My '04 had Michelins and my '06 has Pirellis. It feels as though the Pirellis help the vehicle ride a bit smoother and as far as traction goes it's too soon to tell on the Pirellis - but my Michelins did great in rain, dry and snow (4+" deep).

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MWBBMW
2006 X3 3.0i Highland Green Metallic, Sand Beige Montana Leather, Steptronic, Premium Pkg, Cold Weather Package, Privacy Glass, Xenon Headlights
2007 328i 6-speed, Black Sapphire Metallic, Sport package, Black Leatherette, Heated Seats, iPod & USB Adapter
If God had intended man to walk or fly, he would not have made BMWs!