Chain coming off chain ring on rough ground

[ade towell]

Hello I have converted a 10 year old hardtail with a Toseven DM02 mid drive torque sensor motor. Am very happy with the performance of the motor, but having spent a lovely day out in the Peak district, one thing that I found quite irritating is the amount of times the chain came off the chain ring on rough terrain. It's a 9 speed Shimano Acera M390 derailleur without clutch - I don't think Shimano do one with 9 speed. I see Microshift do but it's quite expensive and not sure if it would work?

https://www.sjscycles.co.uk/derailleurs-rear/microshift-advent-rdm6195m-9-speed-rear-derailleur/

But I don't recall the chain coming off before I fitted the DM02 with 42t chain ring. It had a triple front derailleur maybe that helped keep it on?
The chain is the right length but is quite worn so maybe that doesn't help. But gear changes are still fairly snappy and don't slip so haven't replaced chain yet as imagine will need to change cassette too.
Have read that narrow wide chain ring also helps, I don't think the one Toseven supply with is narrow wide it seems flat? Also maybe the spring tension in the derailleur isn't as good as it was.
Am wondering if getting derailleur with clutch will solve the issue completely or if the DM02 chainring being flat not narrow wide would also need replacing? I will replace chain and cassette soon but can't imagine that will suddenly stop the chain falling off if I don't change derailleur and chain ring. Anyone help? Thanks

 

[T4tomo]

It had a triple front derailleur maybe that helped keep it on?

you have answered your own question, the front mech kept the chain in place.

Of course the chain will fall off on bumpy ground, the Rd swings a bit an loosens the chain.

Easiest fix is one of these chain guides.

clutched derailleurs and narrow wide chainrings will also work but more expensive.

 

[ade towell]

Great thanks will give that a go, being a tight arse was hoping for such a cheapish solution

 

[Ajax Bay]

https://electric-bike-conversions.c...250w-350w-500w-torque-sensing-mid-drive-motor

 

[ade towell]

https://electric-bike-conversions.c...250w-350w-500w-torque-sensing-mid-drive-motor

Yes that's the motor I have although got it for £260 from PSW Power in Germany, there weren't any UK suppliers when i got it but that's quite a hike on the price

 

[si_c]

Have read that narrow wide chain ring also helps, I don't think the one Toseven supply with is narrow wide it seems flat? Also maybe the spring tension in the derailleur isn't as good as it was.
Am wondering if getting derailleur with clutch will solve the issue completely or if the DM02 chainring being flat not narrow wide would also need replacing? I will replace chain and cassette soon but can't imagine that will suddenly stop the chain falling off if I don't change derailleur and chain ring. Anyone help? Thanks

A clutched derailleur will help, but less than a narrow-wide chainring, I run a 1x setup on my hardtail MTB and with a narrow-wide and no clutch it doesn't come off, even on quite rough trails.

Not sure what you mean by a flat chainring, narrow-wide refers to the width of the teeth on the chainring, every other one is thicker and you can't fit it in the narrow section of the chain, hence the name. It should be easy to see if you have a chainring like this or not - if not then replacing it would be my first port of call.

 

[Sharky]

+1 for using a narrow/wide chain ring.

 

[Sharky]

The chain is the right length

Is this the chain that was on previously with the triple chain set? Did you remove any links to shorten the chain?

 

[ade towell]

A clutched derailleur will help, but less than a narrow-wide chainring, I run a 1x setup on my hardtail MTB and with a narrow-wide and no clutch it doesn't come off, even on quite rough trails.

Not sure what you mean by a flat chainring, narrow-wide refers to the width of the teeth on the chainring, every other one is thicker and you can't fit it in the narrow section of the chain, hence the name. It should be easy to see if you have a chainring like this or not - if not then replacing it would be my first port of call.

Yes sorry my bad terminology - flat as in the teeth are all the same. Have ordered the chain guide now so will see if that helps otherwise will then see if I can find a narrow wide chain ring that will fit the DM02. Thanks

 

[ade towell]

Is this the chain that was on previously with the triple chain set? Did you remove any links to shorten the chain?

Yes I removed some links

 

[T4tomo]

A clutched derailleur will help, but less than a narrow-wide chainring, I run a 1x setup on my hardtail MTB and with a narrow-wide and no clutch it doesn't come off, even on quite rough trails.

Its a question of whether there is a N/W CR to fit that aftermarket motor crank though - we have no idea what BSD it is etc.?

 

[Ajax Bay]

Its a question of whether there is a N/W CR to fit that aftermarket motor crank though - we have no idea what BSD it is etc.?

Well the OP can easily measure 'tween holes' to ID BCD. Looks like 5-bolt 110mm. A quick DuckDuckGo suggests plenty of choice.

 

[ade towell]

Yes the one I got with the motor was indeed 5 bolt 110mm with 10mm offset to help with chainline (which on that point works a treat)