Chain skipping - new cassette and chain

Hi all

Just fitted a new chain and cassette to my bike. Chainring is still the original and has covered 4k miles.

The problem I’m having is that the chain skips and jumps on 2 of the middle cassette cogs under anything more than light load.

Now, this is an Aliexpress cassette so there’s a possibility that it’s just poor quality and is destined for the bin, however, considering how well it looks to be machined, and that all the other cassette cos run smoothly, this seems less likely.

Any ideas what my problem could be? I assume that a problem with the chain or chainring would manifest in all gears, not just two.

My original suspicion was that the cassette was somehow assembled incorrectly, since all the cogs except the last 2 are pinned together, but the design of the splined freehub interface should mean this isnt possible unless it’s been machined incorrectly!

Will follow up with photos and videos if necessary.

Cheers

Sticky cables?

The bike has sram etap axs so definitely not cables. Gear selection works fine, I’ve tweeked the indexing, but the problem persists.

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That’s definitely weird then. I’m not fortunate enough to have etap my self but a lot of my friends do and I’ve never seen a problem other than a flat battery. Good luck!

I would not assume it would manifest in all gears. As much as that makes sense, it’s probably not a definite. eTAP will have precise indexing so you know it’s not the derailleur. You didn’t mention what kind of chain it was. Chain and cassette wear are typical causes for skipping so your chain and cassette may not be compatible. If you bought a KO chain to go with that KO cassette, could be the issue. Also, might consider if there is supposed to be a spacer on the inside of the cassette between the casette and the freehub body. It could be everything is shifted slightly inward.

That what would manifest in all gears? The reason I mentioned this is because presumably a faulty chain or chainring would manifest in all gears?

Brand new sram axs flat top chain

There’s no spacer. If this, or indexing, were an issue I would expect problems in more than just 2 gears, as well as problems in the highest and lower gears, which there is not

I assume this has replaced a standard 12 speed AXS cassette?

If so, and you still have the old one, swap it over for a quick spin round the block. If everything works (and the new chain doesn’t slip/fail to engage), you’ve got your answer.

It’s got to be the cassette hasn’t it? Only other explanation I can think of is a bent mech hanger.
Isn’t 12 speed AXS too precise to be subbing in cheap cassettes?

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Does the rear mech kick back before it skips? Had similar when I inadvertently routed the chain the wrong side of one the cage dividers / spacers in the rear mech when refitting.

Chain routing is correct. I triple checked. Note that i only experience these symptoms in 2 gears

Unfortunately i dont expect a brand new chain to work well with a worn cassette

Yes i suspect it has, although i cant for the life of me figure out why. Visually everything looks fine and ive even checked and experiment with the width of the plastic spacers between the cogs.

Apparently a new one doesn’t either.

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Yes, thats sort of the point of this topic. But thanks anyway for your insight

Well here’s the thing: you ask for ask for help, then dismiss everyone’s suggestions (not just mine). It rather begs the question of why you bothered.

Sorry, not sure why youre so bothered by this. I did thank you for your help.

However, I havent dismissed everything. A lot of suggestions are things Ive already tried. Would it make you feel better if I tried everything in this thread again, even though Ive done most of it before posting up asking for help?

I am also using a 11speed casette from aliexpress on my smart trainer and never had any issues with it. I don’t think replacing your chainring will help but if I were you I would reach out to the seller explaining the situation.

Thanks, I’ve done that and just waiting to hear back from them!

May I ask what brand/seller you used? Hoping my issue is just a one off

The name of the brand is Zitto and it has a red color lockring. I don’t really remember the name of the store but a lot of stores sell this cassette. I hope you get a positive response from the seller!

edit: the chain I am using is a KMC-11 speed (purchased from amazon) FYI.

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I’d take it to your LBS and see if they’ve got some cogs / cassette laying around. My money would be on the AliExpress cassette, just out of Occam’s razor. Swap a new cassette on and test; if it fixes it, great, you can buy the new cassette from them. With a brand new chain and (basically) new chainrings, and an Ali cassette, start with the odd one out.

EDIT to add: It’s tough to tell just by looking. The tolerances are so tight… Heck, even shift ramps on chain rings are barely noticable and they make a huge difference. The difference between a brand new and toast chain is a small amount. Even if the machining looks good, it could be off just enough.