whenever its really cold outside and my car hasn't been on in a while (~10 hours) the front passenger side tire check pressure light always come on. my tire pressure is always fine tho and the light goes away after a while of driving. its just annoying. i was gonna rotate my tires to see if the problem would follow the tire but havent got a chance

 

Tires pressure changes about 1 psi for every 10 degrees temperature change.

What is the cold tire pressure as measured by a good guage (not a stick-type)?

 

Bearcat is right.. when it gets cold.. air gets dense and compresses in your tire. Look up the IDEAL GAS LAW:
So what you have is the absolute pressure is proportional to the temperature. This is called the ISOCHORIC PROCESS. The relationship is pretty simple:
which means the relating temperature change ratio is proportional to the relating pressure ratio.

so if it's 20C (68F) in the day and 0C (32F) at night that is a 20C / 20K difference. The relating ratio (in Kelvins only, which is proportional to Celsius) is 273.15 / 293.15 or 93%. You can expect your tire pressure to be as low as 93% of the starting pressure. If you had 40 psi you could expect a drop of 40 (0.93) = 37. This isn't absolute because a tire isn't perfect (non-ideal), but you will definitely notice a change in pressure with a change in temperature. But as you start driving the pressure will increase because your the heat from you tire will expand the air in your tire. This is why it's important to check your tire pressures during great changes in temperature. Your tire wont always expand to the original pressure, remember it's non-ideal.

 

I keep my winters at 32 for flexability and I get the warning once its a few degrese below freezing.

The annoying part is once its acknowledged the damn thing keeps comming back. You should be able to acknowledge it once and then it goes away or maybe just the icon on the speedo but no .. it comes back all the time and its annoying ..

And no .. I'm not increasing the tire pressure 1) I prefer the traction .. 2) And if I do then once it warms they are over inflated.

 

I don't have TPMS.. I have an '04.. sounds like a PITA / real nuisance. Well I'm sure it's good for some. I think it triggers when the tire is around 26-27 psi.. not sure though. You could disengage it.

 

Engineer like myself?? was going to post the exact same comments.

Anyways, once you are on the road for a bit, friction heats up the air in your tires a bit which will increase their pressure.

Are you filling your tires to ~34-36 psi after you have been driving on them for a bit or when they are cold?

 

Yeah.. EE.. I see you're ME.. we can talk shop nice S2k.. I hear they may end production

 

Wouldn't having the tires filled with nitrogen help? Seems like I remember reading that nitrogen doesn't expand/contract like air...just a thought

 

air is typically ~70% nitrogen. Nitrogen doesn't compress as much as oxygen so it would help, but I'm not going to pay $5/ tire to get it filled with nitrogen. .. nitrogen fills are good for some but definitely unnecessary for most.

 

Thanks, yes 2009 is the last production year, we're supposedly getting a special edition, but its just aesthetics.

As for nitrogren filling, it only decreases the diffusion/leakage rate through the pores in the tire or any of the less than perfect seals you may have between the rim and tire. it also give you dry air (0% humidity) which allows for less pressure change due to temperature changes.

Atmospheric air (what you fill your tires with when you use a common air pump) is about 78% nitrogen on average so really the only benefit youd get is less pressure change. Not worth it IMO since I can just get free air at the gas station down the road anytime I want.

 

thanks guys for the replies. i checked all my tire pressures and theyre all pretty much the same. maybe the sensor is acting up? i will rotate the tires when i get a chance and see if it follows

 

If the sensor is reading more than 3 psi off from a KNOWN accurate gauge than the sensor is NG.

 

OK, what psi are you running up front?
The reason I ask is that a lot of people run 30 psi, measured cold, up front-- which is too low. When the temp drops 40*F, your TPMS warning will activate because the TPMS is detecting 27 psi or lower.

Try inflating to 33 or 35 psi up front while the tires are cold.