Ultegra 6800 “slipping issue”

supermurph09 Posts: 2,471
edited May 2018 in Workshop
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.


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?