I have on occasion come across shifting issues on rear gears where the component parts are in good condition and the gearchange is good on the majority of the block but one or two particular shifts has been poor, over and over again. No amount of remedial action to cables or checking of alignment makes any difference and the chain wear elongation indicator shows less than .75%.
I am now beginning to think that in these cases the chain is indeed worn out but the problem is not elongation but flexibility. It seems to me that a chain needs to have a degree of sideways movement otherwise no gearchange will occur but it also needs stability so that small movements in the jockey wheels result in movement of the chain rather than undue flex between links. In most gear combinations the jockey wheel is close enough to the cassette to reduce the potential for too much link-to-link flex but cassette ratios vary and the pulley wheel height adjustment screw can only do so much given that the parallelogram angle is fixed and will not always match the outer profile of the cassette. the result of this is that on some gear combinations the top jockey wheel is far enough away from the cassette that a greater than ideal number of links are present between pulley and cog and the push of the mech is absorbed by the over flexible chain. Now, this is just my brain doing its bit in a moment of idleness and I don't have a bike to try my theory out on right now.
In future I would like to measure the lateral flexibility of a chain but does anyone know of a set of guideline limits for this?
A thought about chains
A thought about chains
The older I get the more I’m inclined to act my shoe size, not my age.
Re: A thought about chains
I think you are right about lateral flexibility but it isn't the only thing that affects shift quality. Just compare a new chain with a borked one; near the end of their life worn chains are so laterally flexible that they can practically be wrapped into a complete circle.
Other things that are very important include
a) exact shaping of side plates (some chains just shift better than others; chalk and cheese when they are both new)
b) matching of shifter to cassette.
c) alignment of RD; note that the tolerances for camber and toe allow ~0.5 degrees in one direction only.
On the point b) all cassettes have at least one 'bad transition' in them, eg where it goes from 2-ramp to 3-ramp sprockets. However this may occur in a different place depending on whether it is a 'road' or 'MTB' cassette (this is certainly the case with shimano 9s cassettes). Accordingly this is either dealt with by having very slightly non-uniform cable pulls in the shifter, or very slightly uneven spacing in the cassette.
So for example it is common to use a shimano 'road' 9s shifter with a 'mtb' cassette on a touring bike, but actually this is not a combination that shimano recommend; the reason is (I think) that the cable pulls are non-uniform in 9s shifters, but in a way that differs between 'road' and 'mtb' ones. When everything is new it all works fine, but when it is getting a bit worn it is more commonly the case that you see a bad shift in the middle of the cassette, because the parts are not really a perfect match.
cheers
Other things that are very important include
a) exact shaping of side plates (some chains just shift better than others; chalk and cheese when they are both new)
b) matching of shifter to cassette.
c) alignment of RD; note that the tolerances for camber and toe allow ~0.5 degrees in one direction only.
On the point b) all cassettes have at least one 'bad transition' in them, eg where it goes from 2-ramp to 3-ramp sprockets. However this may occur in a different place depending on whether it is a 'road' or 'MTB' cassette (this is certainly the case with shimano 9s cassettes). Accordingly this is either dealt with by having very slightly non-uniform cable pulls in the shifter, or very slightly uneven spacing in the cassette.
So for example it is common to use a shimano 'road' 9s shifter with a 'mtb' cassette on a touring bike, but actually this is not a combination that shimano recommend; the reason is (I think) that the cable pulls are non-uniform in 9s shifters, but in a way that differs between 'road' and 'mtb' ones. When everything is new it all works fine, but when it is getting a bit worn it is more commonly the case that you see a bad shift in the middle of the cassette, because the parts are not really a perfect match.
cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: A thought about chains
I agree with the above posts,but to add that STI's both road and MTB offer quite precise overshifting to larger sprockets that minimises the effects of chains with side slop.
Whereas d/tube and b/end levers don't,well they do but with nowhere near the same precision as STI's.
Shifting to a smaller sprocket doesn't have the same shifting problems with a chain with side slop as it's falling off the big cog with the assistance of ramps.
Whereas d/tube and b/end levers don't,well they do but with nowhere near the same precision as STI's.
Shifting to a smaller sprocket doesn't have the same shifting problems with a chain with side slop as it's falling off the big cog with the assistance of ramps.
Re: A thought about chains
Brucey, I completely understand your comments about worn chains and I would like to clarify my original post. I should really had made it clear that I was drawing attention to the fact that the chain elongation tool has its uses but cannot indicate wear in all cases. I am going to quizz the owners of the bikes further as to their gear discipline because I believe that it's quite possible for a non-elongated chain to be worn out. Such a thing could happen if the owner is in the habit of cross-chaining regularly. If that is the case I can see that lateral deflection should be the primary chain wear indicator for 1x systems and that much more frequent chain replacement is to be recommended.
The older I get the more I’m inclined to act my shoe size, not my age.
Re: A thought about chains
peetee wrote:Brucey, I completely understand your comments about worn chains and I would like to clarify my original post. I should really had made it clear that I was drawing attention to the fact that the chain elongation tool has its uses but cannot indicate wear in all cases. I am going to quizz the owners of the bikes further as to their gear discipline because I believe that it's quite possible for a non-elongated chain to be worn out. Such a thing could happen if the owner is in the habit of cross-chaining regularly. If that is the case I can see that lateral deflection should be the primary chain wear indicator for 1x systems and that much more frequent chain replacement is to be recommended.
I don't think so. A chain that is worn laterally will also be worn longitudinally. I also don't think lateral flex of a chain is that important either.