Tire pressures during temperature swings

[DarkSkySeeker]

I see a 3-4 PSI rise in my Ram 2500 tires from a cold start to highway driving after 30 minutes.

During the day, if starting off from a cold location, to the hottest destination, do you account for the warmup and adjust your pressures to compensate?

I figure from a freezing location to a hot desert destination, I could see a 70F air temp swing, and wonder if I should bleed pressure as the tires get warmer and warmer.

[spoon059]

Why do some people feel the need to over engineer things? Your tire pressure tables are COLD pressures. Cold is defined as tire at rest, not having recently been driven. Whether cold is 0 degrees or 100 degrees, cold is cold.

Before you start your day, check your COLD tire pressure. Set your tire pressure to the recommended PSI. Drive. If you feel the need to check pressures during the day, simply ensure that the PSI hasn't dropped from your initial COLD pressure.

Its tire pressure people... some things are meant to be simple.

[DarkSkySeeker]

RCMAN46 wrote:


How did you determine that the tire temperature had increased 3-4 degrees?

Drilled a hole in the sidewall and quickly measured it with a thermometer before the air ran out :S

Of course, I should have written PSI.

[RCMAN46]

DarkSkySeeker wrote:
I see a 3-4 degree rise in my Ram 2500 tires from a cold start to highway driving after 30 minutes.

During the day, if starting off from a cold location, to the hottest destination, do you account for the warmup and adjust your pressures to compensate?

I figure from a freezing location to a hot desert destination, I could see a 70F air temp swing, and wonder if I should bleed pressure as the tires get warmer and warmer.

How did you determine that the tire temperature had increased 3-4 degrees?

[Lwiddis]

Set the tire pressure when they are "cold"...undriven...and leave them alone.

[ktmrfs]

GordonThree wrote:
So no problems if I set the cold pressure at 15F ambient and later in the day it's 50F ambient? Often see huge swings like that around spring.

while 35F may seem like a big temp swing, it really isn't relative to pressure changes. First convert to Centigrade. it's a 20C delta.

Next, boyles law states PV=rT. tire volume remains the same, r doesn't change, so pressure is related to temperature change in a linear fashion, but 15F is about 260 degrees Kelvin, so we are looking at a 20 degree change relative to 260Kelvin. about a 5% change in pressure. so given say a 60psi at 15F changes to maybe 63pis at 50F. not enough to normally worry about.

Now what can also have a noticeable effect on pressure is how much water is in the air in the tire. as water heats up and vaporizes, it increases tire pressure as well.

Now if it's a racing situation, another story for caring about PSI changes. That's why most racing teams use dry nitrogen. They don't need to worry about pressure changes due to water vapor changes and they have a known defined characterized gas.

But in the end, for us travelers, check and adjust your pressure with the tires cold and don't worry about it during the day. Tire mfg have already accounted for temp rise effects in the tire design.

[ksg5000]

Sometimes common sense takes precedence over the internet. Anybody really believe that tire makers didn't know that weather changes when they designed their tires? People don't adjust their tire pressures daily/hourly or whatever based on weather. End of story.

[Sam_Spade]

donn0128 wrote:
I checked my tires at the start of the season and left them alone.

If that means that you don't check the pressures again during the season, you are playing with fire and it will burn your butt eventually.

[GordonThree]

So no problems if I set the cold pressure at 15F ambient and later in the day it's 50F ambient? Often see huge swings like that around spring.

[donn0128]

This is all silly nonsense. Unless you have a leak a tire will only loose 1-2 pounds in six months. I checked my tires at the start of the season and leave them alone. Heck, you can loose 2 PSI every time you check them.

[drsteve]

phillyg wrote:
According to every tire mfgrs. info, you set pressure when the tires are cold, i.e., not having been driven on, and leave it alone.

What he said^^^^^^

Tires are engineered to be driven on without constant air pressure adjustments. Set the cold pressure, hit the road, don't worry about it.

[DarkSkySeeker]

I like the statement, "don't overthink it".

And, I'd expect the pressures the next day to be nearly what they were the day before.

I've seen 8-10+ PSI increases from the coldest starts to the hottest running, and I have to admit (despite the references to tire mfg-ers statements) that it concerned me.

One time, I stopped on the side of the highway and bled 4 PSI of pressure.

[Vette_Racer]

I set mine at 122 in the morning and usually see temps in the 145-150 range but once going from high altitude and cold temps to lower and hot temps tires went from 122 to 165 according to TPMS.

[MFL]

I never bleed air from morning start, while driving to destination. I will wait until next morning, at new location, to adjust.

Yes, a 70 degree difference in temp will make a noticeable difference. While this is not the norm, in this case I might consider starting pressure a lb or two less, while days end will likely be over pressure. In any case, tires are designed to inflate when heated, but tire makers still say "go by cold pressure, before travel."

Jerry

[SidecarFlip]

Interesting subject. I had my TPS come on, on my car the other day. I know none of my tires leak and I usually check and air them every 3 months but it's been cold here and my tire pressure had dropped below the TPS threshold. I aired them back up and all is good.

I don't believe 3-4 pounds means squat. I always run my TP at the maximum sidewall rated pressure. I get better fuel mileage that way.

[phillyg]

According to every tire mfgrs. info, you set pressure when the tires are cold, i.e., not having been driven on, and leave it alone.