Ultegra 6800 “slipping issue”

supermurph09

Had an issue with what I believed to be the chain slipping, essentially under load it would “slip” making a loud crunching noise and often the chain would come off.

Result, new chain on, new gear cable, everything indexed perfectly and still the same issue. I’ve swapped wheels and cassettes, still same issue.

Diagnosis.

Issue only occurs when in big ring, issue occurs when getting OOTS, could be from a standing start or when looking to stand up and push on, not always with many watts being applied. Also can occur when at higher power on the flat, even more so if over bumpy ground (could be coincidental). However I can be seated and put 400-500W and all fine. In all instances this can cause the chain to come off, more likely when OOTS.

Bike: Canyon Ultimate 4 years old (12,000 mile, + turbo)
Group set: Ultegra 6800, original chainset, jockey wheels, RD. Bike always cleaned and lubed.

Any ideas what is causing this?

mike1-2

Worn big ring. Get a new one.

shirley_basso

Big ring worn out most likely. Put it in a turbo trainer and slowmo video it.

Happened to me twice now. I think the 11sp chainrings are softer than the old 9 speed.

I think the groupset in general is more sensitive to worn chains.

supermurph09

The chain ring suggestion makes most sense to me.

supermurph09

Would an R8000 chainset be a straight swap or would I need a new BB as well?

milemuncher1

I had a similar issue with my 6800 Ultegra GS bike. The big ring was slightly bent, I used it as an excuse for a new Crankset. The R8000 is a straight swap.

supermurph09

Thanks guys, much appreciated.

Vino'sGhost

Is it cheaper to change a chain set than the chainring?

shirley_basso

Genuinely, sometimes, yes.

imafatman

Supermurph09 wrote:

Would an R8000 chainset be a straight swap or would I need a new BB as well?

Though after 4 years and 12k miles you might want to check the BB to make sure it's still good whilst you are going to the effort of fixn for £20-30 they are pretty much a consumable item, i bet your jockey wheels are also somewhat knackered.

svetty

Could be frame flexing under load?

supermurph09

Svetty wrote:

Could be frame flexing under load?

Would you still not get this when out the saddle in the little ring though?

redvision

Supermurph09 wrote:

Svetty wrote:

Could be frame flexing under load?

Would you still not get this when out the saddle in the little ring though?

Easy to figure out. How long has the problem gone on for? Was it there when you got the bike? if not it will be a worn chainring.

No need to replace the whole chainset, you can just replace the big ring (if you want to save a few quid).

milemuncher1

redvision wrote:

Supermurph09 wrote:

Svetty wrote:

Could be frame flexing under load?

Would you still not get this when out the saddle in the little ring though?

Easy to figure out. How long has the problem gone on for? Was it there when you got the bike? if not it will be a worn chainring.

No need to replace the whole chainset, you can just replace the big ring (if you want to save a few quid).

The difference in price for ‘official’ Ultegra rings, and ‘official’ full cranksets is not that great, it’s often worth paying an extra couple of quid, and getting a pair of rings, and cranks.

supermurph09

£85 for outer chain ring from wiggle.

£153, for R8000 chainset which does include non-drive side crank arm from Tweeks cycles.

I think I’m favouring the latter.

svetty

Supermurph09 wrote:

£85 for outer chain ring from wiggle.

£153, for R8000 chainset which does include non-drive side crank arm from Tweeks cycles.

I think I’m favouring the latter.

It's your money of course but if the inner ring and spindle aren't worn you are paying a lot more for components that aren't subject to wear........

supermurph09

Update:

Borrowed a club mates chainset, bike shop quickly popped it on, I did a test up and down the road outside (albeit with trainers on) and all seems ok. So, subject to a proper test it looks like it's a worn chainring, thanks for the suggestions.

I'll report back when 100% tested.

Vino'sGhost

Shirley Basso wrote:

Genuinely, sometimes, yes.

Madness

supermurph09

Well, some things in life are never smooth are they...

Mates chainset was different bolt pattern, new chainring ordered from Wiggle!