On Sat, 09 Sep 2017 06:46:59 +0200, Emanuel Berg
wrote:

John B. wrote:

"well, we do still have a few 9 speed chains
left".

Anyone feel free to elaborate on this. How and
why should the chain be different with
different cassette/chainring configurations?

And is there a "notation" do describe this?
Usually makes it easier to understand...

The rear sprocket spacing is closer as the number of cassette cogs
goes up, so narrower chains.

The over all length of the cassette is limited by the distance between
the rear drop outs as the wider the cassette the more the hub flange
on that side must be offset and thus the angle of the spokes
decreases.
--
Cheers,

John B.