I bought a certified pre owned SLK 350 in August of 2014, it had new tires on it and had just been aligned. Since then, i have replaced the rear tires 3 times and 1 new alignment. 2 sets of Pirelli and one set of Michelins. I have 18 inch wheels. I have put 16K miles on the car in a little over 2 years, and i now need to put a 4th set of rears on ! Fronts are fine. I am 69 years old, i don't drive it hard. Is 5K/set "normal" wear. How many miles are others getting on rear tires ? Other than alignment, what else can be done ?