I’m getting a bit annoyed with this one now. I keep thinking I’ve cracked it and then it’s back the next morning. Small jumps, just the sort of thing you might find on a energetic crosstown commute, kerb hucks and the like. It seems worse if I’m in a fairly low gear. The chain tends to jump off onto the small ring and not want to come back without shifting to near the top of the cassette. I’m becoming convinced it’s chain tension, and basically rooted in road mechs being lighter sprung than mountain.

Bike is full 5700 except CX70 crank (essentially Ultegra 36/46). Chain is two weeks old, cassette and rings show no significant wear, shifting is crisp and clean, cable tension good therefore, chain is properly sized, front mech is as low as I can sensibly get it although it’s 5700 item intended to clear a compact not 46 but I don’t think this is the issue as its a common combo.

I almost never use the low ring unless I’m riding in the Peaks or doing big proper road with real climbs. I’m seriously considering investigating a Wolf front ring and one of their rear adaptors to run a Shadow+ MTB derailleur with road levers but that seems a techy solution for something I’m sure must be simpler.

Anyone want to tell me what I’m doing wrong ?

Chain length?

As I was typing it seems an obvious option especially given the shifting needed to get the chain to get back on the big ring, but I’m always careful to measure properly. It’s a full link bigger than the wrap of the largest ring and cog, not threaded through the mech while measuring. B link is allowing about a link and a half between jockey and point of departure from cassette.

Derailleur positions in use look normal and if you actually stop you can lift the chain right back on with no shifting but a little pressure forward on the mech to detension- as normal.

I’m puzzled and frustrated…

Set the front mech up properly.

It’s either too high or not far enough over. Extra couple of turns on the barrel most likely.

Or it could be tailed in too far.

No barrels on the front of this bike. I could possibly add inline if i replaced the cable again (fresh last w/e so probably inners only and mount the adjuster on the DT stop).

Tail. I’ve got it set pretty square to the rings (as sighted down along outer plate of mech onto ring) Am I doing this wrong?

Probably cable then. Front mech sounds like it’s in the right place.

Thanks Ghostly ! I’ll investigate adjusters then. Anything much to choose between the Mpart big ridge barrel ones and the Ritchy’s?