Just built up bike

105 rear derailleur with a sram force crank, Running 9 speed and A single 39t ring in front right now as I dont have a front derailleur and was hoping to keep it 1x9

I used an old chain which I think might be my problem, but in my stand everything was smooth. Shifting was crisp, nothing seemed to be out of place

Im thinking I either need a new chainring or chain, my cassette should be fine, and I thought the chainring was fine because the teeth looked good but I could be wrong. They are not visibly worn down much.


I rode it to work this morning and everytime I came out of a stop the chain would click/clunk... and seem to fall off near the front of the ring. Really bad in traffic...

I have a chain guard on it right now which is keeping me from completely loosing the chain

But my knee is in great pain from all the chain dropping.

anyways any insight. Thx!

I would assume this is an issue with your chain line. Can you tell if the teeth on your chainring are hitting the inside or outside plates on the chain?

Are you using a single speed chainring with even teeth?

thats what I was thinking, but i switched the ring from the outer to inner part of the crank and still had the dropping. adjusting derailleur accordingly i believe.

Is it possible for you to ride on a quiet street or large empty lot so you can look down at the chain/cassette/rings while starting up (and not hit a car)? Can another ride next to you and watch your drivetrain? What rear cog are you in when the chain drops off the ring? One issue is that thr ring is designed to allow the chain to drop off, that's called shifting when there's a second ring and a der. So the tooth shape doesn't grab the chain as well as a dedicated single ring one would. It's possible that the ring's teeth and chain are so worn that they don't fully mesh and when under power the chain tries to climb up and over the teeth. but this usually doesn't result in a drop. Andy.

chainring was in backwards, facepalm... thanks for help though.