I’m trying to turn right. I’m waiting for a gap in the traffic. Suddenly, I spot it. I push my foot down on the pedal expecting a smooth forward motion. Instead, I hear a horrible grinding sound. My foot slides further than I expected and the bike cowardly inches forward. I spot the gap in traffic narrowing and rushed I try to pedal again.
I must be one of thousands of London cyclists who’ve experienced this. How do I know it? Because I hear the grinding sound all the time. At traffic lights especially.
But why? Why is your beautiful bike causing you so much hassle at this moment of need and potentially putting you in a dangerous situation?
The answer probably lies in the cassette.
The cassette is a true thing of beauty. A complex marvel representing the progress of bicycles. But when it is worn out it’s a true pain the %*$£”!
When you apply pressure to the pedals the chain tries to grip the teeth. If the teeth are too worn then the chain will simply slide forward.
Before definitely pointing the finger of blame on the cassette it is worth noting that there are other potential culprits. One is the chain. Two is the rear derailleur indexing.
With some Poirot style investigating you should be able to find whodunit. The first thing to do is to check if the chain is worn.
If the chain seems worn then maybe it is a good time to replace it. It is also worth checking the teeth on the cassette. The one in the picture above is worn out where as the below is a new cassette. You can see a new cassette has more clearly defined teeth.
Replacing the cassette
If this is your culprit then replacement is fairly easy. For the bike shop route you’ll be looking at £25 for labour plus the cost of parts. For a Shimano cassette the cost can be as little as £23.99. But the prices go up from there.
You could also choose to do it yourself. The only bad news about this is that you do need some bike specific tools. Namely a chain whip and a lockring tool. This will set you back £10 – £20. You’ll also need a spanner or a wrench.
Doing it yourself will work out cheaper even with purchasing the tools.
I put together this below video while I was doing the cassette replacement on my bike. Note that it is common practise to replace the chain at the same time as installing a new cassette (unless the chain is only a few weeks old anyway).
Also in the overhauling your bike series:
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As seen on The Guardian, BBC and The Independent.