I'm going to wait to replace mine till around 80-100k, probably closer to 80K. My mechanic, along with the dealership mechanics, say that spark plugs and wires should be replaced around 100k. I bought the car used with about 53K on it, and I have no idea how the original buyer drove the car, where it was driven or under what conditions. The car was bought at a dealership as a certified used vehicle.