As per the title, took my full sus bike out at the weekend and the chain was consistently coming off, to the point where it was extremely annoying. I didn’t have time to give it a thorough going over as I got back quite late but I was wondering what could be the main causes?

It’s a 2×10 setup with bash ring (old fashioned I know but it usually works fine)
Both chainrings not excessively worn, seems to happen more on 39t one though.
Clutch rear mech and chain retention device (bionicon) fitted underneath chainstay.
Chain not excessively worn either, nor is the cassette as both have been replaced in the last year and checked for wear since.

I know going 1×10/11 and narrow/wide would solve it but I’d rather not go there if I don’t have to. Plus the 2×10 works (normally).

Scratching my head a bit here so appreciate any help.

Clutch slack? Chain device moved? Cable tension in front mech? Chain more worn than you thought?

Chain too long (slack), front mech too high, where’s it coming off top or bottom?

Not dropped a chain despite not using a clutch mech, running 2X with Gamut bash and chain device.

I’m guessing the chain is too long.

Thanks for the helpful suggestions. Checked it over and the chain is the right length, clutch mech still feels nice and strong (compared it with my XT one on another bike) so I’m guessing it’s something to do with the chain device. Although that moves freely and seems ok.

I sense a tedious process of trial and error coming up…

Derailing at the front will obviously start at the top where the chain fails to engage properly with the teeth. Is it a cut down triple or a proper 2 by 10 ? The chain shouldn’t derail even with the clutch disengaged. Does it always come off in the same place, IE could your front mech need adjusting ?

Wonky chainring
Damaged or bent teeth (not been brushing) 😆
Bent chain
Poor chain-line

Have you checked the freewheel is working correctly?

I went with a mate to Sherwood ages ago & the chain on his bike (I borrowed a FS bike from a friend for him) kept coming off.
It turned out to be the stupid plastic chain catcher behind the cassette was loose, kept catching the cassette causing it to rotate slightly when freewheeling which was slackening the chain along the top run (between top of cassette & chainring) & causing the chain to come off….

Ooh, I know! You’re not pedalling enough! 🙂

I lost my chain twice earlier this year and it was because the rear mech was full of dried mud.