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I was replacing a worn-out 34-teeth chainring on my MTB crankset. In the course of the work, I detached the granny gear chainring (22-teeth).

Compared to the big chainring, which has all these ramps and non-regular teeth shapes designed to facilitate gear change, the small ring is completely flat. It looked completely symmetric to me, apart from apparent slight wear on one side of teeth caused by chain contact.

After I'd given it some thought, I flipped the granny chainring over so that another side of teeth was used to contact the chain. This is a regular practice with single-speed chainrings which are symmetric, and it is used to double their useful life span.

However, after I'd put everything else together and adjusted it, I took it for a test ride. Immediately I uncovered that shifting up from granny gear to big gear was now accompanied with chainsuck, as the chain managed to "stick" to the small ring all the way around its circumference. It happened in about nine of ten shift attempts.

No amount of tuning of the front derailleur helped to solve this problem. Now I start thinking whether my judgement about the granny chainring was wrong, and it is asymmetric and cannot be flipped over.

Another possibility for chain suck that I can imagine is that the new big chainring is actually smaller — it has 32 teeth. It is also possible that I installed that new ring incorrectly (should have rotated it 90 degrees relative to bolt holes); but then again, I cannot see how it matters as the smallest ring has no ramps which could be aligned against the big ring.

So what should I do? Flip the granny gear back, look for a bigger chainring, or rotate it?

The crankset is Truvativ X5, 22/34t. The derailleur is SRAM X5.

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    It could also be assymetric in terms of a slight offset between the plane in which the teeth lie and the plane in which the fixing centres lie. I've seen this on cheap triples. You'd probably havew noticed that of course
    – Chris H
    Jun 8, 2018 at 8:09
  • If the new chainring is smaller than the one you replaced it with, you will want to move the front derailleur down the seatpost a bit — ideally, you want the cage of the derailleur to go as close to the chainring as possible without actually making contact with it. Also, if the chainrings are showing visible wear, you may want to replace the chain before trying any funny stuff to eke squeeze a little more life out of your chainrings.
    – Ryan Lue
    Jun 8, 2018 at 8:56
  • @RyanLue Yes, I tried moving the derailleur down and even up. The old chain was thrown away together with the old big chainring, as its wear (elongation) was 0.75% or more.
    – Grigory Rechistov
    Jun 8, 2018 at 9:36
  • What crank/rings do you have?
    – Argenti Apparatus
    Jun 8, 2018 at 15:55

1 Answer 1

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I think @Chris H is most likely correct, the ring is probably not symmetrical.

Other possibilities are that you did not install it quite correctly, or that there are raised burrs caused bu wear that are hanging on to the chain.

If you really want to find out if you can reverse the ring, install it the 'correct' way around, get shifting working, then reverse it again. That way you know that shifting setup is not causing the problem.

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    After a very careful second look at the granny gear chainring, I noticed that it indeed is asymmetric in regard to flipping — all teeth are a bit curved to one side. This evening I flipped the ring back to its original position, and this time I managed to tune the derailleur to behave properly. Apparently the curvature of teeth is enough to keep the chain longer during shifts and to cause chainsuck.
    – Grigory Rechistov
    Jun 8, 2018 at 19:24

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