I've got specifics to my situation, but the question is general: if you have a fixie or SS with either a 1/8" cog or 1/8" chainring, it's necessary to use a 1/8" chain. Is there any downside to having the other gear (chainring or cog, respectively) be a 3/32" instead of also being 1/8"?

Two combinations:
* 1/8" chain and cog, 3/32" chainring
* 1/8" chain and chainring, 3/32" sprocket
Compared to 1/8" chain, cog, and chainring

Obviously, a 1/8" chain will interface with a 3/32" cog or chainring. The only possible downsides I can think are noise (don't know that it would be noisier, but I seem to have heard this somewhere) and decreased chain durability (since the chain could sag to one side or the other on the cog or chainring with narrower-than-necessary teeth), or greater likelihood of derailing (which is a low possibility to begin with though).

Here's some threads on this same question. Nothing much specific in any of them - no problems reported, but no definitive statements either.
https://www.bikeforums.net/singlespeed-fixed-gear/281355-1-8-chain-3-32-cog.html
https://www.bikeforums.net/singlespeed-fixed-gear/273546-3-32-chain-cog-1-8-c-ring.html
https://www.bikeforums.net/singlespeed-fixed-gear/271957-will-3-32-wide-chainring-work-1-8-wide-chain-cog.html

I run big chains with 3/32" gearing. Not really any noise, BUT, it seems like the chain becomes slack sooner. Don't know what thats about.

on one of my builds, I use a 1/8 chain with a 3/32 rear cog and 1/8 chainring...no problems and running quiet..I've read about the noise factor and durability, but I sure don't hear anything and as far as durability I don't see a problem yet (around 500 miles) so too soon to tell

My buddy and I just put together a SS roadie with a 3/32" cog and chainring and a 1/8" SRAM pc-1 chain. The bike is super quiet on our early am rides and he now has well over a few hundred miles on it as it is his daily commuter.

Neither of us see any problems arising out of this set-up

Craig

Though I have an all 1/8" chain/cog/chainring combo, I've seen mentioned here that an all 3/32" combo is quieter. If you experience any noise, just use Phil's tenacious oil. I did and makes my bike very stealthy. (there are other things one need to do after applying the tenacious lube)

Now, a wide chain and narrow chainring or cog, would seem like it may create noise, specially when chainline isn't perfect. Try the above solution. Otherwise, I don't think there is anything wrong using your setup.

Tenacious is a pretty terrible chain lube, it doesn't really penetrate and it picks up a ton of crap

that was my thought too - if you could get it to penetrate, and wipe it all off the outside, out would be pretty good (perhaps similar to factory lube), but neither of those conditions are likely. I use tenacious oil for lots of things, and really like it, but chain lube hasn't been among those applications.

It really is. I am using it.

how do you get it to penetrate? and how do you effectively wipe off the tenacious excess so it's not a dirt magnet for your chain?

It's pretty tedious work.
1] I unloop the chain, hook it up to a piece of paperclip, hang the whole thing on my bike workstand (extend the workstand as tall as possible).
2] I clean the chain using the unleaded fuel stored in my gas can.
3] Clean between link rollers using pipe cleaners (as in tobacco pipe).
4] The chain dries off pretty fast. I drip the tenacious starting from the top down to the bottom.
5] Let it sit overnight, about 8 hours for me. For some reason, it makes its way through the crevices. Wipe down excess.
6] Clean each link once more with pipe cleaners (changing often). Save the used unleaded fuel to dip the pipe cleaners for getting rid of the excess tenacious they have caught and reuse.
You now have an almost factory-like lubed chain.
Don't get me wrong, you still have a cleaner chain using ProLink, but you'll have a chain that is super quiet.

I'm running a 1/8" chain on a 1/8" chainring and a 3/32" rear cog. I can't hear a thing while riding, but the cog/chain combo is audible when it's up on the stand.

I ran 1/8" chain as the timing chain on our tandem for a few years with a 3/32" ring on the front and a 1/8" ring on the back (kid-back with a child's crankset back there). Never had any problems and it seemed as smooth and quiet as when everything was 3/32".