I came across these figures on Wikipedia and I don't think the conductivity is going to matter much when you look at the actual numbers. The different restiveness for Platinum = 1.06×10^−7 Ωm vs Copper = 1.68×10^−8 Ωm.
The total resistance of the copper/platinum/iridium conductor is maybe billionths of an ohm. Meanwhile, it's in series with the spark plug wires, which typically have a resistance of 10,000 to 15,000 ohms. So you're talking about a difference between 10000.000000001 ohms and 10000.000000006 ohms. The difference between the conductivity of copper and platinum is totally irrelevant.
Platinum is used because it's more durable, not because it's a better conductor. (Same for gold-plated audio cable connectors, incidentally.) This allows it to be made into a narrower electrode without eroding away as quickly as copper would, to make it sharper (higher electric field strength = easier to arc), and to absorb less heat.
I really appreciate the responses I've had on this and I think that the durability and cost of replacing the copper more often has convinced me that the iridium will be more cost effective in the long run.
I am driving almost 2 hours a day for my commute (about 70 miles). That would mean I would be replacing copper plugs every 285 days if I replace them every 20k like I have seen people recommend vs 1428 days with the iridium ones lasting for 100k. Thanks to everyone
If any thing they reduce economy. Copper is the best conductor. I doubt you would see any difference between standard copper and iridium though, besides a longer life of the plug. I prefer standard plugs. And change every 30k.
