I really enjoyed my Michelin X-Ice tires but found they wore out quicker than expected. I suspect the same formulation that makes them perform well in the cold and ice makes them wear more quickly in dry, warm conditions...especially with heavier vehicles.

I'm finding that my Pirelli Scorpion Ice/snow tires are holding up better over time with similar performance in snow, ice and better performance in the dry.

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2005 X5 4.4 (Sterling on Truffle) w/sport everything
2011 Audi S4 (Prestige, DSG)
2012 Audi Q7 (Sport, S-Line)