decided to treat my tourer to some new gearing after 2 years of heavy use. it was showing plenty of wear, and shifting was a bit off.
new 9 speed cassette, chain, jockey wheels and a new inner and middle ring.
all went on lovely in the bike stand, changing up and down the gears all as good as it should.
went out for a long ride on tuesday, after 30 minutes the gears just went to sub standard. lost all indexing, jumping up and down the cassette.
tried to fix em roadside to no avail. switched the shifter to friction mode ( xt bar end) and completed the ride in 1970's mode.

so got the bike in the stand today, issue appeared to be the chain not running very freely through the rear mech for some reason.
also a couple of stiff links on a new chain.
i spied a new 11 speed chain in my spares box. i did a search on google to see it a 11 would work on a 9 spd set up, answer was yes.
so i fitted the new 11 spd chain and bingo....... my gearing is running like new.
took the bike for a couple of mile to test it, perfect.

prettypissed that the 9 speed stuff didnt work tho. never had issues before.

Surprised the 11 speed chain worked as it's narrower than 9 speed, so it might get stuck on the cassette with a bit of dirt etc. But it's good to know - you never know when you'll have to raid the spares box!

this is what i found on the net.

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Yes, an 11-speed chain can generally be used with a 9-speed cassette and gears, although shifting performance might be slightly reduced due to the slightly narrower width of the 11-speed chain; however, you cannot use a 9-speed chain on an 11-speed cassette as it will not fit properly.

Isn't it just the outer diameter that's narrower, the inner plate dimensions are the same? So it still engages the teeth just as well...that's what I though but happy to be corrected. So shifting might suffer as it's a thinner chain trying to engage ramps on the cassette that are slightly further spaced?

Where did you get the 9 speed chain from? There are apparently quite a lot of fake shimano chains out there...

NewRetroTom wrote: ↑Fri Feb 28, 2025 11:55 am Where did you get the 9 speed chain from? There are apparently quite a lot of fake shimano chains out there...

Was also about to reply this. A mate had a load of problems with KMC chains recently, turns out they were all fake although you need to do some checks against pics / vids on the internet to be sure as the packaging is so convincing. A chain stretch tool is also a good indicator if it is stretched before even fitting.