Tire pressure

[37chief]

I checked the pressure in a tire this morning Temp was probably around 32. Pressure was down from predvious day by 8-10 lbs. About mid day it was back up the same amount. So if I want 80 lbs in my tires, is the pressure going to increase a lot when the tires hit the road. Should I just put in 80 lbs in at mid day and not worry about it? Stan
 

[oleblu]

Stan

Set your tire pressure at 80 with the tires "cold", meaning not driven more than a mile or so. The pressure will increase slightly when driven, maybe 4-5 pounds. That"s the way it should be done.
When the outside air temp goes back up (lets say to 60 or 70 degrees) then you need to check your pressure and adjust acordingly. Air pressure should be checked monthly.
 

[504]

Check tire PSI cold. If you are going on a trip fill cold and if you check them hot you are just making sure they are the same, if three are 90psi and another is 75 psi you know the low tire needs attention.
 

[flying belgian]

Stan. Are you saying the pressure changed by 8-10lbs. with out even driving it? Went down first and then back up? Only thing changed was the time of day? You gotta get a new tire gauge. That's where your problem is.
 

[37chief]

The tire guage is top of the line, no china crap. Tire was very cold in the morning, and hot in the afternoon. I will check again in the morning, as I know the exact pressure now. Stan
 

[Hay_Man]

Also will change like that as Low Pressure weather areas pass your area and high pressure builds back in. What you see on your tire gauge is a pressure differential between the air in your tire and the outside air pressure.
 

[Hay_Man]

Also as the air in the tire heats up, the pressure will go up. You have to anticipate the heat build-up as you drive down the road. That's why the tire's rated pressure is "cold". If you have too much pressure it the tire when cold, it will probably build up too much pressure as it heats up while going down the road and blow out.
 

[John B.]

Be sure to check the air pressure in your spare tire too Stan! The spare is out of sight out of mind usually.
 

[Wayne in MN]

10 degree temp change will cause about a 1 PSI change in tire pressure.
That is why us "northerners" put winter air (denser) in our tires each fall & summer air (not as dense) in come springtime. :>)
 

[jon f mn]

Air pressure on my truck tires only varies 1 or 2 pounds usually. They always drop slowly, but rarely gain more than a pound or two no matter how hot they get. I can count on about 5 lbs drop per month in my truck tires, a little more in the winter. I also would say try another pressure gauge. Heres a link to a test.
Untitled URL Link

 

[dpendzic]

you could compute it using the universal gas law---PV=NRT if you know the volume of your tire.
 

[showcrop]

It is not all that unusual for an inexperienced tractor pulling competitor to get disqualified because of setting his hitch height early in the morning, and then those big tires sit in the hot sun for a couple hours and they grow.
 

[Hay_Man]

I run tires with heavy loads on them, so they get hot and the air inside them gets hot and expands, causing high pressures. I have noticed with the quality of tires going down these days, air will leak out easier. The air molecules are able to leak out past the tire plies with the heat and higher pressures. The heat deteriorates the tire material and the air is able to escape more and more. Nitrogen has larger molecules which stay in the tire better under pressure. But I don't use Nitrogen in my truck tires. I have noticed I have to add air more to the low-profile tires on the cars nowadays. They just don't hold enough volume of air to maintain pressure for very long. I guess that's why some shops put Nitrogen in those little tires. I think Green Slime helps seal the tires against heat deterioration and thus helps to maintain air pressure, but sure screws up those in-tire pressure sensors.
 

[DiyDave]

You need to change out all that summer air, and replace it with winter air, it's more dense, and less humid, so pressure stays more the same. If you live near a dairy, don't put in no dairy air...
 

[Fred from MO]

Now that was funny!!