Originally Posted by
datlas
Does not sound right. Make sure you have a good set of calipers to measure. If it's new a chain should last at least a few thousand Km.
You probably do NOT need to change your cassette unless it's really worn, most cassettes will last 3-4 chains. Going from 11-25 to 12-25 should not be a problem if you choose to get a new one.
Yes, all true. But if the chain IS that worn, it has likely ruined the cassette. Best to change both. So time for some questions. Was the chain well lubed? Was it clean or fouled with grit? Did you always ride cross-chained. I'm just looking for any reasonable explanation for the rapid wear.