Originally Posted by
Dan Burkhart
The most reliable way to diagnose a worn cassette is to install a new chain and look for the symptoms as described in the OP. It has to be pretty far gone to be obvious visually in my experience.
Couldn't agree more. It's quite difficult to visually diagnose a worn cassette. What you usually find is that the chain will skip in the middle of the cassette on the gears that see the most use but, will still shift ok in the upper and lower gears.