Di2 dropping chain

sullzz

So I have ultegra 10 speed di2 fitted on my bike , it has dropped the chain twice during races , both time from the big ring once it hopped off onto pedal side and 2nd time it dropped of to bottom bracket side , it didn't over shift the first time , both times it happened when out of saddle pushing which is not great as on Sunday it caused me to whack my knee off the bar end , luckily I was to the side of the road and could steer into the grass verge out of the other riders way .
The crankset I have is 11speed but was reassured this is not the issue , 2 bike shops could not find a fault , anyone else have any ideas what the issue could be , the crankset , chain and cassette are new .

kayaksurfbum

Could frame flex cause that?

I remember reading that is used to happen to pros allot with certain frames.

sullzz

kayaksurfbum wrote: »

Could frame flex cause that?

I remember reading that is used to happen to pros allot with certain frames.

Can't imagine I'm putting out that much power :P
Frame is a Ridley Noahfast if that makes any difference

Inquitus

Worn Chainrings / Stretched chain used to cause that for me, replaced and problem gone.

sullzz

Inquitus wrote: »

Worn Chainrings / Stretched chain used to cause that for me, replaced and problem gone.

Ive a new crankset , chain and cassette fitted only a couple of months ago so I can rule them out

Unknown Soldier

sullzz wrote: »

So I have ultegra 10 speed di2 fitted on my bike , it has dropped the chain twice during races , both time from the big ring once it hopped off onto pedal side and 2nd time it dropped of to bottom bracket side , it didn't over shift the first time , both times it happened when out of saddle pushing which is not great as on Sunday it caused me to whack my knee off the bar end , luckily I was to the side of the road and could steer into the grass verge out of the other riders way .
The crankset I have is 11speed but was reassured this is not the issue , 2 bike shops could not find a fault , anyone else have any ideas what the issue could be , the crankset , chain and cassette are new .

So you are in the big ring (53?) and shifting at the rear and the chain is coming off? at the front?

sullzz

Unknown Soldier wrote: »

So you are in the big ring (53?) and shifting at the rear and the chain is coming off? at the front?

1st time I definitely didn't shift at the rear and it came off , on Sunday I don't think I did either but there is a possibility I might have as we had just come around a bend .
What are you thinking ?

Unknown Soldier

sullzz wrote: »

1st time I definitely didn't shift at the rear and it came off , on Sunday I don't think I did either but there is a possibility I might have as we had just come around a bend .
What are you thinking ?

Well you have had a shop look at it so they should know their stuff. But I'd be checking the height & alignment on the FD first. My Di2 from the "factory" has about a 1-2mm gap above the big ring, and is perfectly in line/parallel with it too.

nordicb

Perhaps too much chain slap, maybe it is too long? Does rear derailleur have a b-screw?

omri

Might be a long shot but arent shimano chains directional - maybe its on the wrong way?

andy69

I recently had two incidents where the chain came down from the big ring to the small ring 'by itself'. Second one I had the wife and her friend on my wheel so nearly taking them out gave me more than a bit of a fright - can you imagine the abuse I'd have gotten!!!

I'm certain I didn't accidentally tip off the button...having said that, with bumpy roads and what have ye, it might be possible my fingers did tip it, but I'm fairly sure it just dropped down itself.

Wonder if there's a little bug in the firmware...?

Was thinking then maybe the mechanic that set it up might have done something slightly wrong, but I think the system is pretty foolproof/failsafe with no wires crossing that might accidentally trigger a change - they just all plug into their little sockets I think.

It's a 2016 bike, 4,000km on it and the chain is at 0.25 so there's nothing worn that might cause it.

Maybe water ingress? would imagine that they'd have it pretty sealed though

sullzz

omri wrote: »

Might be a long shot but arent shimano chains directional - maybe its on the wrong way?

Not the case here

sullzz

Unknown Soldier wrote: »

Well you have had a shop look at it so they should know their stuff. But I'd be checking the height & alignment on the FD first. My Di2 from the "factory" has about a 1-2mm gap above the big ring, and is perfectly in line/parallel with it too.

Yeah that's all the first things I checked

sullzz

nordicb wrote: »

Perhaps too much chain slap, maybe it is too long? Does rear derailleur have a b-screw?

Doesn't appear to be much chain slap happening , not too much slack on the chain either .

Crocked

omri wrote: »

Might be a long shot but arent shimano chains directional - maybe its on the wrong way?

That's interesting, never heard of that before. I had a problem on a new bike, thought it was bottom bracket related. Sent it back to be checked and apparently the bike was stripped and rebuilt and given the all clear. Bike arrived back with exactly the same problem.

Got an different mechanic locally to look at it and pretty much straight away ID it as the chain. Said he'd never use Shimano chains (I'd never had an issue with them before) and he put a SRAM one on, issue gone. Wondering now if the factory installed my original chain the wrong way around.

Sorry to go off topic.