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I'm installing a Shimano 1x12 setup and following the instructions. When measuring the chain it says to put the chain around the largest sprocket and largest chainring, measure to the zero point, and add 5 links + the quick link (for a hardtail).

Does this mean the chain is not meant to be run through the pulleys when measuring the chain length?

Here are the instructions I'm following - https://si.shimano.com/pdfs/dm/DM-MARD001-02-ENG.pdf

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  • You can run it through or not -- for most derailers it makes little difference (maybe a link or two), provided you stretch the derailer all the way out. But stretching the derailer all the way while measuring is tricky, so it's easier to just add the extra 2 links (which the "add 5" rule incorporates). If you do have a wonky derailer that can't stretch all the way out it may be better to measure with the chain threaded through. Feb 27 '20 at 22:44
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Don't run the chain through the derailleur. The Shimano instructions would explicitly tell you to do that and the diagrams would also show it.

In general the chain does not have to be run through the derailleur when measuring length. See this Park Tool video. This is because the chain takes a fairly straight path through the derailleur cage when on the largest chainring/sprocket. It's recommended to do it this way to avoid getting whipped in the face with the chain.

The Shimano instructions say to add more links than the Park Tool video, but I'm sure that's to take account of Shimano's specific 1x12 drivetrain design.

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  • The confusing part was on the page after the part about running the chain over the largest sprocket/chainring, the instructions show how to run the chain through the derailleur. Feb 27 '20 at 22:05
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    @BrettDeWoody, the instructions for run the chain through the derailleur are for after you cut the chain to size. Feb 28 '20 at 0:56
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5 links doesn't seem like enough if measured without the derailleur. Ive never done it that way. But yes, it does have to run through the pulleys, maybe they omitted that in the explanation? Pulleys range in size, and cages range in length, hangers vary a little too, effecting the overall position of the der on the frame. I have had fantastic success by putting the chain on the biggest ring and cog, through the der of course, then cutting chain at the shortest length that it shifts easily onto the biggest ring/cog combo yet has no slack on the smallest combo.

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  • That's what I thought, but according to this Park Tool video this method is common - youtube.com/watch?v=O0YibMDWBAw Feb 27 '20 at 21:38
  • this is interesting. Ive never considered doing it this way, but I have always had a great result. I think I am going to check my chains and see how close to the "correct" length Ive been achieving. I may keep doing it my way, but I guess I've learned something new here.
    – bradly
    Feb 28 '20 at 1:47

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