Kmc advertises their chain as compatible with both. Ymmv

https://zerofrictioncycling.com.au/wp-content/uploads/2023/11/12-Speed-Chain-Compatibility-Guide.pdf

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according to that chart

the shimano chain can not be run on a sram groupset

and the sram chain can not be run on a shimano groupset

so that doesnt really clear things up

but ive sifted through dozens and dozens of posts of people running mixed brand components
but nothing is crystal clear on which chain they are using

from what i understand the sram rival axs rear derailleur requires its flat top chain
-is that correct ?

and also the rival axs rear derailleur is considered a “road bike” item
and sram eagle is considered “mountain bike” item
-is that correct ?

yes i was very close to buying the kmc x12 chain until i read this in one of their descriptions

“ This chain is compatible with 12x Campagnolo, Shimano and Sram MTB. They are not compatible with Sram road groups, this is due to a difference in pin length”

We have 2 TT bikes with AXS 12s derailleur, Ultegra 12s sprockets, one currently with a waxed Shimano DuraAce 12s chain and one with a waxed KMC 12s chain. One with wattshop Cratus single ring crank and one with k-force light cranks and Stronglight 11s rings. All combinations work fine.

When I’ve done that in past, KMC chains have worked flawlessly.

It sounds like that did pretty much clear things up. You shouldn't use the SRAM flat top chain on the Shimano cassette/chainrings. You can get away with using the Shimano chain on the SRAM road/flat top derailleur pulleys. KMC and YBN chains tend to be slightly more cross compatible, but shift slightly less well with a pure Shimano 12 speed drivetrain.
For best results with what you're trying to do, use a KMC or YBN chain and maybe swap out the derailleur pulleys for one of the aftermarket options that uses the same tooth design for both SRAM/Shimano (Kogel, for eg.).

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

thank you

i was also just thinking about running aftermarket pulleys as well
to eliminate the sram “flat top” pulleys in the rival derailleur

thank you for the help

I'd definitely use a Shimano chain if you're running Shimano chainrings and cassette; no reason not to if you're swapping pulleys out as well. Shimano chains historically have been a little faster than those from other brands.

The 12 speed Shimano chains have an increased lifespan compared to the 11 speed, at the expense of efficiency. They are reportedly significantly slower than the 11 speed, and have dropped below the Campy/YBN/KMC chains (in roughly that order). They also do not play well with the SRAM derailleur pulleys and some aftermarket pulleys, although people's tolerance for this varies.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

So im all done with the bike build
ended up working out really nice and I was able to build a nice titanium road bike for the winter on a very small budget

I found a nice Kinesis GF Racelight framset at a reasonable price
I had an older pair of Reynolds Strike 10spd wheels
(i machined the 10spd freehub to 11spd specs)

and im running the following for a 12spd groupset

12spd Sram Force AXS Etap Shifters
12spd Sram Rival AXS Etap front & rear derailleurs
12spd Shimano Ultegra 11-34 cassette
12spd Shimano 105 crank with 50-34 chain ring
12spd Shimano Dura Ace chain

the shifting is nice and crisp through every gear
didnt take much to dial it in

I will say that my Ultegra Di2 on my other 2 bikes seems to be a little quiter on the actual shifts
but this still certainly feels nice and crisp going through the gears

That is what Adam Kerin reported, although his friction data is coming from Jason Smith at Ceramicspeed. CS asked Kerin to report things in star ratings rather than in actual watts. When you say "significantly slower", I have a feeling that it's not a lot of watts. The SRAM chains are maybe 1.5-2W slower than Shimano at 250W input, and they're an outlier. On the 11s chains, there was that Cyclingtips article that reported CS's actual watt figures, and I think the delta between DA and Campy was something like 1/3 watt. I wonder if the delta between 12s DA and 11s DA is 0.3 to 0.5W or so. As in this is my wild guess at the delta, I have no insider knowledge.

I'm not entirely sure that's true. CeramicSpeed has them as within ~0.15W with good lube, and the other tests I've seen have been pretty inconclusive. And the SRAM Force 12s is slightly faster than Shimano. Do you have some definitive data showing 1.5-2W? KMC 12 is the baller fast chain, at least in the 5 hour window. Not shown is the Campy 12 chain, also supposed to be fast.

On top of that, other testing has hinted that SRAM chains get faster over time, so I'm not even sure about the 0.15W.

If going by Zero Friction Cycing's data, Force AXS and Shimano 12S are both 3.5 stars, corroborating CeramicSpeed to some level, though "stars" is an annoyingly crude metric.


Edit: I mean get faster over time at a faster rate. I have no idea which chains are A, B, C in this other CeramicSpeed test, but I'm talking about the effect shown in chain C that at least demonstrates that all chains are not equal in how they wear.

Edit: The confounding factor is some tests showing the Force chain as faster than Red, and that could have led to the 1.5-2W thing that gets repeated here all the time. Maybe that's why CeramicSpeed chose Force above. Though the duration factor mention had the hint of the AXS Red chain being slow out of the box, but getting faster quickly. I wish I could find that graph that showed the Force and Red chains getting faster quickly over the first hours of runtime. I get the sense that some combination of manufacturers get nasty about public data because a lot of graphs that used to exist are harder to find.

My intention would be for that to read as "statistically significant" which in this case is, yeah, not a lot. Certainly not a lot to be of likely importance to the OP. We're definitely well into head of a pin territory here.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

I am looking to do the same thing

How did you sync your SRAM shifters?

I don’t want to buy a blip box and don’t have access to a blip box

I do have another bike with blips but also no boop box. They were synced/paired by a LBS who built up the bike

anyway to use those blips to sync the new blips on the second bike?

I am not running any blip boxes

This is on a road bike set up
So it’s just the Shifter‘s and the deraulleurs

On my TT, Bike, and my other rode bikes I Ron Regular, Shimano di2