Originally Posted by
Witterings
How do you know when you chain and cassette need replacing, I bought my bike 2nd hand and have done 1600 miles on it since, I was having some issues with the rear shifting into lower gears and have swapped the cable and re-indexed which has smoothed it out considerably but occasionally it doesn't jump up and I think it's always between the same 2 gears.
Sounds like the chain is overdue and probably worn down the cassette You can look at the teeth on the gears you're having problems with and probably see they're worn differently.
Best to replace the chain and the cassette at this point--if you just replace the chain, you'll probably find the skipping becomes even worse.
From here on in, use the chain checker I linked above to detect when it's time to change the chain before it wears down the cassette again. People vary in how many miles they can get out of a chain because of differences in riding conditions and style, so there's no general rule.