Putting heated air in a cold tire

[Paintedcow]

I keep my air compressor in the house or it wont start or the line freezes. To pump up a tire, I have up to 165ft of air hose. Normally my

50ft and 15ft coupled together will reach my truck or tractor.

Anyhow, the air coming from the house is warm, (60 to 70 deg F). When the outdoor temperature is zero or colder (F), that heated air is going to change in pressure when it gets cold. I cant determine if the tire will gain or lose pressure when the air gets cold. I'm sure it's not a significant amount, but I'd like to compensate when I put the air in the tire.

But which way, up or down?

[DerbyDad03]

Figure it out based in the info found here:

[DerbyDad03]

More info here:

[trader_4]

Air coming out of an air compressor is going to be colder than ambient anyway. It gets compressed, loses heat, which is why compressors get hot, then gets expanded again getting colder when it exits the compressor system at a lower pressure.

All in all, I wouldn't worry about it. Nobody else does and the effect isn't large. The air going in the tire probably winds up close to the temp of the tire quickly anyway, especially if you're only topping it off.

[Stormin Mormon]

Cooling air lowers the pressure. You'd want to over inflate the tire warm, so it's close to correct when it cools.

[philo]

On 01/29/2016 07:15 AM, trader_4 wrote: X

then gets expanded again getting colder

Totally nothing to worry about. after all once the car is driven the tire is going to warm up considerably

[Stormin Mormon]

How much do tractor tires warm up, when travelling at 5 MPH? Considerably?

[EXT]

Running the compressed air through the outdoor portion of the hose will cool the air before it gets to the tire.

[Tony Hwang]

Line freezes? Water! No pressure gauge? Worrying way over too much!

[Stormin Mormon]

I think it's fun to consider such trivia, now and again. Oh, I'm going to use the N word!

Nitrogen!

[Ed Pawlowski]

A couple of weeks back we had a discussion about tire pressure. Since that time I'd watched mine to see what happens. The start of this was when my TPMS went off on a very cold morning as one tire was down to 24 psi. Many newer cars give actual reading by tire. That afternoon after a 25 mile drive back home I inflated them all to 34psi by my gauge, but the readings from the TPMS showed the rear tires 1 psi higher.

Observation over a couple of weeks shows be the following: Starting out at 25 degrees FL 31 31 RL32 32 Driving 2 miles FL 33 33 RL34 34 Driving 25 miles FL 34 34 RL35 36

As you can see the right rear tire reads 2 psi over the front tires. They increase at close to the same rate, but not exact. I have no idea exactly what the pressure is due to rounding and normal tolerance for the sending units.

Tire inspection during an oil change last Saturday showed all tires are wearing evenly at 7500 miles.

Conclusion: Close enough for me. Too cold out to worry about a half pound difference in pressure.

If I had your situation I'd inflate to 2 or 3 psi above the recommended pressure and not worry about it.

[Micky]

I hooked up TPMS to my front tires. By the time I had reached the corner, I found the air tubing wrapped 85 times around the axle.

Sounds good to me.

I got longer tubing, so now I can fix my TPMS.

[bob_villain]

I can't help but think Micky and the Mormon would be involved in this outcome.

[21blackswan]

put [much] more than you think it will need,

and take the excess out later

marc

[MLD]

Running the compressed air through the outdoor portion of the hose will cool the air before it gets to the tire.

Without going through the arithmetic --A safe estimate would be to use the following as a pretty good guide: For every 10 deg change in air temperature the tire pressure will change 1 psi. Pressure increases as the temperature goes up and decreases as it drops. This assumes starting with a tire at ambient air temperature (not a flat) and not worrying about the temperature of the air going in since its volume is relatively small. Ref: Ideal Gas Law MLD

[Ed Pawlowski]

One thing we did not consider is the volume of air added. If the pressure is only raised a couple of pounds it will be insignificant comared to filling a tire with np pressure.

[Tony Hwang]

I always check tire pressures once a month. Just can't depend on TPMS alone.

[gregz]

Depends if tire is in the sunshine. I always have to compensate one side vs other if car is in the sun. Can be several degrees.

Greg

[thekmanrocks]

Painted... wrote: "Anyhow, the air coming from the house is warm, (60 to 70 deg F). When "

Oh SHEHEEZZZZ.. And I thought we were talk the temperature of exhaust out the tail end of a F-18 fighter plane here!

Just put in a couple psi more than the recommended pressure on the b-pillar door placard. No big deal, said Katy!

[Dean Hoffman]

The 5 mph sounds slow for field speed nowadays. U.S. tractors generally top out at around 25 mph road speed. There are laws governing top speed for vehicles with the Slow Moving Vehicle signs. Rear tractor tires also have calcium added for weight and traction. This article

makes it sound like Fastrac is making a model for the U.S. that can run up to 50 mph. That would make life interesting with a ten year old running it.