Bicycle Mechanics - Chain lifespan?
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09-04-10, 09:21 AM
I ride a 2ish year old Allez with 500>1000miles and recently my chain/rear gearset has been chattering occasionally and seeking gears now and again, I had tried adjusting it a couple of times to no avail.. Just broke the chain.. it had been seeking badly and jumped then popped..
I assume that repairing it is only a 'get you home' fix and replace it before riding it
09-04-10, 10:34 AM
Wear happens .. lack of lubrication and grit left on the chain hastens wear,
worn chain wears the chainwheels it passes over,
So the whole set may need replacing ..
With only 1000km or so on it, I wouldn't expect a hell of a lot of wear unless it was mostly in bad weather.
And 'chattering' sounds more like indexing gone out of adjustment. Worn chains make a throbby whirr. Measure 24 links and see how close you get to 12"/254mm. If it's less than 1% worn it's still okay.
Chains break for reasons completely unrelated to how they wear. Wear occurs as the pins move in the journals when the chain winds onto and off sprockets. This allows the links to move slightly farther apart changing the pitch by a few thousandths of an inch, and causing the effect called stretch.
Breakage usually occurs from sloppy or aggressive shifting, usually under load, which puts twisting and bending stress on the chain. Eventually some plates get spread to or beyond the ends of the pins, so that when the chain is next under tension a plate falls clear, and the chain snaps. Note that, depending on conditions, lots of time can elapse between what sets up the failure and the actual breakage.
In your case, odds are that your RD went out of trim, possibly from a hanger bending, possibly just a cable adjustment. That caused the auto shifting, which included some under load and eventually the chain breakage.
Replace the chain, and lesson for the future, when the RD starts acting up deal with it before it causes more damage.
And if your chain hasn't had a chance to wear much, your cassette should still be good to go.
Sheldon Brown recommended replacing a chain with only 1/2% elongation, rather than 1%. Another potential culprit is a worn jockey wheel in the rear derailleur.
I'd be a putz not to defer to Sheldon.
09-05-10, 11:34 AM
Chains are so cheap. Just replace them every 2 yrs or 2000km. YMMV of course.
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