Do freewheel/cassette/chains come as a set?
Your easiest solution is to simply buy another of exactly what you have


8 speed cassette, 11-28 teeth
8 speed chain.


They don't come as a set - you need to buy one of each.  Its up to you if you want to get cheaper or more expensive parts.  The lifespan and weight is what varies with price.

Depending on wear, your front chainrings might be getting tired.  But I've seen some severely worn ones still working fine.

Any 8 speed chain will be fine - you could even mix and match KMC chain with a Shimano cassette.   But you need 8 speed chain (possibly labelled as 6/7/8 speed) and you need an 8 speed cassette.

If you want to get a bit more adventurous you could look at a 30 or 32 tooth big cog.  This would give you a lower-low gear for hillclimbing.  Its totally up to you whether this is required.

Downside of enlarging the cassette is that your rear derailleur might not fit, or it might chatter on the lowest gear.

Chains come in lengths longer than what you need.  114 or 116 links (or half-links)   So you shorten them to the same number of links as your old chain.

You'll need tools to do this - there are some special bike tools.


Cassette lockring remover (Undoes the lockring retaining the cassette on the freehub)
Chain whip (to hold the cassette and therefore the freehub still while using the lockring remover)
Chain tool (to shorten and fit the new chain you need a chain tool.  Chain will probably come with a one-time use pin, or you can fit a master link to make life easier next time.)


Also need rags and cleaners etc, and possibly chain lubricant.