Tires: tire pressure on low profile tires, low profile tires, pressure gauge

Question
I have a 2010 Kia Soul with pirelli low profile tires. The maximum pressure displayed on the tires is 40 psi. When my tire pressure dash light turned on I got out my compresser, set it for 40 psi, and it automatically cut off as soon as I turned it on. I got the same result on all four tires. I assumed this meant all four tires were maxed out at 40 psi. None of the tires appeared low on pressure either.  I took it to Kia and they told me the pressure on all the tires read 20 psi so they aired them up to 32 psi. Now my question.... I've since purchased a decent pressure gauge, and while cold, my tires are reading 45 psi. I double checked the gauge against a friend's tires which read 30 psi.  The gauge seems totally accurate.  If Kia set the tires at 32 psi, then why would they be reading at 45 psi? Is there something I don't know regarding low profile tires and their pressure?  

Answer
Martin,

Pressure is pressure, but not all gauges accurately measure pressure.

Plus, you need to be aware that temperature has an affect on tire pressure.  Low temps --->  Low pressure.  So if you set your tire's pressure on a warm day, the pressure will be lower when it is colder.