Air Up Hot Tires

[Nostrathomas]

Could not find anything in the archives.

On a recent trip, we aired down to 15 PSI. At the end of the trip, we stopped to air up and thought we were good to go. The next morning all tires were about 10PSI low.

Any guidance on getting closer before the trip home with hot tires?

 

[Dimhof]

I've been running into this problem lately since Wheeling more in Southern Utah, although ive been 5psi low in the mornings at most. I doubt there is a way around this unless you are throwing 'room temp' or colder air into them from a tank in the cab. I imagine the temp of tires and temp of air being used also contributes to this. I am not with a dual ARB under the hood. I have tried to throw in around 5psi more when airing back up although I always check all 4 tires the morning after anyways.

 

[03_4x4Runner]

Check your tire psi sometime after a long drive when they are hot and compare that to the cold temp. That will tell you the psi change. If you air up immediately after you get off the trail fill the tire to the normal psi hot pressure and you will be close.

 

[greatape]

It's normal just trend and analysis it as said...

 

[4OYOTER]

I work in the tire industry. We are taught to air up hot tires +4 psi over what the desired cold psi is. YMMV. Especially if going on long road trips where the ambient temperature is going to change from location to location, but this should be a good starting point. Nitrogen would help with your issue, but if you are airing down on a regular basis it will be almost pointless, as you will then probably have to air back up with regular air.

 

[Jeremy556]

Check air pressure when you are about to air down, air up to the same pressure. After a while, you'll know the correct pressures based on ambient temp and how hot you are getting them when aired down.

Temperature of the air going in doesn't matter, it is the tire carcass which holds/retains the heat.

 

[Dimhof]

Check air pressure when you are about to air down, air up to the same pressure. After a while, you'll know the correct pressures based on ambient temp and how hot you are getting them when aired down.

Temperature of the air going in doesn't matter, it is the tire carcass which holds/retains the heat.

So throwing air in from an arb compressor when it is 100°+ outside will not contribute to the air condensing over night in cooler temps and a lower psi reading? Do the tires really get that hot to skew psi readings instantly?

 

[wcjeep]

When towing I have found the sun side of the truck has tires that are 10deg warmer. The air pressure can also vary with temp and elevation.

 

[DesertCanyons]

Hot tire air pressure

PV=nRT is an old, tried and true, basic physics relationship. Pressure varies directly with temperature. Translated, it means pressure times volume equals number of molecules n times a gas constant R times Temperature T. V and R are fixed - the tire volume doesn't change much near the range of ideal pressure. You can add more air, the n factor. You can vary pressure by adding or removing air. Temperature changes happen beyond your control. As temps rise the pressure rises and vice versa. If pressure drops as temps drop, add more air until you get the desired pressure for your tire.

And yes, a hot tire that weighs up to 55 pounds will heat all the air you can put in it in a hurry. The air weighs next to nothing.

The pressure ratings for your tire are printed on the sidewall and it refers to the pressure when cold. Expect the temp of the tire to rise when you're driving.

 

[MSRP.]

Just echoing what the previous poster said regarding giving it a few more psi's than ideal when airing up after the trail. If you wanted to save time the next morning, and were willing to sacrifice the relatively poorer ride quality (harshness), 5 extra psi's won't be a huge difference.

I would also recommend double checking your tire pressure gauge with another gauge just to make sure it is reading accurately/consistently. 10psi drop from parking to the next morning, is quite a large drop in the northern climate, not much experience in the hotter deserts.

 

[BobsTrail]

:iagree:

I usually run 34 psi in my Toyo AT2's. When I air up with my CO2 I go to 38. When I check it the next morning it's usually at or close to 34, but I always check. Not sure how the cold CO2 compares to hot air from a compressor, but this works for me.