I have a 97 e320 w/ same Michelin MXV4 tires. I have about 38k and I still have considerable tread left. Probably, you are accelerating to aggressivlely. Like me you probably have ETS and it disengages after 25 MPH thus you could still be squeling your tires, unnecesarily. Keep your foot of the gas and you will be enjoy longer tread life.