What temperature is cold tire pressure based on?

[MN_Traveler]

Originally Posted by Polyian

Nice write up MN Traveler

I don't have a recommended minimum tire pressure, only the coach manufacturers recommended pressure and the tire manufacturers maximum pressure. I won't tell you what I studied or what I did for a living because it's irrelevant to the discussion. But I do know how to use Google and read information from the Tire experts.

Here is a good write up from Tire Rack:

Winter Tech Information - Air Pressure, Temperature Fluctuations

If you disagree with the tire experts feel free to write to them

Thanks Polyian. Again, sorry it was so long.

I like the article in the link you supply - I believe they are basically saying the same thing: Dont get in to a situation where the tires get colder (without running) than where you set the pressure at without checking and correcting the pressure. That is really what I meant when I said the issue is "simple".

It was the weirdest thing making that run north into much colder temperatures. I could practically not believe it when I saw the tire pressures inching down towards their minimum even though I was driving on them (and it was all of them, so likely not a "leak"). I was sweating bullets: I did not want to stop and rest for any time least the tires cool off and drop pressure more. I did NOT want to get out in sub-zero wind chill to run the compressor. Talk about pressure to keep going

BTW - all of our experiences count. I only mentioned my background to relate that I had some reason behind the point I was making. In the us the PhD degree is sometimes referred to "piled higher and deeper". In Asia I have sometimes heard it referred to as "permanent head damage". Both descriptions are sometimes all too true

[MN_Traveler]

Originally Posted by Polyian

I don't have a recommended minimum tire pressure, only the coach manufacturers recommended pressure and the tire manufacturers maximum pressure.

Oh ... I also meant to mention - maybe you have read this before, but just in case.... there are many threads on this forum regarding appropriate tire inflation. Each tire should have available a published loading curve (recommended minimum pressure versus load on the tire). You will see much discussion regarding getting "four corner weights" ... which are trying to identify the actual weight on each tire so that the appropriate inflation can be found from those published curves.

When I first got my coach, I inflated to the recommended pressure on the sidewall of the tire. The handling of the coach was ... awful. When I got my weights per tire, and adjusted the inflation per the manufacturers loading curve, handing on the unit became absolutely great.

[Polyian]

I always inflate to the coach manufacturers recommended pressure, sometimes a couple of pounds higher, never lower. I can feel the difference in front tire pressure changes and I play till I get numbers I like, write them down and stick to them....interesting topic, I don't think all owners are aware of these tire pressure facts.

[Gary RVRoamer]

The minimum psi is shown in the tire manufacturer's load inflation table for that tire model, if you care to research that (GY & Michelin publish theirs openly, but some others can be harder to find). For a motorhome, it's probably well below the recommended psi from the RV builder. For a trailer, maybe not so much.

[JFXG]

Fatchance......
The behavior of vehicle tires is the interaction of the behavior of air and the behavior of rubber compounds, both of which are predictable.
The relationship of air volume and pressure under varying temperature conditions is essentially covered by Boyle's Law, which was first put forth almost four hundred years ago and has been accepted, proven science in virtually all quarters for at least three centuries. The sole remaining denier worldwide is the National Football League in the United States.

An excellent info source is the blog www.rvtiresafety.com, written by Tireman9, (Roger Marble), a retired tire engineer. Tireman9 also frequents some of the RV fora, including iRV2.


John & Diane, fulltiming since '12 02 DS40, FL, Cat, '04 Element NHSO RVM103

[isa]

In the scientific world the International Standard Atmosphere (ISA) uses a temperature of 15*Celsius or 59*Fahrnheit at sea level with a standard pressure of 29.92" hg or 1013.2 mb. The standard lapse rate is 1.98*C/1000ft.

[JohnBoyToo]

Polyian,
the coach's recommended psi is only recommended for a fully loaded coach that is at it's GVWR.

Load it up any less and your tires are over inflated,
BUT over is MUCH better than under inflated as under inflated in the summer allows the sidewalls to 'squirm' more and heat up, so higher psi makes for a stiffer sidewall and less squirm, thus less heat gain...

[Trackrig]

Originally Posted by FatChance

I understand how ambient temperature affects cold tire pressure, but what temperature is cold tire recommended pressure based upon? I type this in SW Colorado where it will vary from the upper 30s tonight to the mid 70s tomorrow afternoon.

It's a nice to know piece of info, but don't over think / over worry this.

Bill

[Crasher]

Here is what works for me. In WI after weighing all six wheel positions, I find the minimum psi needed for the load they are carrying. I then add 5-10% depending on position and on a 60* morning set all pressures accordingly. Last year I was able to travel over 10,000 mile from WI to CO, UT, AZ, CA, NM, up to 11,000' and in temps ranging fro 30* up to 75* (cold morning temps) and not once did I have to add or release any air in seven months. The pressures were always above the minimum cold psi and never above the max cold. I don't know why it has to be more complicated than that.

[m.elliott63]

Originally Posted by Polyian

If you drive from Sea Level to 5000 ft you will also see a pressure drop: Tire Tech Information - The Influence of Altitude Changes on Tire Pressure

I know this stands to reason but here is the odd thing. We just finished a 10 day trip from flat land Indiana to Colorado, NM, Utah, AZ and back. I diligently checked my tire pressure every morning. No matter where we were (8100 ft was maximum I saw posted), My tire pressure remained spot on the same day after day. It seems to me that ambient air temperature has more effect than elevation. Last week when I got back, I had to adjust the pressure in both of our DD's due to big temperature swings the low pressure light came on in both the Mini and the Jeep.

[firedoc]

Originally Posted by m.elliott63

I know this stands to reason but here is the odd thing. We just finished a 10 day trip from flat land Indiana to Colorado, NM, Utah, AZ and back. I diligently checked my tire pressure every morning. No matter where we were (8100 ft was maximum I saw posted), My tire pressure remained spot on the same day after day. It seems to me that ambient air temperature has more effect than elevation. Last week when I got back, I had to adjust the pressure in both of our DD's due to big temperature swings the low pressure light came on in both the Mini and the Jeep.

Do you have nitrogen filled tires?

[Steve Ownby]

Originally Posted by FatChance

I understand how ambient temperature affects cold tire pressure, but what temperature is cold tire recommended pressure based upon? I type this in SW Colorado where it will vary from the upper 30s tonight to the mid 70s tomorrow afternoon.

I believe the tire manufacturer's charts are based on an ambient of 68.