New cassette + new chain but....

[Manonabike]

I have a little problem with my bike after a new cassette and new chain. Sometimes, when I go over a stone or similar thing the chain jumps off gear completely and I have to shift up or down before it goes in gear again. I have changed cassettes and chains many many times but I never encounter this problem before.
I have been trying to remember the steps I took to cut the chain to length and I might have measured against the old chain and if that is the case then I cut it one length too short by not taking into account chain expansion on the old chain. Could that be the problem? I will try to measure the chain again tomorrow though.

Any suggestions?

Thanks in advance

 

[Cubist]

No, measured against your old chain the new chain if anything may be one link too long. If you are using a powerlink to join the chain that will add another extra link. Add a sloppy derailleur spring into the mix and that could well be your problem. Measure again using the "large cog to large cog and add a link" method is more reliable.

 

[Manonabike]

Thanks for that.

Today I measured the chain and it appears that you were right, one link too long.

I'm yet to go out and test it but I'm confident that was the problem.

Cheers