Our 2008 S80 turned on the "low tire pressure" sign today while my wife was ten miles away. She checked, and there was no obviously flat tire, so she limped home. When I checked, the tires on the left side were at 30 pounds; right front was at 28 pounds; right rear was at 27 pounds.

Are the tire pressure sensors normally that sensitive? Or should I be asking the question, do low profile* tires need perfect pressure at all times?
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*That should be d--- low profile tires. We've spent more on tires since we got that car four years ago, a car on which we put only about 5,000 miles/year, than we've previously spent on all our cars combined in a decade.