My 2010 Mustang GT was delivered with 40 psi in the front tires, but the decal says it should be 32 psi. Any idea why it would be higher than the decal? Should I leave it alone, or let some air out?

 

Let some air out.
Don't run any higher than 35, IMO.
Anyone can put air in your tires before delivery.

 

Tire pressures and temperature:
http://www.tirerack.com/tires/tirete....jsp?techid=73

Tire pressures and altitude:
http://www.tirerack.com/tires/tirete...jsp?techid=167

Not that I'm saying any of that happened, and most probably not all at once, but an 8 PSI swing isn't out of the question.

This is why you always measure your tire pressures *cold*. It's a more accurate reading than during the day or while driving and also more consistent, as you're always doing it at the same time... right?

 

Thanks for the good info! That's what I thought, but I've been wrong before. They measured 40 psi on a brand new dial gauge while they were cold...hadn't been driven in 48+ hours. I'll adjust it back to the recommended pressure first thing in the morning (unless someone comes up with a good argument between now and then).

 

Just thought of one more thing... if their gauge, or yours, is out of calibration, that can explain the problem as well. In fact, most gauges you see sold have an accuracy that's +/- 2 PSI, or more(!). So get a good one, or maybe get three and average them out or take out the weird one.

 

Definitely let some air out. Go with what it says on the sticker.

 

Anothe point to consider, increasing the air pressure also changes the way the sidewall reacts (like changing the damper or spring rates) and has an effect on the contact patch.

 

I checked it against another gauge, the difference in readings was...about 2 psi! Rear tires have read 32 psi all along. So I don't think it was a gauge problem. All 4 tires now have the same pressure anyway. I'll get it to a tire shop soon and verify my gauge just to be sure. Thanks again!