Setting proper tire pressure

[azbigfoot]

Alright its early morning with brisk 40 degree temperatures. The sun is just rising and we're preparing to move on to the next campground. Part of my usual list is checking the tire pressure. So I've wondered ... what should my tire pressure read? I know at 70 degrees it should be 110 PSI.

I've heard the rule of thumb is about 2% PSI per 10 degrees. So 2.2 PSI per 10 degrees means 103 to 104 PSI would be a good reading at 40 degrees?

This seems to hold also for driving conditions. The tire temperature is roughly 130 degrees when driving. That would be a 60 degree shift and I would see about 12 or 13 PSI increase. My Valor TPMS usually reads in the 120-125 PSI during normal driving.

Is this what others see? How do you handle pressure checks at different temperatures?

 

[branson4020]

I handle it by ignoring the temperature and inflating to sidewall max pressure always. I suppose if I was in sub-zero temps I might do something different.

 

[Garypowell]

Unlike Branson4020 I am very particular about my pressures. He might be right that there is plenty of margin for error....but after two blow outs (now blow out free for 2+ years) it is working for me.

I have a Valor TPMS system so I know what the inside temperature is but if you do not I'd be careful about sunlight on those black tires. I see a great difference in pressure when first starting out from sunny side to dark side.

But I use the rule of thumb you quote above....I have heard it here and seen it on the web on tire sites.

I have only started out in cold temps like you report a couple of time and it is scary to leave the pressure that low....but once heated up they look like normal pressures so it seems the rule of thumb works.

 

[danemayer]

Alright its early morning with brisk 40 degree temperatures. The sun is just rising and we're preparing to move on to the next campground. Part of my usual list is checking the tire pressure. So I've wondered ... what should my tire pressure read? I know at 70 degrees it should be 110 PSI.

I've heard the rule of thumb is about 2% PSI per 10 degrees. So 2.2 PSI per 10 degrees means 103 to 104 PSI would be a good reading at 40 degrees?

This seems to hold also for driving conditions. The tire temperature is roughly 130 degrees when driving. That would be a 60 degree shift and I would see about 12 or 13 PSI increase. My Valor TPMS usually reads in the 120-125 PSI during normal driving.

Is this what others see? How do you handle pressure checks at different temperatures?

We left Breckenridge one February morning at -2F. I think the TPMS was showing pressure at about 98.

 

[tireman9]

Alright its early morning with brisk 40 degree temperatures. The sun is just rising and we're preparing to move on to the next campground. Part of my usual list is checking the tire pressure. So I've wondered ... what should my tire pressure read? I know at 70 degrees it should be 110 PSI.

I've heard the rule of thumb is about 2% PSI per 10 degrees. So 2.2 PSI per 10 degrees means 103 to 104 PSI would be a good reading at 40 degrees?

This seems to hold also for driving conditions. The tire temperature is roughly 130 degrees when driving. That would be a 60 degree shift and I would see about 12 or 13 PSI increase. My Valor TPMS usually reads in the 120-125 PSI during normal driving.

Is this what others see? How do you handle pressure checks at different temperatures?

Am I correct in assuming from your mention of 70F that you have been told to adjust the inflation to a "Laboratory Standard" of 70F ?
This is incorrect information. Tire pressure should be set at prevailing ambient temperature.

Now having said that if there has been an extreme change in temperatures of say 50 degree drop overnight I would expect to see the tire pressure to have dropped by about 10%.

Lets assume that you have confirmed that none of your tires are overloaded and in fact you have a safety margin of at least 10% on the heaviest loaded individual tire. (you do know that axle to axle and side to side variation of 5% each is not unusual so that is why you need to get the actual load on each individual tire to confirm no overload.

Since we are talking multi axle trailers then the proper "cold" i.e. at Ambient temp tire pressure is the pressure shown on the tire sidewall associated with the max load.
I have numerous posts on my blog just on the "WHY" trailers need to run a high pressure.

Pressure checks should be done when the tires are not heated from having been run in the prior couple of hours or in the Sun for the prior couple of hours.
Tires can tolerate the pressure increase seen from normal operating conditions (no overload or high speed)

 

[Jim.Allison]

Install TPMS, and dont worry about it. Adjust pressure as needed for barometric pressure and temperature. A TPMS will show you a lot about your tire temps and pressures.

Do not adjust to Standard Temperature and Pressure. The tire manufacturer assumes that you measure the tire pressure at the existing barometric pressure and the temperature BEFORE the tires roll. They understand that if the ambient temperature is 80 degrees and you inflate to 80 that the tire will take on heat from internal friction friction and the road surface. What they can't anticipate is if one side of your vehicle is in the shade and the other side is in the sun. In this situation you must do some "interpolation." If you have no reason to believe that you have a leaking tire and you take a readings in the shade and you get a 79 on each tire in the shade and then on the sunny side you get 81 on those, then you can reasonably expect that your tires are inflated correctly and proceed without adjustment.

A practical scenario would be leaving Canada in January. You have your tires inflated to 80 psi. You leave heading toward Phoenix AZ. Here it is wise to check you cold tire pressures each departure day as you change altitudes and average daily temperatures.

If you were to be traveling in 80 degree weather on properly inflated tires and then got sacked by a cold front with sleet and snow, you would need to be sure you were inflated to at least proper cold tire inflation without regard to whether or not you have been traveling on them.

 

[JohnD]

Install TPMS, and dont worry about it. Adjust pressure as needed for barometric pressure and temperature. A TPMS will show you a lot about your tire temps and pressures.

Do not adjust to Standard Temperature and Pressure. The tire manufacturer assumes that you measure the tire pressure at the existing barometric pressure and the temperature BEFORE the tires roll. They understand that if the ambient temperature is 80 degrees and you inflate to 80 that the tire will take on heat from internal friction friction and the road surface. What they can't anticipate is if one side of your vehicle is in the shade and the other side is in the sun. In this situation you must do some "interpolation." If you have no reason to believe that you have a leaking tire and you take a readings in the shade and you get a 79 on each tire in the shade and then on the sunny side you get 81 on those, then you can reasonably expect that your tires are inflated correctly and proceed without adjustment.

A practical scenario would be leaving Canada in January. You have your tires inflated to 80 psi. You leave heading toward Phoenix AZ. Here it is wise to check you cold tire pressures each departure day as you change altitudes and average daily temperatures.

If you were to be traveling in 80 degree weather on properly inflated tires and then got sacked by a cold front with sleet and snow, you would need to be sure you were inflated to at least proper cold tire inflation without regard to whether or not you have been traveling on them.

In other words . . . we need to be rocket scientists to make sure we comply with the tire manufacture's specifications to make sure we don't have blow outs.

 

[Jim.Allison]

"In other words" you don't have to be a rocket scientist to inflate your tires. I cannot find anywhere any data that suggest any inflation practices that would require anyone to correct a pressure reading to 70 degrees.

All the tire manufacturers say to inflate to recommended cold tire pressure regardless of ambient temperature.

IMHO I say adjust seasonally unless entering into or out of weather extremes. Use TPMS to insure proper inflation. Simple. Oh and don't run TowMAx tires.

In other words . . . we need to be rocket scientists to make sure we comply with the tire manufacture's specifications to make sure we don't have blow outs.

 

[tireman9]

Install TPMS, and dont worry about it. Adjust pressure as needed for barometric pressure and temperature. A TPMS will show you a lot about your tire temps and pressures.

Do not adjust to Standard Temperature and Pressure. The tire manufacturer assumes that you measure the tire pressure at the existing barometric pressure and the temperature BEFORE the tires roll. They understand that if the ambient temperature is 80 degrees and you inflate to 80 that the tire will take on heat from internal friction friction and the road surface. What they can't anticipate is if one side of your vehicle is in the shade and the other side is in the sun. In this situation you must do some "interpolation." If you have no reason to believe that you have a leaking tire and you take a readings in the shade and you get a 79 on each tire in the shade and then on the sunny side you get 81 on those, then you can reasonably expect that your tires are inflated correctly and proceed without adjustment.

A practical scenario would be leaving Canada in January. You have your tires inflated to 80 psi. You leave heading toward Phoenix AZ. Here it is wise to check you cold tire pressures each departure day as you change altitudes and average daily temperatures.

If you were to be traveling in 80 degree weather on properly inflated tires and then got sacked by a cold front with sleet and snow, you would need to be sure you were inflated to at least proper cold tire inflation without regard to whether or not you have been traveling on them.

Jim good summary and spot on