OK Guys and Girls,

This question is so basic I hope it doesn't stir up toomuch laughter when you read this. I just checked the air pressure in all 4 of my tires.. I have a COLD reading on the left side both front and rear of 30 and 29 which is perfect, however the right side is around 26 and 24, so I'll be off to get some air in the morning. I read somewhere that their can be a difference between COLD andWARM readings of 6 to 8 pounds,Warm being higher.... Now when I go into one of those air pumps and let's say I wanna put some air in the right side which is low, OK I set the Air pressure at 30 or 29 depending on front or rear that I want to add to.... Now since the tires are warm will I even be adding any since the reading would be Higher since the tires are warm and reading higher than the cold setting... I hope my question makes sense and I have no clue how those air pumps at the stations work. Sorry for such a basic question, but This is how one learns !! Thanks for any input !!

 

Sure there is a difference between the cold and warm pressures [selling point for nitrogen intires]
when you get to the air pump to add air, the air from the compressor will be cold, and also as it is expanding going into the tire, it has a cooling effect as do most expanding gases.
So to I guess toanswer the question, I would setthe pressure to your normal 'cold' temp.

just for grins and giggles you could check the other tires you aren't going to add air to.

 

Thanks Hondadude... At least you didn't laugh !!

 

I did HA HA! No just kidding! I would agree with dude.

 

Nitrogen does the same thing.

Actually, you can add air, maybe a little extra, then measure tire pressures (& adjust)tommorow morning when they're cold.

 

I think the nitrogen thing is b.s.

N2 and O2 are both gases similiar in size and aren't polar. The expansion (then cooling) of gases is a property gases, and not based on the elements in the gas.

 

also nitrogen heats up faster than oxygen do if you screw up and put too much N2 in a tire then theres the possibility of the tire exploding when it gets too hot.

 

I'm skeptical... Why is that?
Compared to air, nitrogen (@30psig)has 0.26% larger density, 0.26% smaller heat capacity.

 

In any case, your wallet gets emptied 100% faster if you pay someone to put nitrogen in the tires. Besides, isn't our atmosphere most ly nitrogen anyway? I used to work at a dealership, and there was always some maint. service to push on unsuspectingconsumers. Dealership service departments don't likeservice writers who know how to keep cars running properly. They want people who can sell you nitrogenfor your tires.
I'm not saying there's zero benefit....just that you'd be better offspending the money ona good tire guage to keep in the glovebox. For keeping tabs on the old fashioned air in the tires.

In reference to the warm tires, we used to just add a couple of pounds to the recommended spec when servicing hot vehicles. That got it pretty close when everything cooled off.

 

you just answered your own question, larger density and smaller heat capacity means that when the gas itself heats and expands theres less room for expansion due to the larger molecule size. therefore it heats up to a certain point and theres no more room in the closed expansion of the tire then it pops.