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1. The wider your range of gearing on your cassette, as in a 11/30 like yours, you will more likely end up running on a couple of cogs most of the time, if your commute is mostly flat. This causes those 2 or 3 cogs to wear quickly, which in turn causes your chain to wear quickly. This gets mentioned very little on these forums but I can attest to it. (this phenomena can be regulated by changing front rings or shifting habits)
2. The dirtier the surface you ride on the faster your chain will wear. Debris is kicked up from the front tire and onto the chain. The more debris on the road, the more lands on your chain. So therefore bikes ridden on unpaved or extremely dirty roads, wear chains out faster. Conversely, road bike chains often last a long time. I can attest to that as well.
3. Changing a chain to spare a cassette is always suggested on here. But in fact it often doesn't work out that way. See #1 and #2 to see why. If your chain wears out every 1000 miles as mine and yours do, then you can see that you will quickly be needing new cassettes if you didn't catch the chain in time. Often if the checker gets to the .075 mark then it is too late. Often that happens in under 7000 miles for me. If you run a $20 chain and a $20 cassette then why not just run them 2000 miles and replace them at the same time? That is pretty much what i do any more. Obviously if you have a $100 cassette then your methods will change.
Lastly, a lot of people will come on here and tell you that you are not maintaining your chain correctly. This is bunk. I have tried it all and if you ride a bike and use a limited number of the cogs frequently, on dirty roads, your chain will wear quickly. It can, does and will happen, often in less than 1000 miles.[/QUOTE]
Good points- The chain is only skipping on one or two of the cogs I tend to camp out on. I've been running XT cassettes because they're nice and light, but I think I'll go with something cheaper. At least in the winter. The bike has full fenders, rack, and panniers full of clothes and groceries so weight is sort of a moot point anyway.
So- can anyone recommend a good cheap 8 speed cassette or place to obtain individual cogs? Its always the smaller individual cogs that go first.