Chain jumping off middle ring

[Dec66]

I have a triple set up on my commuter bike, and as I don't like cross chaining up the steeper hills I pop it off the big ring to the middle (50 to 39). However the chain seems to try to jump again onto the inner one despite my being only halfway down the cassette (19t or so).

Before it does, there's a noticeable "click" at every 3 or 4 turns of the crank.

Stiff link, maybe? Or one link too many/few?

 

[steve50]

Is your front derailleur set up properly, I'm thinking as you go down the gears on the cassette the chain could be catching the fd causing it to push the chain down onto the small chain wheel. I would start at the fd , make sure all is aligned correctly and the chain wheels are straight before looking at the rest of the drive train. I would have thought if it was stiff or damaged links in the chain you would notice it jumping / slipping at the cassette too.

 

[raleighnut]

I think it may need a touch more tension in the cable, to test for this put it onto the inner 'granny' ring and see if it changes up easily without needing a bit of an extra shove then check it is sitting central on the middle ring.

 

[Ajax Bay]

there's a noticeable "click" at every 3 or 4 turns of the crank.

If your middle chainring is 40t (say) that's 20 links. If the click happens every 3-4 turns of the crank that's getting on for 5 1/2 [Edit actually every 2.8 turns: chain 56" long divided by 20"] and that'd be a click for every run through of the chain. So likely this is a 'particular link' problem/issue, not an FD issue, with the result of the chain throwing off onto the inner, perhaps pushed by the outer side of the cage. Might be solved by a little more cable tension, but you need to track down what's making that click. It's not the number of links btw.

 

[lutonloony]

If your middle chainring is 40t (say) that's 20 links. If the click happens every 3-4 turns of the crank that's getting on for 5 1/2 and that'd be a click for every run through of the chain. So likely this is a 'particular link' problem/issue, not an FD issue, with the result of the chain throwing off onto the inner, perhaps pushed by the outer side of the cage. Might be solved by a little more cable tension, but you need to track down what's making that click. It's not the number of links btw.

You totally lost me there. I have no idea what you mean by 5 1/2. Could you explain please for the hard of learning

 

[Dec66]

Thanks chaps, I've been told cable tension but that click, which feels like the chain's about to throw when it happens, makes me think there's a stiff link.

The mech rub from the FD is quite shocking, too; since I had the cassette changed out from a 12/25t to an 11/28t it rubs on the big ring (when the rear cassette's on the 11, the 13, or the 28) and on the granny (in pretty much any ratio apart from the three "toothiest"). I know triples can be hard to set up but that's just not right at all.

I think another LBS needs to look, because I'm crap at mechanicals. My dad would be ashamed of me.

 

[Ajax Bay]

I have no idea what you mean by 5 1/2. Could you explain please for the hard of learning

I got the maths wrong (have edited my post above) but the analysis still applies. An average length for a chain is (say) 112 half links or 56 inches and a tooth on one full turn of the middle chainring (40t) will travel 20 inches. So the chain completes a 'cycle' every 56/20 turns of the cranks: every 2.8 turns. OP said:

Before it does [throw the chain off the middle onto the inner chainring], there's a noticeable "click" at every 3 or 4 turns of the crank.

So the click frequency is likely coincident with one particular link of the chain contacting something (could be the FD cage).

 

[lutonloony]

I got the maths wrong (have edited my post above) but the analysis still applies. An average length for a chain is (say) 112 half links or 56 inches and a tooth on one full turn of the middle chainring (40t) will travel 20 inches. So the chain completes a 'cycle' every 56/20 turns of the cranks: every 2.8 turns. OP said:

So the click frequency is likely coincident with one particular link of the chain contacting something (could be the FD cage).

Ok, get it now ( although I would have just stayed in links/teeth) but maths makes sense

 

[Nigelnaturist]

Thanks chaps, I've been told cable tension but that click, which feels like the chain's about to throw when it happens, makes me think there's a stiff link.

The mech rub from the FD is quite shocking, too; since I had the cassette changed out from a 12/25t to an 11/28t it rubs on the big ring (when the rear cassette's on the 11, the 13, or the 28) and on the granny (in pretty much any ratio apart from the three "toothiest"). I know triples can be hard to set up but that's just not right at all.

I think another LBS needs to look, because I'm crap at mechanicals. My dad would be ashamed of me.

A triple is no harder than a double same procedure for both, if chain is rubbing on the outside of the FD cage on the smaller cogs tension ( most likely from the other symptoms) or hi-stop screw needs a tweak, most brifters have a trim function which allow a half way stop between front rings for example on the large ring a slight touch on the changer will move the FD inwards slightly allowing to use the larger rear cogs with out chain rub, likewise on (@raleighnut ) an inner ring the same is true as you tension the cable with the shifter a slight click is felt as you go to the right with the lever.

 

[Ajax Bay]

What is the FD model?