andrewwynn, I don't have the experience with oil on the road, but a few decades ago when I couldn't afford another set of tires I was forced to drive my winter tires through the summer. I know exactly what you're talking about with the increased grip but I seem to recall the wear rate on my Hakkas was concerning enough that I only got 2 years out of them IIRC. That was on my 86 Volvo wagon. Not even a beast like the X5. BUT I was commuting 2 hours each day.

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2005 Titanium Silver X5 4.8is (DD winter) * 2001 Steel Blue 750iL (DD summer) * 2001 Ford Excursion 7.3 L <> 2005 X5 3.0 * 2003 X5 4.4i * 2009 X3 3.0 * 2009 X5 3.0 * 2007 Toyota Avalon Limited