Ultegra 6800 group dropping chains off big ring without shifting - how come?

[alcatraz]

The whole situation sounds like a disaster.

Care to elaborate?

[Finx]

Speedplay has longer spindles available to widen the rider stance.

[mattr]

The whole situation sounds like a disaster.

Care to elaborate?

Big heavy rider who pedals like it's a weightbench, kicks the chain while backpedalling and doesn't know how to clean a chain either.

Sounds like a nightmare to me.

Oh, and a bodged driveline.

[alcatraz]

Over here we do less cleaning and more riding.

Cleaning the chain won't solve the issue. So stop with the cleaning stuff.

Every few months we put our chains in an ultrasonic cleaner, make it spotless mirror shine, and then give them a paraffine wax bath.

So don't make the mistake of associating a dark wax on a chain chain with a horrible worn drivetrains. The chain is basically new, 0% stretch, and it doesn't creep up the teeth of chanrings or cogs at all when pulling it away/or loading the pedals. The freehub spins freely, and has no sideplay. The crank has no sideplay.

Because in China where we live people don't have sheds/garages/workshop areas it can't be done after every few rides. We add wax lube until it gets a deep cleaning.

The city where we live has nearly no precipitation so 99% dry rides. It has some dust though and that's what you see collecting onto the drivetrain. If you shop owners and experts lived in dry areas you'd see these kind of drivetrains. Have an open mind please.

What about the sprinter question I posted a while back.

Is it possible an ultegra crank or chainrings isn't stiff enough?

[alcatraz]

The whole situation sounds like a disaster.

Care to elaborate?

Big heavy rider who pedals like it's a weightbench, kicks the chain while backpedalling and doesn't know how to clean a chain either.

Sounds like a nightmare to me.

Oh, and a bodged driveline.

How about some solutions to the issues rather than critisizm. If it's too complicated for you then better just let someone else post, how about it?

What's a bodged driveline? I can assure you it's all original shimano ultegra level components, with no crank/wheel/cassette play and no worn out cogs/chainrings and plenty of wear left on the chain. Derailleur hanger is straight, was done recently.

Is it possible to add more chain tension on the R8000 rear derailleur without using the B-screw?

/a

[alcatraz]

Speedplay has longer spindles available to widen the rider stance.

Thanks, this guy is using garmin vector 2 pedals.

/a

[mattr]

How about some solutions to the issues rather than critisizm. If it's too complicated for you then better just let someone else post, how about it?

I've already made some suggestions.

What's a bodged driveline? I can assure you it's all original shimano ultegra level components, with no crank/wheel/cassette play and no worn out cogs/chainrings and plenty of wear left on the chain. Derailleur hanger is straight, was done recently.

You yourself have admitted to having to tweak/finesse the front mech position to stop rub in 34/34, are the chainstays shorter than shimanos minimum spec? That can cause issues with rubbing, and ultimately unshipping chains.

Is it possible to add more chain tension on the R8000 rear derailleur without using the B-screw?

Get a clutched rear mech? https://bike.shimano.com/en-US/informat ... tures.html
About 100 euros IIRC.

[wheelbuilder]

The whole situation sounds like a disaster.

Care to elaborate?

Sure, but mattr kind of covered it. The guy is not only breaking chains, but his right foot actually comes into contact with the chain while pedaling? You stated he is a newish rider who is also heavy. It sounds like a disaster to me. A disaster to deal with a customer with these kinds of massive problems. I say customer cause I assume you are a mechanic. I ride with a Race club that has some insanely powerful sprinters. These guys don't break chains. This tells me that your guy is likely shifting under load and that is what is breaking chains. As to the derailment issue, my guess would have been a worn ring, a bent tooth, a misaligned chain link, etc. However since you stated his foot is contacting the chain, he is probably pushing the chain to the left with his heel in the chainstay area and this cause the chain to derail at the ring cause the chainline is screwed up by his foot moving the chain inward.

edit to add.........he has a 34 tooth cassette? in my book of rules this cements the status of this bike/rider as a disaster.

[TurboKoo]

How flextime is the frame?
Many of the older bikes I have had I’ve been able to drop chain slowly by putting largest gear and doing standing start to small uphill. Looking down I could see the frame flex so that chain was dropped.
If you try this be careful and cautious. Please note that you have slow cadence so you can see the chain falling off.

[alcatraz]

We are occasionally doing climbing. Therefore 11-34t cassette.

The guy will switch chainrings to new 53/39. We'll see after that if there is any improvement. We'll do it without changing chain so we'll get a bit more chain tension in 53/11.

We'll shim his right pedal outward, and move his cleats a bit.

Have you noticed ultegra6800 cranks to be unsufficiently stiff for strong riders?

We are friends. I'm not being paid. I'd like to help though.

He needa to work on his backpedaling, stop it that is. Also focus on foot angle. The guy has an ankle injury so it's a work in progress.

53t over 50t will help with giving the chain more support. The guy is riding a lot and getting stronger every week. So lets see where this goes.

/a

[alcatraz]

How flextime is the frame?
Many of the older bikes I have had I’ve been able to drop chain slowly by putting largest gear and doing standing start to small uphill. Looking down I could see the frame flex so that chain was dropped.
If you try this be careful and cautious. Please note that you have slow cadence so you can see the chain falling off.

I'm not so much concerned about the frame as it'a a Madone H2 600 carbon. Not the stiffest but stiff enough. The BB is original bb90 shimano. The crank however I'm not so sure about. I think this guy could potentially be flexing his crank and chainrings. Maybe we should try a new crank to see if there is any improvement.

Seems to me R8000 and R9100 are stiffer because the arms look beefier. What do you think?

I thank you for the suggestion and I'll the the guy to try it. Low cadence climbing in a heavy gear.

/a

[alcatraz]

Just had an idea and that's to swap cleats with lower float. That way they can help prevent the heel to hit the chain. What do you think?

Surprised it wasn't mentioned...

/a

[mattr]

IIRC the 8000 and 9x00 cranks are slightly lower profile. So any stiffness increases are going to be extremely marginal.

Swapping to lower float cleats will just mean he pops a cleat out every now and again.

You seem to have missed my reference to an Ultegra RX800 mech. It'll cope with the range better and also has a clutch which will maintain chain tension better than a conventional sprung cage.

[wheelsONfire]

Not even sure he'd make it with longer pedal axles.
But perhaps!?