I'm up in absurdly cold VT right now, where the temp is -1. When I went to my 2008 A4 this evening, the tire inflation sensor told me that my tires were underinflated. I went to the gas station and inflated the tires (they were, indeed, down to about 20 psi).

Questions: should I listen to the sensor in weather this cold; when I get somewhere it's warmer should I let some air out of the tires; and is it normal for the OEM tires on an A4 to lose pressure in 0 deg. F temps?

FiveG

 

You remember back in high school physics, you learned about the ideal gas law - PV=nRT, where the P is Pressure and the T is temperature?, so as the temperature goes down, with the volume (V) constant (the air inside your tire), so does pressure.

Yes, you will need to let some air out when the weather warms up or you will be over inflated.

See http://en.wikipedia.org/wiki/Ideal_gas_law for more details

 

I disregard that gauge in the winter here in Colorado Springs... Drive it for 20 minutes it will turn off as the air in your tires warms up a little.

Nothing to sweat over. Plus, a little under-inflation can be good for traction when roads are slick (μ = F/N)

 

Just curious, how much should the tire pressure go down for the
indicator to show a problem(with the expected being around 35 psi)?

The reason I ask is, I got a nail kinda thing in my front right tire last
year. Not a flat tire situation, but I was losing air steadily. I noticed it
when it was around 17 psi(felt rough) and had it fixed. But the
indicator didn't turn on anytime during this episode

2007 A4 Quattro

 

Sorry I just rembered, it was somewhere between 22 - 25 psi when
I noticed the problem(not 17).

 

nlnfns.....im not 100% sure but i don;t think all tpms systems are the same i had an xterra a big ol SUV and if i dropped or raised 3 psi it would go off so it was very sensitive my only thoughts is that with suvs its more sensitive then sedans because the risk of under inflated tires is more serious then with sedans but idk