Originally Posted by
1987cp
For years I'd thought you used a narrower chain as you go to higher cog counts (since 7- and 8-speed HG clusters are spaced more closely than 6-speeds or APII 7-speeds, and 9- and 10-speeds are said to be tighter still), but now I've come under the impression that ALL derailer systems use a chain that's 3/32" wide! Of course, there are lots of different chains specifically marketed for different cog-count shifting systems ... if they're not different in width, what IS the difference?
Until you get to 10s and 11s all chains are nominally 3/32". But the actual dimensions vary slightly, even though they all fit sprockets with teeth the same width. The difference isn't in the sprocket it inside width, but in the outside width. Starting with going from pins that protruded about 1mm beyond the outer plate, down to flush rivets, then to the plates being slightly thinner, and the tolerance tightened up to squeeze the last little bit of space in an effort to narrow the chain so sprockets could be packed closer.
There's also a difference in construction that one need be aware of. 5 and 6s chains have pins that stick out, but at 7s, they didn't narrow the chain itself but used pins that ended flush with the outer plate. That creates a safety and structural issue, in that there's no room for plates to spread, and it's easy for the plate to come off the end of the shorter pin. They resolved the issue by peening the head over the plate, or into a countersunk recess in the outer plate to lock it in place in a way that structural steel is riveted. It's important because the rivet head is critical, and that's why 7 and more speed chains cannot be closed by simply pushing a bin back the way 5 and 6s chains can.