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I recently converted my bike with 9 speed 105 from a triple to a double chainring. I installed my new 34/50 crankset and noticed that chain would slip across the teeth of the 34t chainring whenever under serious load. It's completely fine on the 50t ring, no skipping whatsoever.

I've been looking around for answers and the most common explanation/answer I find is that the chainring and/or chain is worn out and needs to be replaced. The thing is, the chainring and chain are new and showing no signs of wear. I though it might be slack in the chain, but I remeasured it and it is the correct length.

Is it possible that my 9-speed chain just isn't compatible with this particular 34t ring?

Any help would be great, I'm pretty stumped.

BTW this is the new crankset I swapped. https://www.aliexpress.com/item/3256802561706591.html?spm=a2g0o.order_list.0.0.21ef1802Xiq4n2

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  • Is the chain badly worn?
    – Daniel R Hicks
    Jul 19, 2022 at 16:17
  • Did keep the previous derailleur? Possible that the different cage design causes interferences.
    – Renaud
    Jul 19, 2022 at 16:38
  • If both chain rings came with the crank set and they're not worn out, then if the chain works well on one chain ring, it should also work well on the other chain ring. You can check the condition of the chain with a chain tool, and what nightrider says, the chain may be too long for your smaller chain ring.
    – Christine
    Jul 19, 2022 at 18:20
  • The chain has no stretch and less than 100 miles on it.
    – pazzmaul
    Jul 20, 2022 at 17:11
  • I'm also using the original 9s 105 derailleur, but I don't understand how that could effect the front chainring.
    – pazzmaul
    Jul 20, 2022 at 17:13

4 Answers 4

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Smaller front chainring leaves more free chain so check if the derailleur tension spring is still active and not completely out of range. This would manifest the most obviously with the smallest sprocket.

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So, I was running out of ideas and though maybe the sprocket just wasn't compatible with my 9 speed chain. I swapped it for an old 11 speed at the same length and it fixed the problem! Really weird.

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Your new chain is probably skipping because this crankset is garbage.

Based on some of the review photos, I'd drop the crankset like it is on fire.

enter image description here

Avoid out-of-the-saddle efforts, stay seated, studiously check all sides of the cranks for cracks every month, and keep your helmet on.

Not worth the savings IMO.

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    I missed those reports/images in my abbreviated research into the product. Wow! You are right to give that warning in your answer. A catastrophic failure like that is going to injure or even kill somebody as it occurs when the rider is fully committed and completely relying/dependent on their equipment not failing.
    – Ted Hohl
    Aug 31, 2022 at 14:02
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I followed the link provided for the crankset/chainring in the question, and looked at the reviews. There was one person who described the same condition that you experienced with your crankset:

"Small chainring skipping when applying high torque (eq. climbing) 22 Mar 2022"

A couple things come to mind.

It could be a quality control issue that let some 34 tooth chainrings through that would not perform well. Your crankset does not seem to alone with the problem. I have personally seen this with a new off-brand cassette myself, so it may not be common, but it is not impossible.

It could also be that with your crankset, the spacing between the two chainrings may be tight enough that a wider 9-speed chain would not bed itself into the chainring teeth correctly due to some interference from the larger chainring or something else, whereas the narrower 11-speed chain did not have this interference. I have run a 9-speed chain on a modern-Shimano 11-speed crankset (Ultegra 6800) without issue, so I know some configurations can work.

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