I actually had to replace the rear cassette cogs. It was time, and a good idea since the chain was replaced about 200 miles ago, and you should also replace the rear cogs at the same time.

Evidently, when these wear out, the shifting gets sloppy, and it can slip. This can suck if you are standing up while climbing a hill. It can hurt your joints if it shifts when you aren't expecting it, and I have bad ankles, so therefore I replaced the parts.

I have never owned a bike that had to have anything replaced due to use, and MUCH less one that had gear needing replacement before a season was over with.

Pretty crazy stuff man.