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.

Are you the one who set the tire pressure before the low pressure signal?

I have found that my dealer uses 35 psi, and my tire shop does the same.

I talked with our local tire place, and was told that the tire pressure sensors are triggered by any drop of 10% air pressure from the set pressure. So, if there's 30 pounds in the tire, 27 pounds of pressure will set off the sensor.

I guess I should be grateful; it sent up the low pressure flag again today, and the right rear was, again, down to 27 pounds. Going into the tire shop Monday to see if there's a nail...

Back in the 'good old days' when radial tires first came out, people used to tell me my tires were flat because they didn't look like round donut bias ply tires.

Yes, I agree with you, that 3 pound difference is quite minuscule. But a low profile tire doesn't have that much air volume to play around with. Volvo, and other car makers are just playing it safe. Thank goodness the new cars finally show the actual pressure on the dash, like Canada has done for years.

The low profile tires look great, but I don't like them. They ride too hard, they wear out too fast, they heat up too fast, and they don't have enough air. And, they like to have you keep the air pressure consistent, even when the temperature drops 40F.

I just had to add air to my daughter's Outback, one of the tires was getting low. I drove 1 mile to the service station, pumped all 4 tires up to 36psi knowing that a cold front was on its way. I checked the pressure 2 days later and it was 31psi on all 4. And these are not low profile!

Find yourself some used rims, put nice tires on them, and 'save' the low profile for summer use only. Interesting, I just checked Tire Rack and they list 16" wheels: 225/60/16. I wonder if they fit over the caliper, and if they do, it would be much better for a commuter car, especially snow tires.
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Keeping it running is better than buying new

Our big objection to them is that the sidewalls fracture if you hit a pothole or run over anything thicker than a flattened squirrel. If I'd known that we'd have these issues when we bought the car, I'd have bargained with the dealer for higher-profile tires!