Chain dropping from big ring

Hi There, this is new to me. I have a SuperSix w 11spd eTap, bought it new in 2018. The cranks are the si Cannondale and shifting works fine. However it’s common that the when in the big ring, say, a 52x21 or 52x19, when i shift to a smaller cog (sometimes) the chain simply comes off the big ring, but it drops to the little ring, not out of it. Shifting itself never causes problems from ring to ring (people complain about sram but i don’t see the issue). Are my chainrings worn? This bike has had 4 different chains and about 25,000kms. The rings on the si cranks are FSA, and am looking at Praxis as replacement. The bike has recently been tuned at its respective retailer, with good mechanics. Help!

Take it back to that retailer and tell them they aren’t finished with the previous work. Even if stuff is worn to the point of needing to be replaced, they should notice that.

My money is just on an improperly tuned derailleur.

edit: Adding to the first paragraph: if they come back and tell you it’s worn and needs replaced, I’d take it to a different shop if possible. Chainrings that worn should have been noticed during a tune in my opinion.


I had a similar issue with my Shimano drive train and it ended up being a worn chainring.

1 Like

UPDATE: don’t mix KMC chain with a sram drivetrain. it shifts fine, it’s slightly noisier and won’t last longer. but your front shifting may suffer. I had the perfect storm of a worn chain and a (very) worn 52 ring. Got new chain last week, then the praxis rings arrived. Result? quiet bike. easy shifts. no dropped chain. thanks for all who chimed in.

1 Like

Pix of said chainring?

Praxis Buzz.

I was wondering if you had a photo so I could see what very worn is for curiosity

oh I see. I threw it in the trash, man. A very worn out chainring will have its teeth filed into thin nubs, no wonder the chain dropped when slightly cross-chained (e.g. 52x19 and 52x21 on a 11-26 cassette). Plus it was KMC and had a bit over 0.5% elongation. It’s my 4th chain on this cassette, and miraculously there was no skipping when installing a new chain (I get an average of 5,000kms till 0.5% stretch). The tricky part is that the wear out process is gradual and organic; you don’t quite notice till havoc sets in. It’s easy to measure a chain wear (chain wear tools), but eyeballing a worn out chainring offers more of a challenge. I’m sure you can find pics on google of trashed chainrings - sorry i can’t be of further help.