Chain keeps coming off

[BrumJim]

Chain too long?

Is the freehub running smoothly? If this is sticking, every time you freewheel, the chain will keep moving and then come off the chain ring.

Chain length is fine (I didn't fit it, done professionally). Free hub runs really sweetly.

 

[geocycle]

Have you checked the derailleur alignment? I just remembered I once discovered the rear derailleur had been bashed when the chain fell off the front.

 

[T4tomo]

Riding over rough ground.

Then a clutched / shadow RD is what you need. basically the bouncing on rough tracks is more than a regular RD can cope with, the arm bounces forward, you get chain slap on the stay and on the small ring with inherently less tension the chain just bounces off.

 

[figbat]

Then a clutched / shadow RD is what you need. basically the bouncing on rough tracks is more than a regular RD can cope with, the arm bounces forward, you get chain slap on the stay and on the small ring with inherently less tension the chain just bounces off.

It certainly will help, but clutched RDs were really invented for 1x systems with long caged RDs. A firmly-sprung regular RD should be enough for a 2x system.

 

[BrumJim]

Is this what you've done or a suggested failure mechanism? If the RD is not tensioning the chain well then this could easily cause the chain drops.

Under what circumstances is the chain dropping? Riding over rough ground? Changing gear? Back-pedalling?

Point to @figbat . Bike shop reckons it is this.