket replacement is to remove your wheel first. As you pull the tire from your BMX bike, you should eventually fit the freewheel remover into the cog and check if it would align the four notches.

Step 2: Check if your wheel has a freehub or a freewheel system

As you choose the necessary replacement tools, consider that you should first identify which of the two types of the wheel – a freehub or a freewheel, is installed to your BMX (unless it is already determined prior). Depending on the rear hub you have on your bike, note that one or the other system is used.

Freehub contains an installed cassette holder combined with a spline and a ratchet system, enabling better precise machining. On the other hand, the freewheel type carries a cluster of sprockets with a ratcheting mechanism for free backpedaling and coasting. At the same time, it locks when you turn your pedals forward.

Additionally, you should pay precise attention when purchasing or changing your rear sprockets. Hence, you already know which would fit your riding ability. Freewheel is installed in the rear hub, while freehub glides onto your bike’s hub splines, where it is stored with a unique lock ring.

Step 3: Collect and assemble the appropriate tools

Pick up your adjustable wrench and choose a big one or the size that would fit your freewheel or freehub key’s nut. The next thing you should get is copper grease. Any grease available in your garage should do in the absence of copper grease. However, it would be best to use copper grease for the application. Then, a cotton cloth or maybe a spare kitchen paper wipes as an alternative.

If you have a freewheel BMX system, you need a key for freewheel removal, while a cassette lock nut key must be used if you have a freehub. 

While freewheel keys can fit the cassettes, they would not fit the splines deeply enough due to their smaller “teeth.” Hence, it could have a more significant impact, such as damaging the interface, so it is better to use a cassette key instead.

Lastly, you would also be required to get a chain whip to counter and prevent the cassette from rotating when you disassemble the lock ring.

Step 4: Attaching the freehub or freewheel into place

In the assembling procedure, ensure that the freewheel key slithers fine over the freewheel splines. If the key could not slide in, it may indicate that the axle must be turned slightly (about a quarter), or a lock nut that holds the cones needs to be taken out from that edge.

Step 5: Unscrewing

There could be two different procedures for removing and unscrewing BMX rear sprockets. 

For the freewheel unscrewing, it is better to mount your sprocket’s key into the vice as you confirm that it slid easily, as referenced in Step 4. You should double-check if it is in a horizontal position and firmly held in place to ensure that the splined part sticks out. Next, you must deliberately put the wheel onto the splines and guarantee that it is well seated.

For the freehub screwing, once a cassette key is installed, you should place the wheel on the ground to ensure that the cassette is facing your front view. Then wrap the chain whip near the right-hand side, accompanied by a wrench clamping and turning into the left side of the cassette.

Step 6: Mounting

Wash the rear sprocket threads on the hub and the freewheel. Then get your copper grease and put it into the hub threads for the mounting. While you can use an alternative grease at hand, find a copper grease as much as possible since it will help prevent your rear sprockets from being stuck when it requires another change next time.

Delicately screw your sprockets onto the hub and then confirm if it is parallel and goes on smooth and refined. If you observe resistance in motion, there is cross-threading, and it is not mounted in parallel. In that case, use your key for the unscrewing, and it should turn quickly; if not, do it all over again. 

Once it reacts finely and smoothly, you can now screw it all the way. Use your hand to tighten its grip, but be careful not to cut the palms on the sprocket teeth. You can do this step with the help of cloth or gloves. Besides, it would further be tightened when you start pedaling your bike.

Smudge some of your copper greases onto the lock nut threads and the area where it presses the sprocket, then carefully try to screw it using your hand. After that, you can do some visual checking to see if it is all seated properly.

Step 7: Refitting

Penultimately, using a lock ring key and a wrench, you should secure the lock nut in its position to seize torque. Then, you must refit the sprocket remover into place and use a spanner to secure the rear sprockets in its place.

Remember that you do not have to use extreme force at this point, as the sprockets will automatically tighten when you try to pedal your BMX bike. 

As the threads are moderately greased, you must refit the nuts and put the tires back on your bike. You can now ride your BMX bike to secure the sprocket position further.

Step 8: Test if you tightened the lock ring enough

Lastly, make sure that you conduct a final tightening of the cassette lock ring with a lock ring tool. The typical and standard torque setting is at 40Nm. It would be best to tighten it until you can feel the serrations on the lock ring’s inner face binding with the serrations on the outer part of the smallest sprocket.