If you have a ruler to hand, measure the pins on the chain. They should measure exactly 12 inches pin to pin. If much more than 1/8th out then the chain is worn. It's common in that case for the cassette to be worn too. That's most noticeable if you put a new chain on and it slips as you ride.
Typically, we like to think a chain is good for 2500 - 3000 miles before it needs changing and you'll probably go through 2 or 3 chains before the cassette needs changing.
Thanks for that, every so often, for no rhyme or reason I get a clunk/click form what sounds like the bottom bracket, sometimes it feels as if the pedal jumps round.
I thought it might be the bottom bracket bearing, so had a new one fitted, but its still the same.
It might be the chain and rear cassette........
Thanks.
