Will an 1/8" chain and cogs wear slower than 3/32" chain and cogs for single speed / fixed gear setup? What about using an 1/8' chain mismatched on 3/32" chainring and cogs?
I don't remember where, but I read once that because a 3/32" chain is more flexible laterally than a 1/8" chain, it is more tolerant of imperfect chainlines. This makes sense to me, but I haven't seen any numbers to support it. So with an imperfect chainline you might see faster wear with 1/8".
I suspect the difference in wear is imperceptible, especially with a steel cog. The combination of a 1/8" chain, imperfect chainline, and an aluminum 3/32" cog would probably be where you'd see the most increase in wear because you add a slight bit of play where the chain interfaces with the cog, but I still doubt you'd notice much additional wear.
Just from personal experience 1/8" chains are less forgiving to any misalignment with the chain-ring and cog. You can really feel it (and hear it) if you place a 1/8th chain over an 3/32" chain-ring/cog. Constant use in that manner leads to things breaking, even if it's just your sanity over the clicks and pops you can hear as you pedal.
However, because 3/32" are more flexible, they seem to keep quiet and hide your misalignment issue. I've only ever broken one chain-ring and it was a 3/32".
In short, a perfectly set chain setup at 1/8" I believe would outlive an 3/32" setup. Or at least has so far on my fixed gears.
I personally think that the wear issue is not as simple as one size chain being better than the other. Whilst this may be the case, it will all depend on the quality of the products involved ie cog, chainring and chain.
Your chain line is very important in a situation like this. Also if you use a flip flop rear hub your wheel has to be symmetrical.... So when you flip it around it does not affect the chain line. For my chain line I use a Phil Wood BB which gives the most adjustment. I run a 1/8 crank (Paul Royal Flush). 1/8 chain. 1/8 Phil Wood track cog but I use a WI free wheel cog which is 3/32. They are both 18 teeth so when I flip the hub the tension is pretty close Hope this helps Chuckmeister