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Chain skipping off front chain rings under pressure

(13 posts)
  • Started 11 years ago by DaveC
  • Latest reply from Charterhall
  • This topic is not resolved

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  1. DaveC
    Member

    Does this indicate excessive chain wear? I've experienced a new chain on an older cassette and found the same thing, chain slipping but on the cassette and not the front chainrings. On the Cotic (~17 months old, with quite a bit of use in winter conditions - also ran dry last week) the chain jumps off causing derailment off the front chain rings, both large and small, when I pedal hard, meaning I have to spin in a lower gear and not apply too great a prssure to pedal.

    Just wondering if I should get a new chain and cassette or a new chain, cassette and perhaps front Chainring (much more expensive).

    Components are Tiagra rear, Shimano chain and cassette (unknown HG model) and Sora Front chaingring crank.

    Cheers,

    Dave C

    Posted 11 years ago #

  2. Charterhall
    Member

    Sounds like excessive wear of not just the chain but also the chainring. Replacing the chain on its own will make it much worse, you'll probably need to replace the whole lot.

    Posted 11 years ago #

  3. Arellcat
    Moderator

    Dave, it's highly likely that you'll need both a new chain and chainring. Your sprockets are steel and may be ok - replace them later if need be. To determine what is "need be":

    Break out your steel ruler and see how 12 full links on your chain measures up. When the 24th pin lines up with the 12 1/16th inch mark, it's time to replace your chain, but your sprockets and chainrings should be fine. When the 24th pin is at the 12 1/8th inch mark, it's really time to replace.

    The Park CC-3 chain measuring device is remarkably simple and effective at telling you, with brutal honesty, when it's time. If you let it go for too long (like, now), it'll bite you when you stand on the pedals at a green light, the chain skips wildly and you accelerate to the ground. That happened to me when cycling up Leith Walk Drive once, and while I lay in a heap trying to extricate myself from my bike, pedestrians carried on ignoring me while motorists drove around me. It also hurt quite a lot!

    Posted 11 years ago #

  4. DaveC
    Member

    Cheers, I have a spare chain in the garage but the last time I replaced only the chain I had the same problem but the skipping was on the rear, cassette, and not the front. I just wondered why the skipping was on the front and not the rear. I could deduce the cassette and chain have worn the same but looking at Sheldon I expect to see light through the teeth between the chain and the ring? Bike is at work and I think I'll order a new cassette (have the spare chain already).

    Thanks,

    Dave C

    Posted 11 years ago #

  5. kaputnik
    Moderator

    Simple way to think of it is that the spacing between the links in the chain and the centres of the teeth on your chainring are now well out of synch with eachother. The chain wants to sit aligned with the teeth, but can't, so every so often one of the pins sits proud of the chainring to allow the next link in the chain to sit in the right place. When you put a lot of torque through it, that pin which was sitting proud suddenly snaps down into the correct place, firing your leg down and forwards as it does so - and often enough to keep you going forwards and into the ground. Keeping torque low enough means that the link (or links) which were sitting proud continue to ride around proud of the chainring.

    Posted 11 years ago #

  6. le_soigneur
    Member

    I had the same issue on my wife's MTB last year.
    The chainring had 2 damaged teeth and lateral flex. But I swappped to a spare, it didn't make any difference.
    I swapped the chain and there was no skipping with either chainring (I sorted out the damaged chain teeth with angle grinder). I bet you it is the chain you need to replace.
    You only really need to replace the chainring when the teeth are hooked - worn to sharp point shapes with undercut.
    The chain, though steel, has 100+ links so each one only needs to wear 5 hundredths of a mm for it to accumulate into 5mm serious chain stretch. The alloy chainring is softer and has no moving elements so it should be good for 1000's of miles on the road.

    Posted 11 years ago #

  7. DaveC
    Member

    New cassette and chain on order. The Cotic X has 11 - 32 cassette so ordered an MTB cassette. I was looking for a reason to change the chainset to a triple as I don't get on with the compact as its either too high or doesn't go high enough. I'll live with it though as at ~£80 for the cheapest triple Tiagra, its a bit too much at the mo.

    Posted 11 years ago #

  8. EddieD
    Member

    I sometimes find it to be a tad frustrating replacing chainrings - not sets, just the rings - at the moment I need 105 compact (50-34) rings for one of machines (I have the chain and cassette) and my usual suppliers (CRC/EBC/Parker/) have one or the other, but not both.

    Posted 11 years ago #

  9. kaputnik
    Moderator

    @EddieD - the Bike Works will order you any possible chainring out of one of their supplier catalogues. There's a baffling array of them out there with the same dimensions and teeth numbers. Most, if not all, offered by Shimano!

    Posted 11 years ago #

  10. thebikechain
    Member

    p.s. if you need any model numbers:
    http://techdocs.shimano.com/techdocs/index.jsp

    Posted 11 years ago #

  11. Coxy
    Member

    I've found it a few times - when you replace a very worn chain, you start to notice how worn the chainring is.

    I always replace an alu chainring with a steel one for mountainbiking. pro a good idea for mucky old commuting too.

    Posted 11 years ago #

  12. EddieD
    Member

    Cheers for that Kaputnik! I was wondering about them - I'll head over and have a chat asap - I work near george square so it's not a long walk. I've decided to delay the rebuild till the weather brightens a tad - the machine is still running fine (with a smidgen more than 1/8th stretch :).

    If my speedo is accurate, the rings have had 13k miles on them, so I think a new set is due.

    Posted 11 years ago #

  13. Charterhall
    Member

    @EddieD you may be able to save yourself a few pounds by buying Stronglight chainrings to replace Shimano. Available from Spa Cycles http://www.spacycles.co.uk/products.php?plid=m2b2s149p0&tbv=STRONGLIGHT_PARTS_&_ACCESSORIES_Components_-_Gears_-_Chainrings_-_Stronglight

    Posted 11 years ago #

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