I know that you should use a 3/32 chain with a 3/32 cog and the same goes for a 1/8 size. But I read some posts of people using different chains of different speeds and also mixing width sizes. Are the older 8 speed chains more forgiving? What do you think is the best set up for a smooth fixie?

I know that you should use a 3/32 chain with a 3/32 cog and the same goes for a 1/8 size. But I read some posts of people using different chains of different speeds and also mixing width sizes. Are the older 8 speed chains more forgiving? What do you think is the best set up for a smooth fixie?

You can use a wide chain with narrow rings and cogs, but you can't use a narrow chain with wide rings and cogs. Smoothness on a fixie is a function of (a) a good straight chainline; and (b) proper chain tension (not too loose and not too tight). If you get the chainline right, a fixie chain doesn't have to be as "forgiving" as on a derailleur bike, because the chain doesn't need to flex sideways. Chains last a long time on fixies, unless you overdo the tension.