As an interim measure (i.e. awaiting an Alfine hub on back order) I have fitted a 9 spd cassette & rear mech to my singlspeed P7.

Most of the time it is fine but whenever the trail is rough and I am freewheeling the chain jumps off the chainring.

Do I need some kind of chain device?

if you have a rear mech then it shouldn’t jump off or climb up the cassette (which is what it will do without the mech due to the rising profile on the teeth) I’m guessing your running this as a single speed rather than geared??

Sorry explanation wasn’t clear.

I was running it as a singlespeed, but as i am training for an adventure race I wanted some gears for longer rides and more hilly terrain.

Hence I fitted a 9spd cassette, rear mech & shifter.

Rear end is fine. It’s the chainring that it jumps off.

bashguard on outside and n-gear jumpstop on inside – ran this for ages and never dropped the chain once

By the sound of it you do. I would avoid roller under the ring type things (blackspire stinger etc), because I think this is the chain bouncing off the top (ie when there is no tension between top of chain ring and top of sprocket). That was my experience with my bike anyway (admittedly a full suss). Fixed by getting a triple, so much for simplicity. You can get a chain cage thing from DMR which acts a bit like a front mech.

chain too slack? do you just have the one ring on the front?

Yes. Only a single chainring.

Yes. It’s definitely jumping off the top, so chain tension shouldn’t make any difference.

I assume that fitting a front mech may help but if I do that I might aswell fit the whole front chainset plus front shifter.

I was just trying to bridge the two week gap between singlspeed and my alfine arriving, so dont really want to buy any kind of device.

I’m running a similair set up with a bash ring and a front mech.
Just adjust the front mech and you will have no issues, couldn’t be bothered forking out for retention device.

Thanks.

Waiting on a blackspire chainring from CRC, but will definitely stick the mech on.

Just being lazy really, as I could easily fit the whole front drivetrain, but seeing as it’ll be coming off in 2 weeks, can’t be bothered.

what clink said: n-gear and bashring, works brilliantly.

don’t go dmr doesn’t work well on a 32T chainring, and it rubs too much for XC on the extremes.

I have run a single chainring on my 456 with a N-gear Jump Stop and a bashring:

Very effective and cheap.

i ran like this on a few bikes and eventually just bought an E13 LG1 chain device.

Having said that i didn’t want to waste any cash, have just ordered a n-gear, as only £9.

Cheers for all the advice.