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1Motorhome 10-20-2021 08:38 AM

Adjust tire pressure for cold weather??
 
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?

MN_Traveler 10-20-2021 08:58 AM

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.

Chargerman 10-20-2021 09:07 AM

Tire pressures should be set cold and this is why adjustment is usually needed as the seasons change. I wouldnít adjust if you happen to be traveling to a cooler or warmer area temporarily but if your where youíre going to be then you should adjust pressures based on their cold temperature pressure of the tires

dfuelman 10-20-2021 09:21 AM

Quote:

Originally Posted by Chargerman (Post 5956560)
Tire pressures should be set cold and this is why adjustment is usually needed as the seasons change. I wouldnít adjust if you happen to be traveling to a cooler or warmer area temporarily but if your where youíre going to be then you should adjust pressures based on their cold temperature pressure of the tires

This is the correct method. You will find that the tire will still only climb to the correct pressure, but by starting at the correct pressure you avoid the larger heat cycle. Heat is your enemy.

MN_Traveler 10-20-2021 10:07 AM

Quote:

Originally Posted by Chargerman (Post 5956560)
Tire pressures should be set cold and this is why adjustment is usually needed as the seasons change. I wouldnít adjust if you happen to be traveling to a cooler or warmer area temporarily but if your where youíre going to be then you should adjust pressures based on their cold temperature pressure of the tires



Notsure if i agree with this if you travel from a warm area to a cold area, and your morning tire pressure is below the minimum, if you dont adjust then and there, then you are running on an underinflated tire (at least for a while), and are risking tire damage.

davidceder 10-20-2021 10:23 AM

Hard to do
 
I put about 7 pounds extra in my tires and never adjust unless things go wrong. I mean if a cold front comes through I would have to find a station to add air. That is a PIA. Then I would need to let air out when the cold front moves through. Repeat, repeat repeat. I do not carry a pump as I don't have the space, want the weight or hassle. I have read on this forum from very reputable involved folks that they fill their tires at the beginning of the camping season and that is it unless they run into some problems. I live at 5000 feet so this AM is was 44 degrees at home and 64 degrees in Phoenix where I am headed. I topped them off at home and that is all. Sometimes I do indeed get an high pressure alert on my TPMS but I just silence it. During really hot seasons in AZ I might up my High Pressure limit on my TPMS so the alarms stop. Just my way of doing things.

You guys that adjust your times all the time, do you do that same thing with your cars?

Domo 10-20-2021 10:29 AM

All tire manufactures state that you should check your tire pressure in the morning before the vehicle has moved more than a mile.

They also will tell you to set the pressure to their chart pressures which they've determined by millions of miles of experience and testing for optimal performance. They also have made sure that their lawyers are happy and that those recommended pressures will keep them out of the courtrooms.

You determine your tire pressure based on weight - which is not part of this discussion (do it the way they suggest on their web sites - or follow any formula you wish to believe in).

The manufacturers understand that temperature increases; during the day, on one side of the rig due to sitting with the sun hitting that side, decreases when it snows or you go to higher/colder altitudes. They also understand that rolling the tires will increase pressures, as will air temperature increase, altitude change and "the phase of the moon." With ALL of those factors considered they made their charts and hope to keep us safe and on the road.

Yes, check your tires each morning before rolling - it's simple (TPMS can make it nearly brainless). Correct, as needed, for where/when you are.

Domo 10-20-2021 10:33 AM

1 Attachment(s)
Quote:

Originally Posted by davidceder (Post 5956642)
I put about 7 pounds extra in my tires and never adjust unless things go wrong. I mean if a cold front comes through I would have to find a station to add air. That is a PIA. Then I would need to let air out when the cold front moves through. Repeat, repeat repeat. I do not carry a pump as I don't have the space, want the weight or hassle. I have read on this forum from very reputable involved folks that they fill their tires at the beginning of the camping season and that is it unless they run into some problems. I live at 5000 feet so this AM is was 44 degrees at home and 64 degrees in Phoenix where I am headed. I topped them off at home and that is all. Sometimes I do indeed get an high pressure alert on my TPMS but I just silence it. During really hot seasons in AZ I might up my High Pressure limit on my TPMS so the alarms stop. Just my way of doing things.

You guys that adjust your times all the time, do you do that same thing with your cars?

No, you don't adjust your pressure during the day. Overinflation changes the profile of your tires and affects performance - at least according to the Michelin folks I've spoken to on three occasions - but some folks don't seem to believe them.

Here's a good read about tires from a manufacturer;

RoadTrip2084 10-20-2021 11:35 AM

One thing I haven't found is a reference for exactly what temperature the tire manufacturers use for their "cold" tire temp?

If I set my tires cold (before driving for the day) based on the recommended pressures for my weights, that seems like it could be a lot different if it's 32f vs 75f outside. But nobody seems to claim a standard for what "cold" means.

Domo 10-20-2021 11:40 AM

Quote:

Originally Posted by RoadTrip2084 (Post 5956727)
One thing I haven't found is a reference for exactly what temperature the tire manufacturers use for their "cold" tire temp?

If I set my tires cold (before driving for the day) based on the recommended pressures for my weights, that seems like it could be a lot different if it's 32f vs 75f outside. But nobody seems to claim a standard for what "cold" means.

Ambient is what they want - that's the air as you find it outside in the morning before you roll more than a mile.

"Cold" according to Bridgestone... "Tires are considered cold when the vehicle has been parked for three hours or more, or if the vehicle has been driven less than a mile (1.6 km)"

https://en.wikipedia.org/wiki/Cold_inflation_pressure

Persistent 10-20-2021 12:17 PM

Quote:

Originally Posted by RoadTrip2084 (Post 5956727)
One thing I haven't found is a reference for exactly what temperature the tire manufacturers use for their "cold" tire temp?

If I set my tires cold (before driving for the day) based on the recommended pressures for my weights, that seems like it could be a lot different if it's 32f vs 75f outside. But nobody seems to claim a standard for what "cold" means.

Setting tire pressure "cold" is not any given temperature. It is what ever the temperature is in the morning before rolling on the tires. Yes it could be 32f. Yes it could be 75f. It is what ever the morning temperature is.

See tire manufactures website for details. Don't try to read between the lines.

Kenny Loney 10-20-2021 12:26 PM

Cold or AMBIENT temperature, that’s when the tire temperature is the same as the air temperature, before gaining any heat buildup from driving. The standard used by virtually all tire manufacturers.
The only time that I had an issue was on a winter trip from home, north of Toronto ON to Florida. I set the tire pressure accordingly to the ambient temperature (minus 30F). MH rode and handled great, until after leaving the campground in southern GA, MH rode very rough and very poor handling. (Before TPMS). Next morning checked tire pressures. What was 70 & 80 at home became 90 & 100 in FL 80F.
If travelling between areas on different temperature, definitely check every morning before driving.
‘COLD’ a relative term, in February at home, when the temperature reaches 32F people get out shorts and a light sweater, counted 10 people in Costco one day in shorts , no jackets. Same 32F in FL, well much heavier clothes.

Ken

RVStitchy 10-20-2021 12:46 PM

To better understand the logic I have a question. Is the difference between cold and hot (ordinary highway running) temps always the same delta? Or will tires come up to the same hot temp regardless of the starting cold temps?

I have lived in South Florida for the last 50 years so not much experience with your frigid sub 40 temps.

I plan on recording this data with TPMS in the future but have no plans to be anywhere this year that is below 50F to experiment.

Fiesta48 10-20-2021 01:04 PM

Way over kill posted here. Check all tires in the spring and fall. And just before each trip. 5 psi difference due to temps won't hurt any tire.
Low pressure will. Doing this for 60+ years.

RoadTrip2084 10-20-2021 01:18 PM

1 Attachment(s)
Quote:

Originally Posted by RoadTrip2084 (Post 5956727)
One thing I haven't found is a reference for exactly what temperature the tire manufacturers use for their "cold" tire temp?

If I set my tires cold (before driving for the day) based on the recommended pressures for my weights, that seems like it could be a lot different if it's 32f vs 75f outside. But nobody seems to claim a standard for what "cold" means.

Okay, after a bit of "DuckDuckGo"ing, I've found at least one authoritative reference for this. Source: "COLD WEATHER RECOMMENDATIONS FOR ALL CATERPILLAR MACHINES - Excerpted from Operation & Maintenance Manual (SEBU5898-11-01)" (Link)

It would appear that pressure adjustment is warranted if you travel from a warm to a cold or cold to a warm location, or if the temps at your location change drastically.

In my neck of the woods, in spring and fall the daily temp. range can vary 30degrees. Since too low pressure is the main concern I'd fill my tires cold at the lowest ambient temp. I expect to drive them in, so long as the resulting warm tire pressures didn't exceed the sidewall limits.

Note that the difference in recommended pressure between normal/standard ambient cold inflation temp. (64 to 70deg F) and the recommended pressure at 32F is only 6% or 5lbs in my case.

See below:

Quote:

Tire Inflation Information SMCS Code: 4203 SEBU5898-11

Tires that are inflated below the recommended pressure will have shortened life. A tire that is inflated to the correct pressure in a 18 to 21įC (64 to 70įF) warm shop area will have an incorrect tire pressure in freezing temperatures.
Use dry nitrogen gas to inflate the tires. Nitrogen gas is N2. Dry nitrogen is recommended in order to eliminate ice crystals. Ice crystals could hold the valve stem open in the tire.

The table shows the correct pressures for tires that are inflated in an area with a temperature
of 18 to 21įC (64 to 70įF). These pressures are adjusted for the environmental working temperature of the machine.

Tire inflation should be done in a heated area. The tire bead will seat better when the tire bead is warm. The initial tire pressure should be fifteen to twenty percent higher than the operating pressure in order to seat the tire bead against the rim. Deflate the tires to operating pressure before operating the machine. The contact surface of tires will become flat in cold weather when a machine is parked. To return the tire to a normal shape, move the machine gradually.

wolfe10 10-20-2021 01:36 PM

Quote:

Originally Posted by RoadTrip2084 (Post 5956845)
Since too low pressure is the main concern I'd fill my tires cold at the lowest ambient temp. I expect to drive them in


////


so long as the resulting warm tire pressures didn't exceed the sidewall limits.

See below:


Agree with the first half or your statement.


The second half not at all. The PSI on the sidewall is for cold (before driving), and has no relationship to PSI after driving. I promise that the tire engineers are familiar with the Ideal Gas Law and absolutely know what PSI change occurs with increased temperature.


I would be surprised if most tires do not exceed the side wall PSI if driven on hot days at highway speeds.

jadatis 10-20-2021 01:37 PM

Though its always needed to determine pressure with a reserve, for savety of tire ( so tire never overheats) the pressure-fluctuation by ambiŽnt temperature dont need care. If colder , the lower pressure gives more deflection , so more heatproduction a cycle, so at same speed, but also cooling down of tires rubber is better because of more temperature-differences between rubber and in and outside tire air. So rubber still not overheats.

Hotter outside the other way around.

So when 100degrF outside, you need higher cold pressure then when 40 degrF outside.

The advice pressure is determined for 70 degrF in tire so cold measured also ambiŽnt temp.
I made several lists for pressure/temperature relation, but became to complicated to use.
But now I made a simple list, wich is yust as complicated as is needed for the importance of the goal, so read simple.

In that list search the pressure you determined to be needed with a reserve, and read behind it the degrF/psi and remember that ( so for every axle , if different pressure, remember the degrF/psi).

Then on the road you can calculate by head the needed pressure for cold filling, or when reading tmps pressure while driving, you can calculate acurate enaugh the temperature of the gascompound in the tire.

Here it is:

33 psi/ 11 F/psi
34 psi/ 11 F/psi
35 psi/ 10,5 F/psi
36 psi/ 10,5 F/psi
37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/psi
97 psi/ 4,5 F/psi
109 psi/ 4,5 F/psi
110 psi/ 4 F/psi
126 psi/ 4 F/psi
127 psi/ 3,5 F/psi
148 psi/ 3,5 F/psi

Tireman9 10-20-2021 02:19 PM

Quote:

Originally Posted by 1Motorhome (Post 5956521)
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 always inflate tires when they are at Ambient temperature and not warmed from running or being in direct sunlight.
Depending on the pressure increase due to driving on tires in NOT CORRECT.


In my blog I recommend that the "set pressure" be at least 10% above the minimum pressure needed to support the heaviest load measured on the heaviest loaded tire.

Tireman9 10-20-2021 02:24 PM

Quote:

Originally Posted by davidceder (Post 5956642)
I put about 7 pounds extra in my tires and never adjust unless things go wrong. I mean if a cold front comes through I would have to find a station to add air. That is a PIA. Then I would need to let air out when the cold front moves through. Repeat, repeat repeat. I do not carry a pump as I don't have the space, want the weight or hassle. I have read on this forum from very reputable involved folks that they fill their tires at the beginning of the camping season and that is it unless they run into some problems. I live at 5000 feet so this AM is was 44 degrees at home and 64 degrees in Phoenix where I am headed. I topped them off at home and that is all. Sometimes I do indeed get an high pressure alert on my TPMS but I just silence it. During really hot seasons in AZ I might up my High Pressure limit on my TPMS so the alarms stop. Just my way of doing things.

You guys that adjust your times all the time, do you do that same thing with your cars?


You do not need to adjust your tires daily if you have a cushion. Pressure only changes about 2% for each change in ambient temperature of 10F, so having your "set pressure" at +10% you are good for a change in ambient of 50F which normally does not happen every day.


TPMS High pressure warning can be at +25% as you should not see that much increase unless running heavy and fast.


You do not need to adjust car tire pressure as most have the placard pressure at about +30% based on actual tire loading while RVs are lucky if they are set to +2% based on measured load.

RoadTrip2084 10-20-2021 02:27 PM

Quote:

Originally Posted by wolfe10 (Post 5956868)
Agree with the first half or your statement.


The second half not at all. The PSI on the sidewall is for cold (before driving), and has no relationship to PSI after driving. I promise that the tire engineers are familiar with the Ideal Gas Law and absolutely know what PSI change occurs with increased temperature.


I would be surprised if most tires do not exceed the side wall PSI if driven on hot days at highway speeds.

Yeah, that makes sense. Sidewall rating is max cold pressure required to support the max weight the tire can handle, which is hopefully quite a bit higher than the actual weight anyone needs it to on their rig.

MN_Traveler 10-20-2021 02:29 PM

Quote:

Originally Posted by jadatis (Post 5956871)
Though its always needed to determine pressure with a reserve, for savety of tire ( so tire never overheats) the pressure-fluctuation by ambiŽnt temperature dont need care. If colder , the lower pressure gives more deflection , so more heatproduction a cycle, so at same speed, but also cooling down of tires rubber is better because of more temperature-differences between rubber and in and outside tire air. So rubber still not overheats.

Hotter outside the other way around.

So when 100degrF outside, you need higher cold pressure then when 40 degrF outside.

The advice pressure is determined for 70 degrF in tire so cold measured also ambiŽnt temp.
I made several lists for pressure/temperature relation, but became to complicated to use.
But now I made a simple list, wich is yust as complicated as is needed for the importance of the goal, so read simple.

In that list search the pressure you determined to be needed with a reserve, and read behind it the degrF/psi and remember that ( so for every axle , if different pressure, remember the degrF/psi).

Then on the road you can calculate by head the needed pressure for cold filling, or when reading tmps pressure while driving, you can calculate acurate enaugh the temperature of the gascompound in the tire.

Here it is:

33 psi/ 11 F/psi
34 psi/ 11 F/psi
35 psi/ 10,5 F/psi
36 psi/ 10,5 F/psi
37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/psi
97 psi/ 4,5 F/psi
109 psi/ 4,5 F/psi
110 psi/ 4 F/psi
126 psi/ 4 F/psi
127 psi/ 3,5 F/psi
148 psi/ 3,5 F/psi

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.....)

MN_Traveler 10-20-2021 02:34 PM

Quote:

Originally Posted by RVStitchy (Post 5956810)
To better understand the logic I have a question. Is the difference between cold and hot (ordinary highway running) temps always the same delta? Or will tires come up to the same hot temp regardless of the starting cold temps?

I have lived in South Florida for the last 50 years so not much experience with your frigid sub 40 temps.

I plan on recording this data with TPMS in the future but have no plans to be anywhere this year that is below 50F to experiment.

The tires do NOT always come up to the same operating temperature with different outside temperatures. Generally speaking (but it is more complicated than this), the tires will see the same temperature change, increasing from their starting temperature.

So, if they generally see, say (just an example), a ten degree rise, if they start at 30 degrees, they will settle out at 40 degrees. But if they start at 100 degrees, they will settle out at about 110 degrees. another way of seeing this is that the pressure rise from starting pressure will be about the same, regardless of the temperature the tires started at. again, this is a general statement, and other things (like variations in load, direction of sun hitting tires, side winds, etc) will make for some degree of variation from the above statement.

Tireman9 10-20-2021 02:36 PM

Quote:

Originally Posted by RVStitchy (Post 5956810)
To better understand the logic I have a question. Is the difference between cold and hot (ordinary highway running) temps always the same delta? Or will tires come up to the same hot temp regardless of the starting cold temps?

I have lived in South Florida for the last 50 years so not much experience with your frigid sub 40 temps.

I plan on recording this data with TPMS in the future but have no plans to be anywhere this year that is below 50F to experiment.




Running pressure with no change in Ambient will usually be between +10% and + 20% which assumed the tires are not overloaded and you are not running faster than about 60 MPH AND that you set the "cold" pressure based on actual tire load and used the minimum inflation in the tables + 5% to +10%.


Run faster or heavier or not setting the initial pressure correctly will of course affect these numbers.

MN_Traveler 10-20-2021 02:39 PM

Quote:

Originally Posted by Fiesta48 (Post 5956829)
Way over kill posted here. Check all tires in the spring and fall. And just before each trip. 5 psi difference due to temps won't hurt any tire.
Low pressure will. Doing this for 60+ years.

Not so sure about the basic premise here. I once drove, in one day, from southern MO to minneapolis. When I left MO it was above freezing. When I hit minnesota, the ambient temperature was sub zero. Tire cold pressures were fine when I left MO. When I hit minnesota, the tire pressures were pushing their minimum inflation limit for load, while I was running at highway speed. so their equivalent "cold" pressure (say if I had stopped to rest for half an hour) would have been below the minimum cold inflation.

I never move my rig more than ten feet unless I know my tires are above minimum pressure.

Tireman9 10-20-2021 02:40 PM

Quote:

Originally Posted by wolfe10 (Post 5956868)
Agree with the first half or your statement.


The second half not at all. The PSI on the sidewall is for cold (before driving), and has no relationship to PSI after driving. I promise that the tire engineers are familiar with the Ideal Gas Law and absolutely know what PSI change occurs with increased temperature.


I would be surprised if most tires do not exceed the side wall PSI if driven on hot days at highway speeds.


Brett is 100% correct. I know as I am an actual tire design engineer.

Tireman9 10-20-2021 02:44 PM

Quote:

Originally Posted by RoadTrip2084 (Post 5956845)
Okay, after a bit of "DuckDuckGo"ing, I've found at least one authoritative reference for this. Source: "COLD WEATHER RECOMMENDATIONS FOR ALL CATERPILLAR MACHINES - Excerpted from Operation & Maintenance Manual (SEBU5898-11-01)" (Link)

It would appear that pressure adjustment is warranted if you travel from a warm to a cold or cold to a warm location, or if the temps at your location change drastically.

In my neck of the woods, in spring and fall the daily temp. range can vary 30degrees. Since too low pressure is the main concern I'd fill my tires cold at the lowest ambient temp. I expect to drive them in, so long as the resulting warm tire pressures didn't exceed the sidewall limits.

Note that the difference in recommended pressure between normal/standard ambient cold inflation temp. (64 to 70deg F) and the recommended pressure at 32F is only 6% or 5lbs in my case.

See below:




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"

Tireman9 10-20-2021 02:45 PM

Quote:

Originally Posted by jadatis (Post 5956871)
Though its always needed to determine pressure with a reserve, for savety of tire ( so tire never overheats) the pressure-fluctuation by ambiŽnt temperature dont need care. If colder , the lower pressure gives more deflection , so more heatproduction a cycle, so at same speed, but also cooling down of tires rubber is better because of more temperature-differences between rubber and in and outside tire air. So rubber still not overheats.

Hotter outside the other way around.

So when 100degrF outside, you need higher cold pressure then when 40 degrF outside.

The advice pressure is determined for 70 degrF in tire so cold measured also ambiŽnt temp.
I made several lists for pressure/temperature relation, but became to complicated to use.
But now I made a simple list, wich is yust as complicated as is needed for the importance of the goal, so read simple.

In that list search the pressure you determined to be needed with a reserve, and read behind it the degrF/psi and remember that ( so for every axle , if different pressure, remember the degrF/psi).

Then on the road you can calculate by head the needed pressure for cold filling, or when reading tmps pressure while driving, you can calculate acurate enaugh the temperature of the gascompound in the tire.

Here it is:

33 psi/ 11 F/psi
34 psi/ 11 F/psi
35 psi/ 10,5 F/psi
36 psi/ 10,5 F/psi
37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/psi
97 psi/ 4,5 F/psi
109 psi/ 4,5 F/psi
110 psi/ 4 F/psi
126 psi/ 4 F/psi
127 psi/ 3,5 F/psi
148 psi/ 3,5 F/psi




Nope. Too involved.

Tireman9 10-20-2021 02:49 PM

Quote:

Originally Posted by MN_Traveler (Post 5956942)
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.....)


jadats is Dutch so English is not his first language. He tries hard and does a better job than I would if I had to post in Dutch. Sometimes i think he tries too hard and we end up over complicated.

RoadTrip2084 10-20-2021 02:57 PM

Quote:

Originally Posted by Tireman9 (Post 5956966)
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.

Ray,IN 10-20-2021 03:30 PM

Quote:

Originally Posted by MN_Traveler (Post 5956552)
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.

:iagree::exactly: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.

1Motorhome 10-20-2021 08:30 PM

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!!!! :eek:

Crasher 10-20-2021 08:46 PM

Quote:

Originally Posted by 1Motorhome (Post 5957327)
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!!!! :eek:

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.

Kid Gloves 10-20-2021 09:09 PM

Quote:

Originally Posted by 1Motorhome (Post 5956521)
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.

MN_Traveler 10-21-2021 07:03 AM

Quote:

Originally Posted by 1Motorhome (Post 5957327)
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!!!! :eek:



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. [emoji4]). 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.

wolfe10 10-21-2021 07:25 AM

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.

RoadTrip2084 10-21-2021 07:41 AM

Quote:

Originally Posted by 1Motorhome (Post 5957327)
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!!!! :eek:

Just lucky I guess! :D

Tireman9 10-21-2021 08:35 AM

Quote:

Originally Posted by Kid Gloves (Post 5957372)
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.

Tireman9 10-21-2021 08:40 AM

Quote:

Originally Posted by wolfe10 (Post 5957614)
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.

jadatis 10-21-2021 08:44 AM

Quote:

Originally Posted by MN_Traveler (Post 5956942)
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).

Kid Gloves 10-21-2021 09:09 AM

Quote:

Originally Posted by Tireman9 (Post 5957711)
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.

MN_Traveler 10-21-2021 09:49 AM

Quote:

Originally Posted by jadatis (Post 5957729)
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?

wolfe10 10-21-2021 09:52 AM

Quote:

Originally Posted by MN_Traveler (Post 5957820)
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.

wvabeer 10-22-2021 08:24 AM

Quote:

Originally Posted by 1Motorhome (Post 5956521)
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?


NO!!!!!!!!!

Kid Gloves 10-22-2021 08:34 AM

Quote:

Originally Posted by wvabeer (Post 5958938)
NO!!!!!!!!!

Why would you advise to not add air to bring the tires to the recommended cold pressure?

Tireman9 10-22-2021 09:11 AM

Quote:

Originally Posted by Kid Gloves (Post 5957768)
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 ďMax cold pressureĒ or Max cold psiĒ, and is that not what it means? And shouldnít a basic understanding of the the term ďcoldĒ 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 doesnít require anecdotal stories or complicated math. For a vehicle owner, it really is simple.


Not all tires have the same wording on the tire sidewall except for the "Maximum Load".


Passenger car placard pressure is a recommendation from the vehicle dynamics and fuel economy engineers based on hundreds of miles testing and evaluating to find the right balance of ride, handling, noise and fuel economy. The pressure on most passenger cars provide 20 to 30% excess or reserve load capacity.
I have never heard of any RV company doing similar tire evaluations and from the numbers we see most select the smallest tire that will meet the DOT requirement for the tires to be able to support 100% of the GAWR with zero reserve load capacity.


Yes it would be nice if people read the literature and understood what "cold" inflation means but hardly a week goes by without someone asking how to calculate the pressure "correction factor" to set the pressure to the tire industry standard temperature.:banghead:


The tire wording is suppose to tell people and mean " The max load capacity for this tire is xxxx Lbs when inflated to yyy cold pressure, The load capacity will not be increased even if you increase the cold inflation above yyy cold pressure"

Tireman9 10-22-2021 09:23 AM

Quote:

Originally Posted by MN_Traveler (Post 5957820)
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?




The "Load & Inflation tables" are NOT based on any specific temperature number. The tables are based on a tire inflation pressure when the tire is at air AMBIENT temperature. Not artificially cooled or warmed




While there have been some tables developed and published for tire inflation when a tire is mounted and inflated in a heated workshop but will be driven in extreme cold ambient. Think Winter in Alaska This is done to prevent the need to park the vehicle, in the cold for a couple hours and then go and adjust tire inflation on big military vehicles. So unless you are inflating the tires on your RV in a heated garage at say 65F and intend to drive outside and head down the highway where it might be -40F I don't see the need for you to even have these charts.

wvabeer 10-23-2021 05:13 AM

Quote:

Originally Posted by Kid Gloves (Post 5958976)
Why would you advise to not add air to bring the tires to the recommended cold pressure?

You said it. cold pressure. If you have a leak yes but if they are all the same no. I use the tire manufacturers load pressure table for my tire. so right now at 40 my tires are in the 60's i'd say but after I get rolling they warm up and run about 90 to 100 depending on the air temp.

Kid Gloves 10-23-2021 07:20 AM

Quote:

Originally Posted by wvabeer (Post 5959809)
You said it. cold pressure. If you have a leak yes but if they are all the same no. I use the tire manufacturers load pressure table for my tire. so right now at 40 my tires are in the 60's i'd say but after I get rolling they warm up and run about 90 to 100 depending on the air temp.

Yes, I said ďcoldĒ. ďColdĒ is key. Take a look at the load and inflation table that you are using. See if the word ďcoldĒ appears on that document. There may even be a definition of ďcoldĒ.

ďColdĒ is a variable, a moving target. In your case, right now, ďcoldĒ is 40F. That is the temperature at which your tires need to be inflated to the recommended pressure.

The tires are no longer ďcoldĒ after youíve rolled down the road and ambient temperatures have increased. Those are exactly the wrong conditions to determine correct tire pressure. If that is how you are determining correct tire pressure, youíre doing it wrong.

jadatis 10-23-2021 08:47 AM

Quote:

Originally Posted by 1Motorhome (Post 5956521)
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?

Apart fom my pigheaded idea of calculating it back to 70degrF, we now can calculate back what pressure you filled cold at about 70 degr F.

40 degrF ambiŽnt temp drops almost 7 psi.
70-40= 30 degr/7psi is 4.3 degrF/psi.
Looking back in my list, 97psi / 4.5degrF/psi
126 psi/ 4 psi/ psi
So your used pressure is in between 97 and 126 psi. To be more presise I gamble on 110 psi.

Not because its needed, yust because it is able.
What pressure do you use?

I am now working on a long story, first in WORD , to explain why I still think the pressure needs to be calculated back to 70 degr F.

Chargerman 10-23-2021 08:53 AM

If the pressure needed to be calculated back to 70f donít you think the manufacturers would provide info to do so. Set it to the proper PSI cold. Done.

wolfe10 10-23-2021 09:07 AM

Quote:

Originally Posted by Chargerman (Post 5960009)
If the pressure needed to be calculated back to 70f donít you think the manufacturers would provide info to do so. Set it to the proper PSI cold. Done.


Quite likely we are discussing two different ways to arrive at the same inflation PSI.


One complex, one simple. Doesn't mean either is incorrect, but give me the easy one!

CraigRV2 10-23-2021 09:44 AM

Just a thought to share, I usually always add about 6~7 psi more pressure than listed (on the door jamb, never exceeding the tire max psi, least not very much if any) prior to the first cold snap when performing my Fall maintenance. Otherwise when the temps drop with the first significant fall\winter cold front my newer vehicles complain about low pressure in the tires (tpms) and my older vehicle's tires need more air as well, but with no tpms to warn me.

wolfe10 10-23-2021 09:52 AM

Quote:

Originally Posted by craigav (Post 5960052)
....when the temps drop with the first significant fall\winter cold front my newer vehicles complain about low pressure in the tires (tpms) and my older vehicle's tires need more air as well, but with no tpms to warn me.




Yup, your tires "read" the Ideal Gas Law and followed it to the letter.



Probably saying PV=nRT in their sleep.

Kid Gloves 10-23-2021 10:57 AM

Quote:

Originally Posted by wolfe10 (Post 5960020)
Quite likely we are discussing two different ways to arrive at the same inflation PSI.


One complex, one simple. Doesn't mean either is incorrect, but give me the easy one!

Yet some folks donít understand or follow the simple method. The last thing that needs to be introduced is some futile mathematical gymnastics based on an irrelevant data point.

Tireman9 10-23-2021 11:40 AM

Quote:

Originally Posted by wvabeer (Post 5959809)
You said it. cold pressure. If you have a leak yes but if they are all the same no. I use the tire manufacturers load pressure table for my tire. so right now at 40 my tires are in the 60's i'd say but after I get rolling they warm up and run about 90 to 100 depending on the air temp.




If I understand it you are depending on the heat from driving to get the tires to the needed minimum pressure. THIS IS ABSOLUTELY THE WRONG APPROACH.
When parked for a short time you do not need to adjust pressure. If parked for a long time say more than a few weeks over the winter you should inflate to the tire sidewall pressure to minimize tire "flat spotting".


You should ALWAYS ensure your tire inflation is correct BEFORE the tires are warmed by the sun AND BEFORE the tires are warmed from driving.

Tireman9 10-23-2021 11:41 AM

Quote:

Originally Posted by Chargerman (Post 5960009)
If the pressure needed to be calculated back to 70f donít you think the manufacturers would provide info to do so. Set it to the proper PSI cold. Done.


Correct

Tireman9 10-23-2021 11:43 AM

Quote:

Originally Posted by craigav (Post 5960052)
Just a thought to share, I usually always add about 6~7 psi more pressure than listed (on the door jamb, never exceeding the tire max psi, least not very much if any) prior to the first cold snap when performing my Fall maintenance. Otherwise when the temps drop with the first significant fall\winter cold front my newer vehicles complain about low pressure in the tires (tpms) and my older vehicle's tires need more air as well, but with no tpms to warn me.




Good plan to have a bit more ps than the minimum needed to support the load.

jadatis 10-23-2021 04:47 PM

Quote:

Originally Posted by Chargerman (Post 5960009)
If the pressure needed to be calculated back to 70f donít you think the manufacturers would provide info to do so. Set it to the proper PSI cold. Done.

In earlyer days, people did not mind about the temperature, and did not have tmps, so then yust advice was given for the average ambiŽnt temperature.

Also people could not check the pressure while driving by tmps , so did not worry about the pressure going over fi 80 psi for an E- load tire.

So why should you worry about it now.
So the manufacturers did not go with the time.

MN_Traveler 10-23-2021 07:26 PM

Quote:

Originally Posted by jadatis (Post 5960459)
In earlyer days, people did not mind about the temperature, and did not have tmps, so then yust advice was given for the average ambiŽnt temperature.



Also people could not check the pressure while driving by tmps , so did not worry about the pressure going over fi 80 psi for an E- load tire.



So why should you worry about it now.

So the manufacturers did not go with the time.



Because, if you drive the tire, even for a relatively short time, while it is below its min inflation for the load, you can damage the tire. The more times you do it, the more damage can accumulate.

Kid Gloves 10-23-2021 07:53 PM

Quote:

Originally Posted by jadatis (Post 5960459)
In earlyer days, people did not mind about the temperature, and did not have tmps, so then yust advice was given for the average ambiŽnt temperature.

Also people could not check the pressure while driving by tmps , so did not worry about the pressure going over fi 80 psi for an E- load tire.

So why should you worry about it now.
So the manufacturers did not go with the time.

Yes, the original TPMS, Dad with a pressure gauge before a trip, when the car hadnít been driven for hours. Ambient, cold, not artificially warmed, call it what you want. Why? Because physics. Who knew?

No need to worry, then or now, about a LR-E tire going above 80psi while in operation, even if it was necessary to inflate it to 80psi cold. Why? You guessed it, physics.

The best part of all of this is that we donít need to know a thing about physics, or gas laws, or the price of salmon in Norway. Just know the weight, check the load and inflation table and inflate accordingly. The hardest thing to understand is why this is so hard to understand.

MN_Traveler 10-23-2021 09:24 PM

Quote:

Originally Posted by Kid Gloves (Post 5960615)
Yes, the original TPMS, Dad with a pressure gauge before a trip, when the car hadnít been driven for hours. Ambient, cold, not artificially warmed, call it what you want. Why? Because physics. Who knew?



No need to worry, then or now, about a LR-E tire going above 80psi while in operation, even if it was necessary to inflate it to 80psi cold. Why? You guessed it, physics.



The best part of all of this is that we donít need to know a thing about physics, or gas laws, or the price of salmon in Norway. Just know the weight, check the load and inflation table and inflate accordingly. The hardest thing to understand is why this is so hard to understand.



Farmed Atlantic salmon or wild coho? [emoji4]

wvabeer 10-24-2021 04:03 AM

If you guys think you need to ad air on every colder morning then go ahead. I haven't had to ad air to my Sumitomo's in 5 years. While changing the batteries in my TPM's I evened the rears up as my ocd was bugging me. They still don't match because of temperature difference.

Kid Gloves 10-24-2021 08:14 AM

Quote:

Originally Posted by wvabeer (Post 5960767)
If you guys think you need to ad air on every colder morning then go ahead. I haven't had to ad air to my Sumitomo's in 5 years. While changing the batteries in my TPM's I evened the rears up as my ocd was bugging me. They still don't match because of temperature difference.

It isnít necessary to adjust tire pressures on every cold morning. Done correctly, there is no reason that side to side pressures canít be matched exactly.

What are your axle weights, what size tires are on your rig and to what pressures did you most recently set them?

R.Wold 10-24-2021 08:59 AM

Quote:

Originally Posted by Tireman9 (Post 5956972)
jadats is Dutch so English is not his first language. He tries hard and does a better job than I would if I had to post in Dutch. Sometimes i think he tries too hard and we end up over complicated.

That explains the umlaut:D

R.Wold 10-24-2021 10:53 AM

Quote:

Originally Posted by Chargerman (Post 5960009)
If the pressure needed to be calculated back to 70f don’t you think the manufacturers would provide info to do so. Set it to the proper PSI cold. Done.

The idea is that is not a linear equation and you need some base point from which to make the calculations. That done you can extrapolate to adjust for ambient temp and proceed. I think....or is it interpolate? No, it must be differentiate. :blink:

Personally I find myself more in 1Motorhome’s camp and don't get quite that far down in the weeds. I only recently added TPMS to my gadget collection and while I admit its value, I find it as much an annoyance/distraction as anything. For decades a morning thump with a hydrant wrench was sufficient, but I know thats sacrilege here and in all seriousness fire engines weren't operated like motorhomes, and a motor home can sustain a lot of damage from a tire failure.


Quote of the day:
Quote:

Originally Posted by Kid Gloves:
The hardest thing to understand is why this is so hard to understand.

ScottKB 10-24-2021 03:20 PM

Quote:

Originally Posted by Fiesta48 (Post 5956829)
Way over kill posted here. Check all tires in the spring and fall. And just before each trip. 5 psi difference due to temps won't hurt any tire.
Low pressure will. Doing this for 60+ years.

I set mine to cold set point on tires before each trip and leave it. I have not done the weight math or over inflate them at cold temp as some suggest. So far so good.

jrgator 10-24-2021 03:41 PM

So, I leave Florida in a couple of weeks with the morning ambient of 75. In North Carolina two days later when the morning ambient is 40, should I raise the Florida pressure from the Michelin recommended 85 to 90 before I leave as a hedge against the low pressure in N.C.?

Max Headroom 10-24-2021 03:57 PM

Quote:

Originally Posted by Domo (Post 5956652)
All tire manufactures state that you should check your tire pressure in the morning before the vehicle has moved more than a mile.

They also will tell you to set the pressure to their chart pressures which they've determined by millions of miles of experience and testing for optimal performance. They also have made sure that their lawyers are happy and that those recommended pressures will keep them out of the courtrooms.

You determine your tire pressure based on weight - which is not part of this discussion (do it the way they suggest on their web sites - or follow any formula you wish to believe in).

The manufacturers understand that temperature increases; during the day, on one side of the rig due to sitting with the sun hitting that side, decreases when it snows or you go to higher/colder altitudes. They also understand that rolling the tires will increase pressures, as will air temperature increase, altitude change and "the phase of the moon." With ALL of those factors considered they made their charts and hope to keep us safe and on the road.

Yes, check your tires each morning before rolling - it's simple (TPMS can make it nearly brainless). Correct, as needed, for where/when you are.


This ^^^^ is the correct answer.
Check in the morning, before you head out, boom, your done.
No one in CONUS is going to drive between such an extreme temp shift in one day that anything more than this is needed.
As the above mentions, when was the last time you got an accurate weight on the coach, and calculated the correct COLD tire pressure?
That is a much bigger concern than daily TP fluctuations from climate.

MN_Traveler 10-24-2021 04:02 PM

Quote:

Originally Posted by Max Headroom (Post 5961491)
This ^^^^ is the correct answer.
Check in the morning, before you head out, boom, your done.
No one in CONUS is going to drive between such an extreme temp shift in one day that anything more than this is needed.
As the above mentions, when was the last time you got an accurate weight on the coach, and calculated the correct COLD tire pressure?
That is a much bigger concern than daily TP fluctuations from climate.



Lol. Sorry. I HAVE driven through such large ambient temp fluctuations that adjustment (in both directions) , even within the same day, was needed. Does not happen often, but it can.

Ramrod 10-24-2021 04:17 PM

Quote:

Originally Posted by 1Motorhome (Post 5956521)
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?

I always check tire pressure and adjust to proper pressure per chassis manufacturer the morning before leaving. No matter where I am. Cold or hot ambient temperature. Period.

ldfeat 10-24-2021 05:27 PM

So, if I check tires on a cold morning and find that they are low by 10lbs, I'll drive a few miles to find a place to air them up. Of course driving will heat the tires and increase the pressure, so I'll merely put ten lbs in the tires no matter what the heated tire pressure is raised to. So, if the tires were at 90psi before driving, and they are supposed to be 100, I'll put 10 more lbs in them even if it raised to 100 because of driving heat. Just a FYI...Larry 2014 Reyo P

PBK Images 10-24-2021 06:22 PM

My understanding from Michelin is that the standard temp they use is 68F. Assuming that my OAT in the morning is 45F, and my front tires (with the weight that I am carrying) is recommended to be a minimum of 117psi. But I could go up to the max limit of the tire and/or wheel, say 130PSI, my inflation goal at 45F will be the minimum (117 PSI). Why? Because I know that the OAT will increase during the day and the tire temp will increase as I drive. Just using common sense. If it is much colder, say, 35F, and I know that after a mile or two the tires will heat up to 45F and then continue heating, I might "cheat" a pound or two and inflate to 115psi to avoid higher psi at operating temps. Everyone has their own thoughts.

Max Headroom 10-24-2021 07:02 PM

Quote:

Originally Posted by MN_Traveler (Post 5961499)
Lol. Sorry. I HAVE driven through such large ambient temp fluctuations that adjustment (in both directions) , even within the same day, was needed. Does not happen often, but it can.

That's a serious case of overthinking, on steroids. OTR trucks go from places like Denver to Phoenix in one trip, in one day. Trust me, they are not doing this.
Are you adjusting your tires for fuel burn every couple of hours too?


A tire that is running and up to temp will be just fine, even if you go from Death Valley, to Vail. Checking the cold pressure where ever you are in the morning will be close enough, and what is recommended on the data sheet for the cold load pressures. There is no hot pressure table for any commercial tire that I've ever seen.
If the tire mfgrs thought this was necessary and prudent, they would recommend it, and they don't. Same goes for whats in the coach owners manual. As others have said, all this has already been thought of by the tire makers, when they published the cold inflation specs.
And if you are 'interpolating' what your hot TP 'should be', and adjusting based on that, then you're basically just guessing, and certainly not following the mfgrs recommended safe practice.


For a while, I've been scratching my head as to why so many RV's have blow outs, and I think I have my answer...

MN_Traveler 10-24-2021 07:22 PM

Quote:

Originally Posted by Max Headroom (Post 5961724)
That's a serious case of overthinking, on steroids. OTR trucks go from places like Denver to Phoenix in one trip, in one day. Trust me, they are not doing this.
Are you adjusting your tires for fuel burn every couple of hours too?


A tire that is running and up to temp will be just fine, even if you go from Death Valley, to Vail. Checking the cold pressure where ever you are in the morning will be close enough, and what is recommended on the data sheet for the cold load pressures. There is no hot pressure table for any commercial tire that I've ever seen.
If the tire mfgrs thought this was necessary and prudent, they would recommend it, and they don't. Same goes for whats in the coach owners manual. As others have said, all this has already been thought of by the tire makers, when they published the cold inflation specs.
And if you are 'interpolating' what your hot TP 'should be', and adjusting based on that, then you're basically just guessing, and certainly not following the mfgrs recommended safe practice.


For a while, I've been scratching my head as to why so many RV's have blow outs, and I think I have my answer...



Max - dont be nasty ... that was uncalled for.

When i drove from warmer to subzero temps, my tire pressures went from significantly above the min inflation (cold), down to the min inflation, WHILE I WAS DRIVING. I was concerned about them dropping lower if i stopped for any length of time.

I believe truckers usually just run the sidewall pressure. But then again, the trailer contents is usually not too worried about the quality of the ride...

I think im done with thread ... you folks do what you want to. (Ive heard some pretty dangerous practices here)

Crasher 10-24-2021 07:51 PM

Is there any topic that has as many opinions than the Tire Pressure saga? There is a Sticky with proven facts from an actual tire engineer/expert available to all, and yet, rather than read it, another tire pressure question is posted and more non-expert opinions are offered. :banghead:

Kid Gloves 10-24-2021 08:10 PM

Quote:

Originally Posted by PBK Images (Post 5961673)
My understanding from Michelin is that the standard temp they use is 68F. Assuming that my OAT in the morning is 45F, and my front tires (with the weight that I am carrying) is recommended to be a minimum of 117psi. But I could go up to the max limit of the tire and/or wheel, say 130PSI, my inflation goal at 45F will be the minimum (117 PSI). Why? Because I know that the OAT will increase during the day and the tire temp will increase as I drive. Just using common sense. If it is much colder, say, 35F, and I know that after a mile or two the tires will heat up to 45F and then continue heating, I might "cheat" a pound or two and inflate to 115psi to avoid higher psi at operating temps. Everyone has their own thoughts.

There is no standard temperature. Where did you find a load and inflation chart that recommends 117psi? You need to round up in 5psi increments to 120psi. Why would you ever inflate to less than the recommended minimum cold pressure?

Higher psi at operating temperatures is normal. Itís physics, itís inescapable. You are not using common sense.

NXR 10-24-2021 08:20 PM

Quote:

Originally Posted by jrgator
So, I leave Florida in a couple of weeks with the morning ambient of 75. In North Carolina two days later when the morning ambient is 40, should I raise the Florida pressure from the Michelin recommended 85 to 90 before I leave as a hedge against the low pressure in N.C.?

The minimum pressure I use is 90 PSI. "Minimum" as in not underinflated at all and coincidentally is also the inside DOT sticker. So 90 PSI can fully support the GAWR of each axle.

I usually set the tires to 98 or so to give me some temperature margin.

When I leave Florida at the end of March I bring all of the tires up to 100 PSI from the 95 PSI or so they usually are at that time.

When I arrive in Cleveland, OH and the temps are in the low 40's to high 30's, the next morning the tires are sitting at 90 PSI or a tad more.

It works for me.

We'll be leaving here in late December for Florida so I'll have the tires here at about 95 PSI. Whatever they are when we get to Florida will be where they stay unless somehow they are over the maximum sidewall cold pressure of 110 PSI. That has not happened yet.

I put air in the tires twice a year, when we leave Florida in early Spring and in the late Fall before we leave northern Ohio.

FWIW,

Ray

BigBillSD 10-25-2021 09:40 AM

Why wouldn't the tire pressure recommendations be to a corrected temperature like maybe 70 degrees? Using a TPMS allows you to see your tire pressures rise within a minute or so of starting to drive. My tires usually run at the same (130lbs) pressure when its 60 degrees outside and at 110 degrees outside, and they start at 115lbs cold. I have watched that many times driving from San Diego over toward Yuma on the way out of town. Changing the pressures every morning due to the outside temperature sounds more like an old wives tale.. (or more appropriately a senile engineer's tale) Or, we have always done it that way mentality. Within a few minutes your tires are hot. Maybe we are saying that its those first couple miles that kill the tire, as after that the pressure & tire temp rise pretty fast. -Bill

PS. This should "heat" up the discussion..

Kid Gloves 10-25-2021 11:10 AM

Quote:

Originally Posted by BigBillSD (Post 5962319)
Why wouldn't the tire pressure recommendations be to a corrected temperature like maybe 70 degrees? Using a TPMS allows you to see your tire pressures rise within a minute or so of starting to drive. My tires usually run at the same (130lbs) pressure when its 60 degrees outside and at 110 degrees outside, and they start at 115lbs cold. I have watched that many times driving from San Diego over toward Yuma on the way out of town. Changing the pressures every morning due to the outside temperature sounds more like an old wives tale.. (or more appropriately a senile engineer's tale) Or, we have always done it that way mentality. Within a few minutes your tires are hot. Maybe we are saying that its those first couple miles that kill the tire, as after that the pressure & tire temp rise pretty fast. -Bill

PS. This should "heat" up the discussion..

Well Bill, there is information provided by tire manufacturers from which knowledge can be gained.

inkahauts 10-25-2021 12:52 PM

If you really want to worry less about fluctuations in pressure you could find a place that could drain all the air from your tires and replace it with nitrogen air. It will have far less fluctuations between cold pressure and driving pressure. And then only add nitrogen air when it needs any more at some point.

BigBillSD 10-25-2021 01:22 PM

Quote:

Originally Posted by Kid Gloves (Post 5962455)
Well Bill, there is information provided by tire manufacturers from which knowledge can be gained.


I have, but so far only Michelin mentions it. And now that I look on their site for a few minutes, I have not found it. Michelin gave us a handout during an escapees seminar, and theirs said tire pressures should be corrected to 68 degrees on what I remember was an official glossy Michelin handout. Its too bad that this last year I was so bored the first couple months I started purging the house of unneeded crap. All that old paperwork went into the recycle bin. I don't use Michelin's anyway.

I only top up my tires when its around 70 degrees in the morning. They have about 50k miles now, and will be aging out in the next couple years. -Bill

Kid Gloves 10-25-2021 02:50 PM

Quote:

Originally Posted by BigBillSD (Post 5962648)
I have, but so far only Michelin mentions it. And now that I look on their site for a few minutes, I have not found it. Michelin gave us a handout during an escapees seminar, and theirs said tire pressures should be corrected to 68 degrees on what I remember was an official glossy Michelin handout. Its too bad that this last year I was so bored the first couple months I started purging the house of unneeded crap. All that old paperwork went into the recycle bin. I don't use Michelin's anyway.

I only top up my tires when its around 70 degrees in the morning. They have about 50k miles now, and will be aging out in the next couple years. -Bill

Perhaps Michelin punted on the idea of a temperature correction factor after realizing that a large percentage of owners canít figure out how to properly inflate their tires when give the simplest of instructions.

MN_Traveler 10-25-2021 03:15 PM

Quote:

Originally Posted by inkahauts (Post 5962601)
If you really want to worry less about fluctuations in pressure you could find a place that could drain all the air from your tires and replace it with nitrogen air. It will have far less fluctuations between cold pressure and driving pressure. And then only add nitrogen air when it needs any more at some point.

oh my .... not this again. Air is almost 80% nitrogen, most of the rest of the balance being oxygen. Both of these gases behave almost identically to each other to changes in pressure and temperature (ideal gas law). I am afraid that this commentary that continues to propagate that nitrogen filled tires will vary less in pressure than air filled tires is, with apologies, just plain not right ... and this is fact and data based, not just opinion. And yes, I can supply that data if someone says "where are the data"

Nitrogen filled tires do have a place - if it is dry nitrogen, when used over 5 years or so, might reduce the internal damage to the tire due to oxidation and hydrolysis or rusting of metalic components (damage by chemical reactions with water). I also understand (dont hold me to this though) that in racing and jet planes, nitrogen filled tires can be used to reduce the risk of fire due the presence of oxygen that would otherwise be in filled tires ... and also to reduce the damage that oxygen can do to tires. But nitrogen has no effect on the tires ability to hold pressure, or reduce pressure changes with temperature.....

(ok ... I broke my promise to stay away from this thread. Tireman and Crusher .... PLEASE, hold my arms behind me and hold me back..... :-)

Cass Sumrall 10-25-2021 03:18 PM

Quote:

Originally Posted by Fiesta48 (Post 5956829)
Way over kill posted here. Check all tires in the spring and fall. And just before each trip. 5 psi difference due to temps won't hurt any tire.
Low pressure will. Doing this for 60+ years.

Agreed!

RoadTrip2084 10-25-2021 04:06 PM

Quote:

Originally Posted by BigBillSD (Post 5962648)
I have, but so far only Michelin mentions it. And now that I look on their site for a few minutes, I have not found it. Michelin gave us a handout during an escapees seminar, and theirs said tire pressures should be corrected to 68 degrees on what I remember was an official glossy Michelin handout. Its too bad that this last year I was so bored the first couple months I started purging the house of unneeded crap. All that old paperwork went into the recycle bin. I don't use Michelin's anyway.

I only top up my tires when its around 70 degrees in the morning. They have about 50k miles now, and will be aging out in the next couple years. -Bill

The Caterpillar reference I included back in https://www.irv2.com/forums/f258/adj...ml#post5956845 mentions

"The table shows the correct pressures for tires that are inflated in an area with a temperature
of 18 to 21įC (64 to 70įF)." So that would be considered the default temp. range for cold tire inflation.

MN_Traveler 10-25-2021 04:44 PM

Quote:

Originally Posted by RoadTrip2084 (Post 5962842)
The Caterpillar reference I included back in https://www.irv2.com/forums/f258/adj...ml#post5956845 mentions

"The table shows the correct pressures for tires that are inflated in an area with a temperature
of 18 to 21įC (64 to 70įF)." So that would be considered the default temp. range for cold tire inflation.

Im sorry - I do not see an interpretation there that implies that you should then adjust the pressures in the tires at colder temperatures so that if the tires were to hit those "reference" temperatures then their pressures would correspond to the pressures they used at those temperatures.. sorry - it does not make sense (physically and mechanically) that at much colder temperatures you would inflate the tires to a LOWER pressure - which would then be unable to support the load (which has not changed with temperature) without overly flexing. sorry .... but to me that is a totally incorrect, and dangerous, interpretation of what they are saying in that publication.

BigBillSD 10-25-2021 05:39 PM

Quote:

Originally Posted by Kid Gloves (Post 5962728)
Perhaps Michelin punted on the idea of a temperature correction factor after realizing that a large percentage of owners canít figure out how to properly inflate their tires when give the simplest of instructions.


Good Point! It says 120 lbs on my tires, that's the pressure I should run.. Right. :whistling: -Bill

Jacjetlag 10-25-2021 05:58 PM

"All tire manufactures state that you should check your tire pressure in the morning before the vehicle has moved more than a mile."

+++++

That said, colder air is more dense. A tire that is carrying thousands of pounds needs adequate pressure to perform as designed.

If you are too lazy to fill them or just ignorant , it is at your own peril.

https://www.youtube.com/watch?v=aiMIG4phsW4&t=23s

vlamgat 10-25-2021 06:05 PM

Quote:

Originally Posted by Domo (Post 5956658)
No, you don't adjust your pressure during the day. Overinflation changes the profile of your tires and affects performance - at least according to the Michelin folks I've spoken to on three occasions - but some folks don't seem to believe them.

Here's a good read about tires from a manufacturer;

I am surprised that it took so long for your comment's arrival to address the issue of PHYSICS. It seems the prevailing opinions are to forget physics and stick to the number. That air pressure in tires decrease about 1 psi per 10 degrees; and that the recommended pressure is at 20 deg C/68 F means that seeing a tire pressure that was at 65 when the temperature was 68 in the morning and rose to 71 when the out of the sun ambient was at 90 is quite normal. Similarly they will drop from 65 to 62 around freezing. Reinflating them to 65 is over inflating them.

There is a consensus that irrespective of the temperature there is a pressure below which you should not run the tire in order to retain bead integrity and that is recommended by Michelin and Continental ( the only OEMs that I have seen this discussed ) at 75% of the rated temperature.

However this is not an exact science and also one where most of the science is retained by the OEMs to avoid liability. But it does raise the question as to how impaired a tire becomes if the pressure is 5% over or under the tire maximum at maximum weight? I do not think anyone knows, not even the OEMs. So for some this will be a holier than thou life's work to maintain the "perfect" pressure while for others, if it will take a good kick, its ok.

RoadTrip2084 10-25-2021 07:06 PM

Quote:

Originally Posted by MN_Traveler (Post 5962886)
Im sorry - I do not see an interpretation there that implies that you should then adjust the pressures in the tires at colder temperatures so that if the tires were to hit those "reference" temperatures then their pressures would correspond to the pressures they used at those temperatures.. sorry - it does not make sense (physically and mechanically) that at much colder temperatures you would inflate the tires to a LOWER pressure - which would then be unable to support the load (which has not changed with temperature) without overly flexing. sorry .... but to me that is a totally incorrect, and dangerous, interpretation of what they are saying in that publication.

I think you're confused. The chart below the text shows the adjusted cold temp. tire pressure you should use for the equiv. normal cold tire pressure if you're dealing with COLD temps (32f and below). In each case the recommended pressure is higher than the default pressure.

MN_Traveler 10-25-2021 07:28 PM

Quote:

Originally Posted by RoadTrip2084 (Post 5963080)
I think you're confused. The chart below the text shows the adjusted cold temp. tire pressure you should use for the equiv. normal cold tire pressure if you're dealing with COLD temps (32f and below). In each case the recommended pressure is higher than the default pressure.

Ok - apologies. What the manual is saying (and this is a quote) is "tires inflated in a warm shop will be underinflated in cold temperatures". This is correct and makes sense. again - apologies.

What others are saying is exactly the opposite of what the linked manual is saying. THEY are saying that you should always maintain an inflation equivalent to what the tire contents would be (pressure wise) if they were shifted in temperature to some reference temp (like 68F). That is invalid, unsafe, and actually exactly opposite of what the linked manual is saying.

MN_Traveler 10-25-2021 07:37 PM

Quote:

Originally Posted by vlamgat (Post 5962982)
I Similarly they will drop from 65 to 62 around freezing. Reinflating them to 65 is over inflating them.

.

I am not quite positive what you are trying to say .... but if you are saying, as I think you are, that when the temperature is low, that you should NOT reinflate the tires to (as in your example) to, say, 65 .... that is just plain wrong and dangerous. See my just previous posting (where I apologized for misinterpreting what the poster was saying), then go read the quote I give in that posting, then go read the manual that for which that poster gave a link. it explicitly says that tires inflated in a warm shop (say 68F) will be underinflated when taken out into cold/freezing conditions. So ... if you are saying that if you actually have the tires out in freezing conditions, and you are reading a pressure that is below the minimum inflation for the load, that you should NOT reinflate the tires .... That is incorrect.

And to say that the manufacturers do not have any idea of what pressures cause damage to the tires (it is that damage, NOT unseating the bead as you apparently incorrectly claim) - that is also very sorely incorrect.

It is called engineering "testing".

This time I am truly and completely done with this thread.

Cactusbu11 10-25-2021 08:04 PM

Typically how many years can you get out of a tire even if the tread is still good?

Kid Gloves 10-25-2021 08:39 PM

Quote:

Originally Posted by BigBillSD (Post 5962955)
Good Point! It says 120 lbs on my tires, that's the pressure I should run.. Right. :whistling: -Bill

Well heck, if it says 120 right there on the tire, that must be the correct pressure, for you, and everyone else who puts that tire on their vehicle.

Brilliant!

NXR 10-25-2021 10:04 PM

Adjust tire pressure for cold weather??
 
But...when air gets colder it gets more dense and can support more weight. That's the concept of Density Altitude in aviation and why aircraft can take off in a shorter distance when it's cold than what it's hot.

https://www.faasafety.gov/files/gsla...%20branded.pdf

So if colder air is more dense why do we need to add pressure to tires when it gets colder? If the air in a tire truly is what supports the weight, shouldn't more dense air (cold air) be able to support more weight and not less?

Ray

MN_Traveler 10-25-2021 10:59 PM

Quote:

Originally Posted by NXR (Post 5963257)
But...when air gets colder it gets more dense and can support more weight. That's the concept of Density Altitude in aviation and why aircraft can take off in a shorter distance when it's cold than what it's hot.

https://www.faasafety.gov/files/gsla...%20branded.pdf

So if colder air is more dense why do we need to add pressure to tires when it gets colder? If the air in a tire truly is what supports the weight, shouldn't more dense air (cold air) be able to support more weight and not less?

Ray

Ok .... for a clearly serious, and actually very insightful question, I will try to answer .... because it might help cut through some of the misinformation on this thread.

Ray - this is actually a really good question - and the answer is that this is really mixing two very different aspects of physics.

A plane wing flies because of two things: the curved top of the wing which produces lower pressure on the top of the wing than on the bottom (the Bernoulli effect - which is is a pressure thing and has nothing to do with density), and the angle of attack of the wing (where, when the front of the wing is tilted upward and the wing pushed forward, air hitting the bottom of the wing is deflected downward, which exerts an upward force on the wing (newtons third law - when an object exerts a force on another object, the second object exerts an equal and opposit force on the first - strictly a density/mass thing, and has nothing to do with pressure).

Your density altitude thing is mostly a result of the angle of attack of a wing allowing it to "push" downward on the air - the denser (colder) the air, the stronger the upward force (because the air molecules are closer together, and the wing pushes more molecules downward for a given amount of forward motion .... kind of like throwing downward two baseballs versus one ... it takes more force to throw down two of them.

Inside a tire, there is no such "pushing" of air, and so its density becomes a non-issue. The ONLY thing acting inside a tire is the pressure the air exerts on the tread, walls, and rim of the tire. This works because a given pressure pushing on the tire "stiffens" the tire, and limits how much the sidewalls of the tire will deflect for a given load. If the pressure is lower, the tire sidewalls are not held stiffly in place, and can deflect more (very much like a very underinflated balloon is easy to squeeze and deform, but a highly inflated balloon is very stiff, and difficult to deform - it can support more weight without deforming.

To understand pressure - you really need to understand statistical thermodynamics .... but the simple explanation is that pressure is the result of lots and lots of gas molecules hitting the inside of the tire .... it is nothing more than that. It is the summation over time of many, many small "balls" (molecules) each with very very small mass and momentum hitting a wall. So .... the fewer the number of molecules inside the tire (like letting air out of the tire), the fewer will be hitting the wall in a given time, and the pressure is lower (the opposite is true when you add air to the tire.

As for temperature - it turns out that the speed a gas molecule flies through space is directly dependent on the temperature (the maxwell-boltzmann distribution). So for a tire with a certain amount of air in it, if the temperature goes down, the speed that the gas molecules are moving at goes down, and they each hit the inside of the tire with less momentum - and the pressure (and thus stiffness of the tire) goes down - for a given amount of weight on the tire, the tire deforms more. The tire may technically be supporting the weight, but upon each revolution it deforms more than if it were supported by a higher pressure - and it is this ongoing increased amount of deformation that causes increased stress and damage to the tire.

Kid Gloves 10-26-2021 06:40 AM

Thanks for coming back. Again.

So, would an airplane be able to take off in an even shorter distance, if it were inside a tire filled with compressed air?

MN_Traveler 10-26-2021 07:54 AM

Quote:

Originally Posted by Kid Gloves (Post 5963472)
Thanks for coming back. Again.



So, would an airplane be able to take off in an even shorter distance, if it were inside a tire filled with compressed air?



Lol. I guess. Would take a pretty big tire though [emoji4]

Tireman9 10-26-2021 11:03 AM

Quote:

Originally Posted by wolfe10 (Post 5956868)
Agree with the first half or your statement.


The second half not at all. The PSI on the sidewall is for cold (before driving), and has no relationship to PSI after driving. I promise that the tire engineers are familiar with the Ideal Gas Law and absolutely know what PSI change occurs with increased temperature.
Yes we do know that. It could be argued that we depend on that increase.

I would be surprised if most tires do not exceed the side wall PSI if driven on hot days at highway speeds.


Yes tire pressure can many times exceed tire sidewall number in real life operation. I doubt that the placard pressure for any RV is set based on engineering testing but are set simply based on Load & Inflation tables and regulatory minimums from NHTSA and RVIA.


Now we engineers also know that most passenger car tires would be an exception to the above general statement because their tire pressure is based on many dozens if not hundreds of in-car, and in laboratory engineering evaluations and the final number that goes on the placard is a balance of Ride, Handling, Fuel Economy, Noise and Traction and numerous other tests while it is possible that there is a motorhome model that had a Ride or handling evaluation, I have never heard of any motorhome company selecting any tire based on multiple in-vehicle evaluation or comparison test.

Examples: Most Passenger car tires have a recommended inflation pressure on the tire certification label that is significantly lower than the tire sidewall number, even though car companies have to meet similar minimum inflation numbers based on Federal Regulations. Don't forget to consider the percentage change, and not the absolute number of psi.
My personal cars have sticker / tire inflation of 36/51 (sticker is 29% lower) and 29/36 (sticker is 19% lower). My Class-C RV shows 65/80 on the certification sticker. These inflations are only sufficient to provide a Reserve Load of 1.9% Front and 2.9% rear.
If you stop and think about it, passenger cars having double digit reserve load capacity is probably a major reason for tire longevity in passenger car applications.

Tireman9 10-26-2021 11:36 AM

Quote:

Originally Posted by Max Headroom (Post 5961724)
That's a serious case of overthinking, on steroids. OTR trucks go from places like Denver to Phoenix in one trip, in one day. Trust me, they are not doing this.
Are you adjusting your tires for fuel burn every couple of hours too?


A tire that is running and up to temp will be just fine, even if you go from Death Valley, to Vail. Checking the cold pressure where ever you are in the morning will be close enough, and what is recommended on the data sheet for the cold load pressures. There is no hot pressure table for any commercial tire that I've ever seen.
If the tire mfgrs thought this was necessary and prudent, they would recommend it, and they don't. Same goes for whats in the coach owners manual. As others have said, all this has already been thought of by the tire makers, when they published the cold inflation specs.
And if you are 'interpolating' what your hot TP 'should be', and adjusting based on that, then you're basically just guessing, and certainly not following the mfgrs recommended safe practice.


For a while, I've been scratching my head as to why so many RV's have blow outs, and I think I have my answer...


Yes Underinflation, which for the tire is about the same as overloading, IS a primary reason for belt separations and shorter tire life. The data from tens of thousand RV scale readings at FMCA and Escapees and other events tells us that a MAJORITY of RV have one or more tire in overload.


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