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My bike's a 24-gear trail/road hybrid, and I've had it for about three years (although I've been riding it much more lately than in previous years).

For a long while, I've had an issue with chain skip happening seemingly at random, even on level, paved paths, however this issue was always more serious going uphill. I decided to replace my chain yesterday (it's appropriately sized, was pre-lubed, and none of the links locked upon inspection), however on this morning's commute I still got the same amount of skip, likewise more serious going uphill.

I've tried using best practices to avoid this issue, as well:

  • I avoid pedalling while changing gears

  • I've checked my front and rear derailleur alignment (and adjusted it as best I could, there's still a very, very slight amount of scraping on the front derailleur if the chain has to travel too far laterally e.g. between my largest front sprocket and the smallest sprocket on the cassette on the rear wheel)

  • I've double-checked that the links don't block, multiple times

  • The teeth on the front sprockets as well as on the cassette don't seem to be overly worn down

Two more factors could be relevant to this; this new chain has those "tool-free" break links (you bend the chain to attach or detach one side of the link and break the chain), and I'm a more heavyset guy, so I pedal hard - I think this could be putting more stress on the chain.

I'm not sure what else I can do to reduce chain skip.

Update: I've gone by my LBS and apparently one of the chain gears is in fact worn down (I just didn't know how to tell, apparently).

  • How many miles on this bike? My rough rule of thumb is a chain lasts 2000 miles, a rear cluster 5000, and the most-used front ring 15,000. But running a worn-out chain will damage both front and rear sprockets sooner. – Daniel R Hicks Jul 10 '15 at 16:54
  • I wouldn't say much over 1200 miles, but probably half of that was done over the last month. Could this kind of usage contribute to sprocket wear? Also worth mentioning, the old chain was most definitely worn. Well over 1/8" lengthening, and I'd neglected to lube it regularly. – Jules Jul 10 '15 at 16:59
  • Yeah, my 2000 mile rule assumes reasonably regular lubrication. If the chain were run dry that would contribute to wear of both the chain and the sprockets. – Daniel R Hicks Jul 10 '15 at 17:02
  • Alright, I'll compare the sprockets to some pictures from online to check - again - that they are or aren't worn, in a few hours. – Jules Jul 10 '15 at 17:22
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Your cassette and possibly chainwheels are worn out. When a chain wears, the cogs wear down together with it and will not mesh correctly with a new chain.

Worn cogs do not look like the teeth would be actually wearing down. Instead, the teeth get narrower and eventually develop an asymmetric "shark fin" shape. If you do not know exactly what to look for, a worn out cassette looks like new.

  • "the teeth get narrower and eventually develop an asymmetric "shark fin" shape" that's what I was looking for, and what I meant by "wear." I didn't notice any such deformation. – Jules Jul 10 '15 at 15:22
  • I find that while my front chain ring will tend to sharkfin with wear, my rear cassette does not. Instead I just end up with increasingly wide valleys between the teeth as they wear. – MPoirier Jul 10 '15 at 16:07
  • A new sprocket has teeth separated by "valleys" that are exactly circular. As the sprocket wears, the "valleys" become more oval. – Daniel R Hicks Jul 10 '15 at 19:21
  • It's harder to say with cassette because the teeth are slightly irregular as new. Like @MPoirier and Daniel said, it's easier to see from the "valleys". I get shark fin effect in some but not all cassette teeth, in fixed gear cog it's easier to see. – ojs Jul 10 '15 at 20:32
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  • Pedaling while changing gears in important to avoid damage to derailleur and chain. Gear shifting proper technique by Sheldon Brown.
  • Shift the gears so that chain is on the middle chain ring(at the pedals) and approximately on the middle gear on the cassette. Verify that the derailer with the chain is vertical, if not adjust accordingly.
  • Also, it is possible that chain may be skipping if the derailleur is slightly bent - in this case bring your bike in to a reputed local bike shop(LBS) and have it checked out. It may save your derailleur from further damage and possible need to replace it.
  • Changing to an easier gear just before you climb and spinning pedals (lower effort but slightly higher pedal cadence), instead of mashing on a tougher gear (applying greater force and lower pedal cadence) helps avoid chain skipping.
  • Thanks for the Sheldon Brown link, I'll check it out. I'll also do the check you mention in your second point and stop by a LBS all else failing. – Jules Jul 10 '15 at 15:23
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It turns out that the issue was caused by a worn shifter cable casing -- the plastic tubing.

LBS replaced it at around a fifth of the price of replacing the cassette and/or chain gears, and everything works like a charm now.

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