The sprocket set, also called cassette, is the set of toothed gears connected to the rear wheel of the bicycle; each gear is a gear, the chain that connects it to the pedals turns the sprocket set and makes the bike move. Over time, the gear teeth wear out, making it less secure to grip the chain with consequent dispersion of a lot of driving force. In the worst case, the chain can fall off, preventing you from using the bike until you fix it.
Steps
Part 1 of 2: Remove the Old Cassette
Step 1. Remove the wheel from the frame
You can do this easily by unscrewing the nuts or the quick release mechanism located on the axle, opening the brake and pulling out the wheel; at this point, you can leave the rest of the bike aside.
The chain is most likely located around the sprockets. If you have difficulty removing it, select the smaller front derailleur, find the point where the chain slips through the two small wheels of the derailleur arm (the mechanism that allows you to change gears on the rear wheel) and push it to loosen it. the tension on the chain itself
Step 2. Inspect the cassette for damage and wear to confirm that you need to replace it
You can take this opportunity to check the hub bearings and lubricate the mechanisms. If the axis moves, it means that the tapered bearings need to be adjusted and that those that are in the axis need to be changed; if you wish, you can take your bike to a specialist shop that will do these repairs. The signs that make you understand the need to change the sprocket set are:
- The chain slips or falls as you pedal;
-
You have problems with the gearbox (attention:
make sure that the front derailleur is well adjusted before changing the cassette);
- The gear teeth are visibly worn (the tips are rounded or lower on some wheels than others);
- The gears are cracked, broken or deformed.
Step 3. Remove the quick release rod
Place the wheel on a flat surface so you have easy access to the sprocket set, then pull out the quick release mechanism, a long thin stick that runs through the hub. The rod is often paired with a nut on the other end that you can easily unscrew by hand.
Step 4. Insert the release tool into the sprocket set
Replace the quick release rod with this tool, which is basically a large hex bolt with a small stick in the center; it should have a grooved ring on one end that fits into the cassette. This tool allows you to apply pressure to unscrew the element.
Some older models are not equipped with a rod and are designed to replace the nuts found on the quick release stick; you can use them normally, just unscrew the nut and insert the tool on the old rod
Step 5. Wrap the whip wrench around the larger sprocket by moving clockwise
This tool prevents the sprocket set from turning while you unscrew it and consists of a long handle to which a 30 cm long chain segment is attached and which allows you to hold the entire cassette in place. Wrap as much chain as possible around the larger gear in a clockwise motion.
- Later, to loosen the nut, you will need to turn it counterclockwise, applying opposite pressure to hold everything in place.
- Alternatively, you can only use a long enough piece of chain.
Step 6. Engage a large adjustable wrench on the release tool you inserted into the hub, but do not move the whip wrench
If this is your first time doing this work, it may be easier to get someone to help you; tighten the adjustable wrench around the bolt for a firm grip.
Make sure the tool fits snugly into the sprocket set, you can easily recognize it by the 12-tooth nut on the cassette itself
Step 7. To loosen the retaining ring, turn the wrench counterclockwise while holding the whip
This nut has a normal thread which must be turned to the left; you may need to exert some force, especially if the cassette has never been taken apart before.
- All this work allows you to extract the fixing ring, a small silver piece that prevents the sprocket set from moving.
- Put it aside in a safe place, you absolutely must not lose it!
Step 8. Remove the cassette after pulling out the ring
The piece is typically composed of some gears, spacers and a series of toothed wheels fixed to each other. Make sure that each element remains in place as you take out the package to have a reference model when you assemble the new cassette. There may also be plastic chain guards between the cassette and the sprockets - you can keep them or throw them away.
- Some gears may come loose on their own, while others may be pinched together.
- In some cases it is necessary to use a thin object to gently pry and detach the sprockets.
Step 9. Clean the hub with an old rag and some cleaner
This area of the bike is rarely washed, so take the time to remove all the dirt; use an old cloth and denatured alcohol, mild dish soap and hot water or an environmentally friendly degreaser.
Part 2 of 2: Replace the Cassette
Step 1. Replace the cassette with a spare that has the same gear ratio
Count the number of teeth on the smaller and larger bezel. Match the two numbers to get the ratio. For example, an 11-32 cassette must be replaced with a spare 11-32; you can find this information printed directly on the sprockets. It may also be useful to know the part number or name. You can take the sprocket set to a bike shop and buy an identical piece.
Step 2. As an alternative, replace the cassette with one that has a different gear ratio
Almost all of these items are interchangeable, as long as they are always of the same brand. For example, Shimano sprockets can be associated with different ring nuts that belong to the same manufacturer; you can even use the old gears with some adjustments. You can buy the sprockets individually or get a complete sprocket set. The cassettes can be disassembled by removing the fixing pins; the latter have the sole purpose of simplifying assembly operations. Overlap the various sprockets to get the ratios of your choice. There are gears with a less common number of teeth than others; keep this detail in mind when you go to the store, because in the end you may find yourself with rings identical to the ones you had before.
- Unless you have a lot of experience, it's not worth using pieces with different ratios. Also, you may have compatibility issues. For example, a SRAM cassette might be compatible with a Shimano hub, but the new SRAM XD series is not compatible with older cassette models. Likewise, Campagnolo hubs are only compatible with cassettes of the same brand. If in doubt, ask your local dealer for advice.
- Remember that when changing the ring nut ratio it may be necessary to change the chain length to accommodate the new sprocket sizes.
- Replace the cassette with one that has the same number of reports. For example, a 10-inch cassette cannot be replaced with a 9-inch or 11-inch replacement.
Step 3. Slide the cassette onto the hub respecting the order in which you bought the various ferrules
Reassemble this element exactly as you removed the old one; you can see a series of serrated grooves on the hub that guide the sprocket set into place. One of these is larger or smaller than the others and on the box you can find an opening of the same size that allows you to align the two components; insert the fixing ring immediately to prevent the various pieces from moving.
It may be necessary to insert a few sprockets at a time; if they are separated, see if there are any spacers (small plastic rings) when purchasing the sprocket set. It is imperative that these elements come mounted in the correct order.
Step 4. Tighten the cassette fixing nut
Use the whip wrench as described above, but this time move it clockwise; gently tighten the bolt with the wrench, but do not overdo it as the thread is very thin and does not require great force. The sprocket set is equipped with a fixing indentation which prevents it from coming out and which emits a characteristic noise when it is removed and replaced.
- Screw in the bolt as far as it will go by hand and then tighten it with the wrench just enough to make sure it doesn't move. As you go, you will hear a distinctive sound reminiscent of popcorn popping. You'll know you've screwed up enough after hearing a couple of pops.
- The sprockets should all move together - there should be no backlash or wobbling of the gears.
Step 5. Insert the quick release rod and mount the wheel on the frame
Once the sprocket set is in place, engage the wheel and chain; now you are ready to resume pedaling.
Always put the chain on the wheel corresponding to the gear that is currently selected on the bicycle; by doing so, you avoid that the chain itself violently clicks on another ring nut as soon as you pedal. If in doubt, select an extreme ratio and hook the chain to the two corresponding gears
Step 6. Change the chain each time you replace the sprocket set
As this element wears, it puts more stress on the cassette. Changing the chain often (every six months or so, if you use the bike regularly) is in fact the best way to avoid replacing the sprockets with excessive frequency. If you fit a new sprocket set, use a new chain, even if you haven't changed the gear ratios.
Advice
- This is a simple procedure that does not require special skills; there are no spring-loaded parts or small ball bearings.
- It is cheaper to buy tools online than in the shop because you don't have to pay intermediaries.
