Looking for a little lower gearing on my gravel bike, I replaced the crankset with a FSA Omega with 46/30 chainrings, along with a new bottom bracket & chain.

If I stand on the pedals while on the small chainring, I can get the chain to slip & pop off the chainring. This makes starting and climbing pretty rough ;)

The front derailleur looks to be adjusted correctly.

I'm looking for other ideas of what could be causing the chain to pop off, or maybe the FSA Omega crankset is just incompatible with my bike?

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    Did you replace the chain? – paparazzo Dec 22 '17 at 19:25
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    chain, chainrings/crankset, & bottom bracket all replaced. – mike Dec 22 '17 at 19:31
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    Check tension (chain length) – paparazzo Dec 22 '17 at 19:41
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    @Criggie -- clearance seems good, but could be an issue. I was running 48/34 chainrings previously (14 tooth difference) – mike Dec 23 '17 at 1:55
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    Chain angle seems like the most likely problem, though it's also possible that the small ring is simply improperly installed. – Daniel R Hicks Dec 23 '17 at 2:57

Assuming you have a 10sp RD 350 SS short cage (R350 GS seems to be a 9 speed item), you have possibly exceeded the total capacity and are not getting enough chain tension.

Capacity with 48/34 rings was 48 + 36 - 34 - 11 = 39. Capacity with 46/30 rings is increased to 46 + 36 - 30 - 11 = 41. AFAIK, only long cage derailleurs for triple rings have that much capacity.

Do you really need a 30t small ring? Would increasing it to 32t - to decrease the total capacity - be ok for you? Alternatively you could think about replacing the derailleur.

  • I suspect you may be correct. The Shimano RD-350 has a spec'd capacity of 37, and was probably squeaking by with 39, but 41 is probably too far off. – mike Dec 26 '17 at 6:49

Stupid mistake, here's hoping others will learn from my error!

When installing the 30T chainring on the FSA Omega crankset, there wasn't an obvious orientation. It looks like I installed it the wrong way.

I re-installed it flipped the other way, and everything seems to be working. Three test rides and no chain drops!

  • Excellent spotting - thank you for coming back for closure. Do please mark this answer as Accepted by clicking the checkbox/tickbox to the left. – Criggie Jan 4 '18 at 1:44

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