My chain sits on the chainstay of my full-susser, despite measuring the length correctly (fully compressed travel – big cog to big and then add two links). It only happens in small cog to small and is the only gear that slips, should I just shorten the chain slightly?

If you shorten the chain then you run the risk of ripping the mech off in the ‘big big’ gear combination (which you’re not supposed to use in a 3×9 setup anyway). Presumably it wasn’t like this before? If so, have you changed the rear mech i.e. gotten a medium length cage, or have you changed the size of the chainrings or cassette recently?

Wasn’t like it before. Just bought a new chain, I’ve thrown the old one away for comparison.

What are you doing in small to small gear ? Not good for your chainline that.

Small COG to small COG. You never use 10th gear? Leave off.

I never use small-to-small no.

Small COG to small COG. You never use 10th gear? Leave off.

I think you might be in the minority if you use small/small, I don’t personally as I was lucky enough to be taught how to ride a bicycle when I was a child.

if I go small to small, not that I do, then my chain touches the base of the front mech. Not a gear for normal use, as timmys says

If the chain is straight and it is resting on the chainstay then it was like that before, you just didn’t notice. Use a straight edge if you aren’t sure. Bet it doesn’t touch when you are actually static on the bike though but obviously could when moving.
Shorter chain shouldn’t affect the top run but a mech that isn’t putting enough tension on the chain could, sure it is routed through the jockey wheels correctly? Not run around the little tab bit that always catches me out…

OP, a sticking freehub or loss of tension in the rear mech can result in the top half of the chain resting on the chain stay whilst freewheeling. Does the chain sag when the bike is static?

If it is, and you haven’t changed anything else, and you didn’t have this problem before, then I guess the new chain must be longer than the old chain (or at least I can’t think of anything else). But before you start shortening the chain, I’d double check the original measurment. It sounds like you was measuring the chain length the correct way, but it’s easy to slip up and mark the wrong length. Make sure you don’t have the chain routed through the rear mech when you are doing the measurement.

It’s a pity you don’t have the original factory-fitted chain for comparison. A lesson to be learnt there about not throwning away old stuff until you’re happy the new stuff works ok!

Sum – Member
loss of tension in the rear mech

This is what I was going to suggest. I’ve had that a couple of times and need to either give it a good going over with light lube or do a complete dismantle, clean and regrease.

Be sure when you stated big-big and 2 links you meant 2 rivets and not 2 complete links.

PaulD

Useful video here for setting up your chain to the right length.

Okay solved it. Before I swapped the chain I had un-screwed the chain tensioner on the rear mech to get the jockey wheel closer to the cassette. Screwing the adjuster back a few turns noticeably took the slack out and it now runs sweet.

thanks for the vid, guilty of annihilating my 1 week old XO short mech this morning,

had to ride it 5 miles home with only half the lower jockey wheel intact, made a noise like a metronome !!

though no problem as i have some spare jockey wheels, but unfortunately i managed to delaminate the carbon cage during the ride, bummer.

Okay solved it. Before I swapped the chain I had un-screwed the chain tensioner on the rear mech to get the jockey wheel closer to the cassette.

D’oh! So much for not having changed anything else/not having the problem before! Anyhoo glad you got it working now. 😀

Thx sum. I made the change to the adjuster weeks ago which at the time didn’t seem to do anything. It didn’t occur to me until this afternoon. Thx for everyone’s input.