I have about 20,500 miles on my two year old Model S, 90D, original tires, and was told that I'm in need of new tires pretty soon. I am not a hot-rodder and drive fairly conservatively, so I was surprised that my tire life is so low--only have about 3mm of tire tread on all my tires (I've had them rotated regularly). Is my experience quite normal? What have other Model S owners encountered? Also, what kind of replacement tires do others recommend?