Assessing chain wear and cog damage

Also check your big ring. Look for a "shark's fin" appearance of the teeth as opposed to an even left to right alignment. This is one of the results of a chain stretching.

soloist said:

My current chain has been in use for 6,000+ miles. It's started jumping to a lower cog on the cassette during hard climbs. It's probably stretched and may have damaged the teeth on the most often used cog, hence the unexpected shift.
I have two questions about putting things right.
1. I'm considering buying the Park chain checker to keep this from happening again with a new chain. Is it foolproof in detecting chain wear? That's important given my fool factor.
2. Is there a reliable way to decide if the cog (or whole cassette) should be replaced? Eyeing the teeth won't cut it...keep that fool factor in mind. It's an XT, if that's a consideration.
Thanks.

1. Yes, the Park CC gauge is fool proof, as long as you remember to check the chain every month or so. As long as the 0.75% side of the gauge won't fall into the chain, you're good to keep riding.

2. If the cogs or chainrings are worn, the new chain won't fit them. You'll be able to see the first few links of the chain engage the teeth, while the rest of them won't seat, even when you try to pull the chain tight.

If in doubt, you could take the bike to your LBS for a check.