So I today I pulled the spark plugs from my Mazda at just over 50k miles. Here is #1 And #3 The electrode on the no 1 plug is a little worn, while the no 3 looks fine. I did not look at the rest of the plugs, but what would be the cause of the tip wear? The car runs just fine and I was planning on keeping these until 75K, thats when the manual recommends changing them, I gues if they lasted 50k another 25 should not be a problem. What do you guys think?