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.
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