One of the teeth on the cog that I use the most has worn down after only 2000 miles, causing chain skip. And that cogset replaced one that lasted only five months, and an even shorter distance.

Doesn't that sound like abnormally fast wear? I do use the cog in question to climb virtually every time I work out, putting heavy load on that cog for about a third of the 2,000 miles. But even so, the wear sounds abnormally fast to me. What am I doing wrong? I don't lubricate my chain, and I wonder if that is contributing to the rapid wear.

Richardpu-

I think you could have a stretched (worn) chain, and prematurely worn for lack of lubrication.

read https://sheldonbrown/chains.html

but as well that does seem to be alot of use of that one gear, but I'm not the authority on that issue. Sheldon has alot of very good information on his website

Peter

I'm still wondering if this is a troll or not: given the continuous and omnipresent religious wars surrounding the issue of chain cleaning and lubrication, and the bottles of chain lubes always displayed very visibly in most bike stores, I can't believe this question isn't some kind of joke.

But okay, I'll bite: if you get 2000 miles on a dry chain, I say you're getting a really good mileage
Try cleaning then re-lubing your chain regularly. During the dry season, once every 400 miles should do, a lot more in winter. The reason why you need to lube a chain is because the rollers wear much faster if you don't (metal rubbing against metal), the chain stretches, and eventually damages your cogs and/or chainwheels. The reason why you need to clean and re-lube the chain regularly is because the oil in the chain eventually gets contaminated with road grit, which then acts as a grinding paste.

There are numerous posts on how to clean a chain. The bottom line is that you need to get all the contaminated oil out of the rollers somehow, usually with a solvent of some kind. Some swear by this-or-that solvent, some swear by ultrasound cleaning, some swear by cleaning the chain on the bike, some off the bike, some swear by cleaning the chain when the moon is full, etc... Search on this here forum and you'll get a million answers. Also, get a chain stretch checker and remove the guesswork out of deciding when to change a chain so as to not damage your cogs/rings.

What is a troll?

Funny, we never had any problems with the XTR cassette on our tandem. And I'm about 125% of your average rider when it comes to size and torque potential.

https://en.wikipedia.org/wiki/Internet_troll

You mention that the cog in question is under heavy load. Are you shifting under heavy load with this cog? That can be the cause for rapid wear. And if it is with a bad chain line (big chain ring/big cog or small chain ring/small cog) things are even worse.

Did you change the chain when you changed the cassette? 2000 miles is way too soon for any significant wear unless a badly "stretched" chain was used.

He never bothered to lube the chain.

Also, he doesn't say what kind of riding he does. If he goes ride hard in crud with a mountain bike and never cleans the chain, it'll be busted in less than 300 miles

Preach it brother....