CS-HG30-8I cassette - what do I need as a replacement? When to replace?

[jase_31]

I have a bike with a 11-32 Cassette, and Shimano Tourney groupset. When replacing the cassette, do I need to keep to the same size (11-32), same make (Shimano) or are they interchangeable (doesnt changing the ratio - affect chain length). Current Cassette is marked CS-HG30-8I. What do I need to get for a replacement?

How do I now when I need to replace? I assume it is when the teeth become rounded, and the chain skips? On a worn cassette and chain, it is better to keep as a pair until the chain breaks - and then replace both?

Photo of cassette attached.

 

[vickster]

You can use a Shimano or SRAM cassette, 8 Speed 11-32 if you’re happy with the gearing, get the same
Eg https://www.wiggle.co.uk/shimano-acera-hg41-8-speed-mtb-cassette/
And chain https://www.wiggle.co.uk/shimano-hg40-6-78-speed-chain/

don’t wait until the chain breaks, replace when worn and the cassette at same time. How many miles has the chain done, in what conditions and what level of maintenance?

 

[Moodyman]

How many miles have you done on the chain? And is it the first chain to come with that bike? Often, most folk can get two chains per cassette and some say three.

As a ballpark figure, one chain will be fine for around 2000 miles depending on terrain and maintenance.

You can check chain wear using the 12 inch ruler method. Look it up and decide if you need replacements.

 

[Asa Post]

How do I now when I need to replace? I assume it is when the teeth become rounded, and the chain skips?

The cassette teeth don't round off when worn, they get sharp. Google for images of "worn cassette" for examples.
The chain *does* skip, but if you measure it regularly (as @Moodyman suggests) you may see that it needs replacing before it gets to the skipping stage.