At some time in the life of your cycle your going to have to change the cassette, you can take it to the bike shop, but its better you learn you to do it your self
Replacing a cassette is not a difficult job, but there can be a couple of problems you could come up against if you decide to take on the job yourself
Before you start to take off the cassette you had better make sure you have the tools to do it! Two of these tools are very special and your going to have to buy them from a bike shop, as they are not used for anything else.
1. Cassette lock-ring tool
This tool fits into the lock-ring so you can loosen it, there are different lock-rings for Shimano or Campagnolo, but I have found that you can use the same tool for both, as they are so similar.
2. Chain whip
You also need a adjustable spanner, one big enough and long enough to shift a really tight lock-ring, anything over a foot long should do it, but the longer the better also the jaws have to open wide enough for the lock-ring tool, about 16mm.
Lets Get Started
First thing you have to do is to take the rear wheel out, remember to put the gear onto the smallest sprocket, which will make it easier to remove and replace the wheel.
Take the quick release out of the axle, put the lock-ring tool into the lock-ring with the wheel at your feet leaning against your legs and the cassette facing away.
Holding the adjustable spanner in your right hand with lock-ring tool in the jaws of the spanner.
Rap the chain of the chain whip over the top of a sprocket so that you’re holding it in the left hand thus stopping the cassette from turning the same way as the lock-ring.
Pushing down with both hands the lock-ring should come lose, this is where you might come up against a problem, you might need a lot of strength to do this as they can get tight.
When the lock-ring is loose just slide of the old cassette, to fit the new one you just slide it on to the cassette freewheel body, that’s the thing that’s on the side of the wheel hub.
The sprockets will only fit on the cassette freewheel body in one position as there are different sized splines on the inside, then you have to replace the lock-ring tightening with the adjustable spanner.
You don’t need the chain whip as you’ll be tightening the lock-ring against the freewheel. That’s it, just put the wheel back into the bike and away you go, remember to put the chain on the smallest sprocket when you put the wheel back in, it’s a lot easier.