chainring vs cassette vs chain wear?

8000 miles sounds like a lot, although I know a guy who logs 10k a year and he doesnt replace his whole drivetrain. But he does replace his chain a couple of times a year. Which brings us to the question: are your chainrings still good? if the chain is stretched 1/4"? then I would bet the chainrings are overdue as well. Good pics of worn chainrings can be seen via Google Images... keywords: worn chainrings

all's'miles

curby

Have also found the chainrings don't wear very fast, even though they are aluminum. Believe this is because the high number of teeth share the load. Also, they can be quite worn and not cause any skipping or other problems. But that doesn't mean they should be left on forever, until they look like shark's teeth.

On my bike, I replaced the FSA triple chainrings @ 18K miles. The teeth didn't look bad, but on the middle 39 ring I noticed more "play" than I wanted when pressing on a pedal with the bike static. Also, could see some daylight between the chain and ring when pulling the chain away from the ring at the 3 o'clock position, meaning the chain was tight under load only on the first few teeth on top. Figured that was causing some added drivetrain loss. The replacement rings had an added bonus of making the drivetrain quieter and smoother, like when new.

We all ride in different conditions, but I get ~5K miles on chains (based on the Parktool gauge 0.75% wear), and replace the cassette when replacing the second chain, @ 10K miles. (I tried putting a third replacement chain on the worn cassette the first time and it skipped badly).