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Old 10-20-2021, 03:57 PM   #29
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Way to involved unless you are in Alaska in the winter and inflating tires when they are warmed indoors. That is not Ambient (Air temperature in the shade) There are similar charts for the military.


I think this forum is more concerned for normal highway service in the "lower 48 at temperatures from 0F to 100F AMBIENT.


Note a change of ambient of 100 degrees will only result in about a 20% change in tire inflation pressure. That's the reality of the "Gas Law"
It's not exactly rocket science. I'm in Alberta, home altitude is 3565ft, so it gets cold and as I said large temp. swings during the day in spring and fall.
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Old 10-20-2021, 04:30 PM   #30
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Originally Posted by MN_Traveler View Post
Oh my. This will be a lively discussion. The "safe" answer is never run them at all, even for a few minutes, if they are below their minimum. This is exactly why i add 10 psi above the charts ... so on cold mornings i dont have to go out and inflate them.

I have no doubt though that other members here will say otherwise.
Running a tire at the minimum required pressure for the load means it is operating at 100% capacity continuously. That's another reason I go by the Federal Tire Placard in the vehicle instead of load/inflation charts.
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Old 10-20-2021, 09:30 PM   #31
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All very interesting comments which have me thinking I should adjust my cold pressure up the 5 to 7 psi that it has dropped after night ambient temps have dropped. Not that I have any plans of traveling until spring with the exception of maybe a once a month 5 to 10 mile up the road and back trip to keep the fluids circulated. Be interesting to see where pressures are this spring when I get ready for our first camping trip.
Amazing though all the miles I put on a Big Truck crisscrossing all lower 48 states and never had a blowout or tire problem. I would check pressures before a 2800 mile run that could take 38 to 40 hours non stop except for fuel. while fueling i would Thump the tires, do a visual check, check Cat eyes tire pressure monitors and back on the road. That's how it goes with running Critical freight and a Husband and Wife team. Got to keep those wheels turning!!!!
Never had a blowout and never let the tires get excessive wear before changing, for new ones. Also amazing the miles I would get on a set of tires!!
No such thing as age out before wear out LOL.
I'm getting quite an education since I got the Motorhome, wondering how I made it all those years in a Big truck and survived!!!!
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Old 10-20-2021, 09:46 PM   #32
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All very interesting comments which have me thinking I should adjust my cold pressure up the 5 to 7 psi that it has dropped after night ambient temps have dropped. Not that I have any plans of traveling until spring with the exception of maybe a once a month 5 to 10 mile up the road and back trip to keep the fluids circulated. Be interesting to see where pressures are this spring when I get ready for our first camping trip.
Amazing though all the miles I put on a Big Truck crisscrossing all lower 48 states and never had a blowout or tire problem. I would check pressures before a 2800 mile run that could take 38 to 40 hours non stop except for fuel. while fueling i would Thump the tires, do a visual check, check Cat eyes tire pressure monitors and back on the road. That's how it goes with running Critical freight and a Husband and Wife team. Got to keep those wheels turning!!!!
Never had a blowout and never let the tires get excessive wear before changing, for new ones. Also amazing the miles I would get on a set of tires!!
No such thing as age out before wear out LOL.
I'm getting quite an education since I got the Motorhome, wondering how I made it all those years in a Big truck and survived!!!!
Before TPMS became such a talked about item and MH owners began to micro-manage tire pressures, all we had to do was inflate the tires to the sidewall pressures, carry that "Thumper" and know what to listen for. That system was simple and worked fine for decades. I guess that's just not accepted anymore.
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Old 10-20-2021, 10:09 PM   #33
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I recently noticed my cold pressure has decreased in all tires (by TPMS) by almost 7 pounds in the mornings with temps in the 40's. But within 10 driving miles they are back to normal pressure.
My question is, should I add more air at cold ambient temps to bring pressure to cold normal settings?
Yes. You should add more air if your cold tire pressure is 7psi below the recommended cold tire pressure. Then, donít worry if it goes above the maximum cold sidewall pressure. Tire pressure may increase by 20%, from cold, while driving. That increased pressure is not your cold tire pressure.
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Old 10-21-2021, 08:03 AM   #34
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Originally Posted by 1Motorhome View Post
All very interesting comments which have me thinking I should adjust my cold pressure up the 5 to 7 psi that it has dropped after night ambient temps have dropped. Not that I have any plans of traveling until spring with the exception of maybe a once a month 5 to 10 mile up the road and back trip to keep the fluids circulated. Be interesting to see where pressures are this spring when I get ready for our first camping trip.

Amazing though all the miles I put on a Big Truck crisscrossing all lower 48 states and never had a blowout or tire problem. I would check pressures before a 2800 mile run that could take 38 to 40 hours non stop except for fuel. while fueling i would Thump the tires, do a visual check, check Cat eyes tire pressure monitors and back on the road. That's how it goes with running Critical freight and a Husband and Wife team. Got to keep those wheels turning!!!!

Never had a blowout and never let the tires get excessive wear before changing, for new ones. Also amazing the miles I would get on a set of tires!!

No such thing as age out before wear out LOL.

I'm getting quite an education since I got the Motorhome, wondering how I made it all those years in a Big truck and survived!!!!


I think the difference is that there you would just inflate to max, and not worry about ride quality or handling (my guess is that the trailer does not really care how rough the ride is. ). When i adjust the tire pressure to the table load based pressure, i am chasing ride quality and handling. Period.

When i got my first rig 10 years or so ago, i inflated toe tires to sidewall pressure. Handling was absolutely awful. After adjusting tire pressures to load, handling was wonderful. Yes, using the table pressures means you are walking a line and need to monitor them, but it is worth it for the comfort and reduced driving stress.
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Old 10-21-2021, 08:25 AM   #35
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For those storing their coaches, Michelin (and I suspect others) recommends inflating tires to PSI on the sidewall while stored.


This directly from the Michelin RV Tire Guide.
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Old 10-21-2021, 08:41 AM   #36
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Originally Posted by 1Motorhome View Post
All very interesting comments which have me thinking I should adjust my cold pressure up the 5 to 7 psi that it has dropped after night ambient temps have dropped. Not that I have any plans of traveling until spring with the exception of maybe a once a month 5 to 10 mile up the road and back trip to keep the fluids circulated. Be interesting to see where pressures are this spring when I get ready for our first camping trip.
Amazing though all the miles I put on a Big Truck crisscrossing all lower 48 states and never had a blowout or tire problem. I would check pressures before a 2800 mile run that could take 38 to 40 hours non stop except for fuel. while fueling i would Thump the tires, do a visual check, check Cat eyes tire pressure monitors and back on the road. That's how it goes with running Critical freight and a Husband and Wife team. Got to keep those wheels turning!!!!
Never had a blowout and never let the tires get excessive wear before changing, for new ones. Also amazing the miles I would get on a set of tires!!
No such thing as age out before wear out LOL.
I'm getting quite an education since I got the Motorhome, wondering how I made it all those years in a Big truck and survived!!!!
Just lucky I guess!
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Old 10-21-2021, 09:35 AM   #37
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Yes. You should add more air if your cold tire pressure is 7psi below the recommended cold tire pressure. Then, donít worry if it goes above the maximum cold sidewall pressure. Tire pressure may increase by 20%, from cold, while driving. That increased pressure is not your cold tire pressure.

Minor correction. The numbers on the tire sidewall really mean:
Tire Max load. No increase in inflation above the pressure number will give an increase in load capacity. The "MAX LOAD" is just that. Tthe maximum load capacity of that tire.
The inflation number really is the MINIMUM inflation needed to support the stated Max Load. Yes I know the wording can me confusing. I have no idea why someone decided that "MAX Inflation xxx MAX Load yyy" was the best way to convey the instruction. Only excuse I can come up with is that they were too informed about tires and inflation and didn't realize that many would translate the "MAX Inflation" to mean at any time. They certainly didn't expect people to have the hot pressure displayed on their dash.
Even today only RV owners with aftermarket TPMS are the only people being given hot tire pressure numbers.
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Old 10-21-2021, 09:40 AM   #38
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For those storing their coaches, Michelin (and I suspect others) recommends inflating tires to PSI on the sidewall while stored.


This directly from the Michelin RV Tire Guide.



Yes this is a good plan. A benefit is the reduction in "Flat Spotting" where a tire goes out of round and the deflection can take a "set" of flat spot where the tire is in contact with the flat road surface. It can take many miles to "work itself out" but running the higher pressure will tend to keep the flat spot smaller. Not zero but smaller.
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Old 10-21-2021, 09:44 AM   #39
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I was iniitally going to react badly to this advise .... but after reading your post (several times) I think I just to not really understand at all what you are trying to say. Can you please try re-phasing to clarify? (the advise that you need a different cold tire inflation based on what the ambient pressure is runs counter to everything that is written and taught .... but again, I suspect there is something here that is not coming across clearly.....)
Then an example: assume you determined 75psi to be needed for the tires on an axle.
My list gives
Psi at 70degrF/ degrF/psi
71 psi/ 6F/psi
77 psi/ 6F/psi

75psi is in the middle of this so remember 6degrF/ psi.

Then when wanting to check the pressure at 100degr F ambiŽnt temperature, do 100-70 = 30 degrF hotter , devide by 6 is not coincidentially 5, so fill or you should read 5psi more cold, so 80 psi. Then dont lower it to 75psi, the tire needs the lesser deflection it gives, so lesser heatproduction, because cooling down is also worse, because of the smaller temperature-differences between rubber and in and outside tire air.

When ambiŽnt temperature 40degrF 40-70= -30 degr hotter so 30 degr colder, so you will read 30/5 = 5 psi less, so 70 psi. Then the other way around , more heating up but also more cooling down, so rubber still wont reach its critical temperature. Only difference then is that you may use the 75psi for better riding-quality and fuel-saving, but for savety, so your tires dont overheat not needed

At extreme colder or especially hotter ambiŽnt temperature this can go wrong, but in the range motorhomes are used this will be safe.

But I made the list in first place for those who have tmps with external sensors, wich temperature reading is worthless, because temperature at the end of the valve, and not of gascompound in the tire. Then you can only use the pressure reading, and calculate by head the temperature.
But even internal sensors can give , but less, deviation in the temperature.

The cold filling is an extra.


1Motorhome and Crasher , see it right that tmps brings also new worries. But if you then know why it gives strange reading, you dont worry anymore.
Then you can let tmps do what its made for, and that is to warn for sudden pressure- loss.
This then will be send to the recever-unit within 1 second( when 2 psi pressure loss), so a tmps-seller wrote me, their sensors ( tiremoni-system) sends normal reading every 90 to 120 seconds).
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Old 10-21-2021, 10:09 AM   #40
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Minor correction. The numbers on the tire sidewall really mean:
Tire Max load. No increase in inflation above the pressure number will give an increase in load capacity. The "MAX LOAD" is just that. Tthe maximum load capacity of that tire.
The inflation number really is the MINIMUM inflation needed to support the stated Max Load. Yes I know the wording can me confusing. I have no idea why someone decided that "MAX Inflation xxx MAX Load yyy" was the best way to convey the instruction. Only excuse I can come up with is that they were too informed about tires and inflation and didn't realize that many would translate the "MAX Inflation" to mean at any time. They certainly didn't expect people to have the hot pressure displayed on their dash.
Even today only RV owners with aftermarket TPMS are the only people being given hot tire pressure numbers.
Yes, it is simultaneously, the maximum cold pressure and the minimum pressure recommended to support the maximum load. In most cases. Correct me if necessary, but does the wording on the tire not say “Max cold pressure” or Max cold psi”, and is that not what it means? And shouldn’t a basic understanding of the the term “cold” which has been explained ad nauseum, make it easy to understand that pressure will increase as the tire warms, due to warmer temperatures, sun exposure or rolling down the road?

Oddly, on one of my passenger vehicles, equipped with Michelin tires, the minimum recommended pressure to support the maximum load of 1477lbs, is 36psi. Yet the sidewall shows a maximum cold pressure of 44psi.

Determining correct tire pressure should be one of the easiest things anyone could do. It doesn’t require anecdotal stories or complicated math. For a vehicle owner, it really is simple.
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Old 10-21-2021, 10:49 AM   #41
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Then an example: assume you determined 75psi to be needed for the tires on an axle.
My list gives
Psi at 70degrF/ degrF/psi
71psi/6F/psi
77psi/6F/psi

75psi is in the middle of this so remember 6degrF/ psi.

Then when wanting to check the pressure at 100degr F ambiŽnt temperature, do 100-70 = 30 degrF hotter , devide by 6 is not coincidentially 5, so fill or you should read 5psi more cold, so 80 psi. Then dont lower it to 75psi, the tire needs the lesser deflection it gives, so lesser heatproduction, because cooling down is also worse, because of the smaller temperature-differences between rubber and in and outside tire air.

When ambiŽnt temperature 40degrF 40-70= -30 degr hotter so 30 degr colder, so you will read 30/5 = 5 psi less, so 70 psi. Then the other way around , more heating up but also more cooling down, so rubber still wont reach its critical temperature. Only difference then is that you may use the 75psi for better riding-quality and fuel-saving, but for savety, so your tires dont overheat not needed

At extreme colder or especially hotter ambiŽnt temperature this can go wrong, but in the range motorhomes are used this will be safe.

But I made the list in first place for those who have tmps with external sensors, wich temperature reading is worthless, because temperature at the end of the valve, and not of gascompound in the tire. Then you can only use the pressure reading, and calculate by head the temperature.
But even internal sensors can give , but less, deviation in the temperature.

The cold filling is an extra.


1Motorhome and Crasher , see it right that tmps brings also new worries. But if you then know why it gives strange reading, you dont worry anymore.
Then you can let tmps do what its made for, and that is to warn for sudden pressure- loss.
This then will be send to the recever-unit within 1 second( when 2 psi pressure loss), so a tmps-seller wrote me, their sensors ( tiremoni-system) sends normal reading every 90 to 120 seconds).


Ok, i think i see what you are trying to do ... calculate needed inflation at a given temperature to give a "target" pressure should the tire cool down (or heat up) to 70 degrees. (Ideal gas law stuff). BUT, this presumes that the inflation charts are premised on "cold" being defined as 70 degrees. My understanding has always been that "cold" really means "ambient", regardless of whether it is 100 or zero degrees. This also makes sense from a mechanics perspective, as it is the pressure inside the tire that actually supports the load, and you will need that given pressure regardless of what the temperature is.

Thought experiment - assume your approach that you need say 75 psi at 70 degrees. But the ambient temperature is 30-40 BELOW zero (F). This approach would have you drastically reduce the pressure in the tire, to a point where it is virtually fully flat. Just does not make sense (at least to me).

Tireman - are you able to confirm/refute whether the inflation tables are premised on a 70F ambient?
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Old 10-21-2021, 10:52 AM   #42
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Tireman - are you able to confirm/refute whether the inflation tables are premised on a 70F ambient?

Not Tireman, but I can ABSOLUTELY refute that inflation tables are based on any specific ambient temperature.


Said another way, the are based on ambient temperature before driving. Might be 0 degrees F or 100 degrees F.
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