skiingfury

Are chainrings different? I went through three chains in 500 miles last year on my MTB until I replaced my middle chainring. No more issues. I can't imagine that cassettes would behave any differently.

HerrKaLeun

The load on a (much larger than cassette sprocket) chainring is spread over more teeth. For the cassette it is also the smaller sprockets that skip first.

But yes, if the chain ring is so worn out it can wear the chain as well. I don't know if a chain ring survives 5 cassettes on average, but i assume you wear out many cassettes before you wear a chainring. also depends on the quality of the chainring. I often see bikes with brand name RD and cassette, but no-name crank. People that ride a lot may be able to provide some evidence.

Bike Gremlin

Not disputing, what you say makes sense, just asking: if a worn cassette doesn't wear the chain quickly, how come a new chains stop skipping on a worn cassette rather quickly, unless it too becomes worn ("stretched")?

DaveSSS 

Worn cogs or chain rings will not cause premature chain wear. The teeth change shape but not pitch.

If chain rings become worn you suffer chain suck. If cogs become worn, then a NEW chain will skip on the most-worn cogs.

As I also noted previously, a chain with only a small amount of use on it will not skip on a cog, where a new chain will. A new chain will start to wear immediately after you begin to use it, but if you check the chain over a 12" or longer length, it will show no measureable elongation, even though it no longer skips on a worn cog. If you don't believe that, use a chain for 2-300 miles on a new cassette, then put it back on a worn cassette. It should no longer skip.

Different brands of chains wear differently. I've used Campy Chains for 6,000 miles and measured far less than .5% elongation, using a full length measuring gage. Chains with that much use will be totally shot due to excessive roller and side wear on the plates. Elongation is not always the area of greatest wear.

Here's an excerpt from Jobst Brandt on chain skip.

" Skipping Chain

That a new chain does not want to engage used sprockets may be
obvious, but in theory a new chain cannot freely engage a new rear
sprocket under load even though it has the same pitch as the chain.
That is because the tooth being engaged would be under load and this
is a contradiction in itself. Therefore, a slightly worn sprocket,
that has pockets in its load bearing face is even more reticent to
engage a new chain with perfect 1/2 " pitch.

Sprockets, by the way, do not change pitch when they wear, only the
tooth form changes because the number of teeth remains the same and
the base circle remains essentially unchanged for normal sprocket
wear. On fixed gear bicycles that are ridden until the chain is 5%
out of pitch, the base circle may be slightly reduced but this only
makes the fit of a new chain worse."