I'm running with the standard 19" on my new P85D. Traction has been great, but I've found that the snowy weather really wreaks havoc with some of the autopilot features. The lane departure warning frequently goes off due to snow on the road even if I'm clearly in the middle of a lane. The parking sensors can easily get snow on or near them which causes them to blare the red stop warning whenever I am coming to a stop or starting to move again. Unfortunately, there doesn't appear to be any option to turn this alert off or silence it. The cruise control will intermittently stop working. Sometimes for minutes, sometimes for half an hour or so. When I try to engage it, it just says "Cruise not available". I've reported this problem to support as it might be an actual technical issue rather than just inclement weather. I've had the collision warning go off a couple of times when there was no clear danger. Both times, there were snow banks near by, with either my car or a car in front of me in the process of turning. I suspect it got confused by the snow bank and thought the car was closer or in a different position.