8 speed chain on 10 speed chainset ?

[NickJP]

SRAM have used a different chain roller dia. in their 12s stuff, so it is completely incompatible with everything else.

Only the flat-top AXS road chains use the larger roller, their 12s MTB chains still use the standard roller size.

[531colin]

......
If you are using the old Stronglight cranks (or the Spa clones.....Impact, TD 2) there is a spacer between the spider and the "middle" ring, I always wanted to find out if you could get away without that on a double........but you probably want it in place with a wide 8 sp. chain?

the reason the spacer is there at all (and indeed why chainring spacing is much wider than sprocket spacing) is to make running small-small (ie. cross-chaining) viable regardless of chainring choice. In many cases it is quite possible to move the chainrings closer to one another and the only thing you lose (if that) is the ability to run in gears you wouldn't choose to run in anyway.

Chainring spacing always seems OK with the spacer, but I always wonder why there’s a spacer between the spider and the middle ring, but not between spider and granny ring.
Maybe I’m being cynical, but is it because the chainset first appeared as a double and they got the manufacturing tooling wrong, and corrected it with spacers, but by the time the triple crank came out they had got it right?
Triples assembled without spacers look comic, the 2 chainring gaps are wildly different

[Brucey]

I think that in far-off 5s/6s times. some inner (double) or middle (triple) chainrings may have had a more generous offset or tooth top profile to allow their use with 'full-fat' 3/32" chain, which is a bit wider than 7s or 8s chain is today. I remember when it wasn't that uncommon to see a chain that would 'ride' or 'skate' on the tops of the teeth of smaller chainrings, because they had the wrong offset (or tooth top profile) for a narrower modern 7/8s bushingless chain.
I suspect that, in the interim period some manufacturers may have addressed this problem by shipping cranks with a non-standardly skinny spider that would work better with 'old' type chainrings and a new chain, plus spacers so that other chainrings could also be used.

IIRC shimano went through a phase of using spacers too, but these spacers were to stay with the chainring.

The cycle industry has form for this kind of thing; retailers don't tend to take kindly to innovations that may leave them with a load of dead stock. So for example when SunTour revised their freewheels in the 1980s they were sure to make it so that the new bodies would accept the old sprockets, just so that retailers were not left with a load of (to them) useless sprockets. One side effect of this was to soon make it impossible for anyone with older bodies (like me) to find new sprockets that fitted. I guess I felt more than a bit alienated by all this, and it probably hastened my adoption of mainly shimano equipment.

[CyberKnight]

I just used vernier calipers to measure the inside width of Shimano and SRAM 12s chains: 2.1mm (that's slightly less than 11/128"). When I check some unused 8s chainrings in my spare chainring collection, the tooth thickness ranges from 2.0mm to 2.2mm. I know that some of these chainrings will work with the 12s chain, as I have that exact setup running on one bike, so if you measure with a decent pair of vernier calipers you should be able to determine if your older chainrings will work with a modern narrower chain.

im running an 8 speed chainset with a 10 speed groupset on my latest bits bike build , its all i had in the spares bin and it works fine too, i just had to buy a new 10 speed chain for another bike as for some reason i have 3 8 speed chains and no spare 10 speed .

[Brucey]

it is not at all difficult to see if chain will fit and run OK. IME if the chain runs OK and the chainset is a double it will always shift eventually.
, and for some people that is 'good enough'. However if the chainset is a triple and the ring in question is the middle one, the chain can run just fine but the shifting problems can be quite intractable. This is where you really need to have the extra clearance.