Running on deflated tires will result in bad tire wear, lower gas mileage, and maybe even cause a blow-out or rim damage. If you really hate the ride, sell the 19" and buy a set of 18" wheels.

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'06 X5 4.8is, TiAg/black, cold weather pkg., comfort seats
'07 750Li, TiAg/black, sport pkg.
'05 Ford F350 silver met./slate gray, Lariat, 6.0 PSD, CC, DRW, FX4