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I have been experiencing significant chain skip on gears 11-13 (chain on large front cassette) on a Specialized Allez which is only 4 months old. Regarding specs they are CRANKSET: Shimano Claris R200; REAR DERAILLEUR: Shimano Claris, 8-speed; CASSETTE: SunRace, 8-speed, 11-32t; CHAINRINGS: 50/34T; CHAIN:KMC X8 w/ Missing Link™, 8-speed.

The chain skip occurred even when the bike was new, such that I could only reliably use gears 14-16, since anything lower like 11-13 would skip. The bike had a one-month tune up in November, and still had chain skip thereafter. When the chain is on the smaller sprocket in front, there's no chain skip in gears 1-8, but when the chain is on the larger front sprocket, there's consistent skip on gears 11-13 on the rear cassette.

Fundamentally, I would be interested in the engineering complexities surrounding chain skip and why it occurs. I don't know if it's a problem on entry-level bikes, rear derailleur settings, etc. I

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    Its not a top end bike, but no 4 month old bike should have these kinds of problems, let alone a brand new one, I'd suggest you talk to the bike shop first before getting stuck in. The mechanic can't fix chainskip they don't know about - it would not show up on the workstand.
    – Criggie
    Feb 20, 2022 at 4:08

2 Answers 2

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Disclaimer: My post is based on the assumption of a new rider, or one who is not very familiar with basic bike maintenance. Don't take offense if you found this pedantic.

Tuning the rear derailleur is not a 1-time thing. One should eventually learn how to adjust the rear derailleur, or at least, learn to use the barrel adjuster 'index' it correctly whenever required. Some scenarios where your rear derailleur is off:

  1. Your rear derailleur's cable is new (new bike or just a regularly (say yearly) replacement due to rust or scheduled overhaul)

To fix this: New cable will slacken during first or second ride as it tends to stretch more. You will need to tighten the barrel adjuster. If it skips, it means it's not indexed correctly. Follow this video guide will help you to learn this basic maintenance technique:

  1. The rear derailleur got impacted such as getting a bump from another bike or you laid your bike on the drive side.

To fix this: Check that your hangar is not bent. It should be straight and not curved inwards or outwards. If your hangar is bent, you either have to replace it or go to a local bike shop and get it bent backwards (which may or may not work well).

  1. The shifter is faulty. (Since your bike is new, I really don't think this is the case.)

To fix this: Go to a local bike shop and get it repaired or replaced the shifter.

Other possible causes:

  • Rear derailleur pivot points are stiff due to debris build-up over time. Clean the rear derailleur and lubricate the pivot points.
  • The rear derailleur's spring is no good. It is responsible for accurate indexing. If the spring is old, it might not return to the expected original position. (unlikely, since your bike is new)
  • Cable is not lubricated due to old housing (unlikely for your case)

Is cheap no good? I've built several bikes for myself and friends. The cheapest component I've used it's Tourney (8-speed) and the rear derailleur though cheap, it shifts perfectly. The shifting effectiveness of the rear derailleur it's ultimately based on the accuracy of the tuning. After 2 years, the Tourney rear derailleur on my gf's bike is still running smooth.

My experience of rear derailleur tuning After changing the rear derailleur cable, my tendency is to really overtune (tighten) the barrel adjuster as much as the tolerance allows. It will slacken over time. More often than not, it will take about 2-3 adjustments for the rear derailleur to be in a 'stable' state whenever I put on a new fresh cable. Some folks will overtighten it when putting on a fresh cable, then assess the accuracy later on to make the the necessary adjustments.

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  • Thx - it was based on indexing - that's a great video! A few turns of the barrel adjuster when on the stand and it worked out perfect during a long ride. I already know front derailleur tuning quite well, as that required several rides carrying a screw driver and using small 1/8 turns to tweak.
    – wjktrs
    Feb 20, 2022 at 22:22
  • Glad to know it worked for you! I see you're quite mechanically/technically inclined as well and bet you'll be mostly self-sufficient in bike maintenance in no time.
    – Jeremy S.
    Feb 21, 2022 at 3:41
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Is it really chain skip or a shifting problem?

Usually chain skip happens when you use a new chain on very worn cassettes or chainrings. The chain doesn’t mesh properly with the teeth and jumps over them under load. Another option is insufficient chain tension (on a bike with derailleur this usually means a too long chain).

But since the bike has all-new components this can’t really be the case. Since it doesn’t happen on the small chainring it also can’t be too long chain.

When you are riding it can sometimes be hard to tell shifting problems and chain skip apart.

So first of all: Does shifting work properly with the bike held up and pedaling with your hands? Is there a tendency for the chain to climb up or down to neighboring sprockets? If that’s the case then it could merely be a matter of adjusting cable tension with the barrel adjuster. Check if the rear derailleur is directly under the sprocket. Check if the derailleur cage is perfectly vertical and not angled in any direction (either due to bent derailleur hanger or bent derailleur). Shifting problems in the small sprockets can also be due to excessive cable friction. Check the cable and cable housing. Are there bents or damage anywhere?

Regarding chain lubrication: The outside of the chain should be clean. Excessive chain lube on the outside only attracts dirt. Most of the friction in a chain drive is inside the chain links. Wipe it down.

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