Tire pressure and temperature

[MemoriesByTheMile]

Over time we have seen multiple discussions about tires, pressure and temps.
Haven’t posted these in the past but thought these would be useful here as a reference. “Cold temp” pressure readings are designed to be at 65F. When it isn’t that cool (or warm) this helps me understand how much variance I can expect to see. This also helps explain why TPMS systems don’t complain when the tire temp climbs 10F, if there is a corresponding temperature change.
For instance, our front steer tires have a cold pressure of 130 psi (at 65F) but when they reach 125F on a warm day driving in the sun, that tire pressure is expected to be 147psi, a 17 psi increase. So I know not to panic.
These tables are from Bendix:

 

[Kevin D Pem]

Over time we have seen multiple discussions about tires, pressure and temps.
Haven’t posted these in the past but thought these would be useful here as a reference. “Cold temp” pressure readings are designed to be at 65F. When it isn’t that cool (or warm) this helps me understand how much variance I can expect to see. This also helps explain why TPMS systems don’t complain when the tire temp climbs 10F, if there is a corresponding temperature change.
For instance, our front steer tires have a cold pressure of 130 psi (at 65F) but when they reach 125F on a warm day driving in the sun, that tire pressure is expected to be 147psi, a 17 psi increase. So I know not to panic.
These tables are from Bendix:

So this information is where they were able to calculate the table

Scientific American Volume 8, Issue 36 | Scientific American

"Gutta Percha Water Pipes", "Oil of Roses", "Cheap Cough Mixture" and more

www.scientificamerican.com

 

[flyboy013]

Everything that I've read indicates that "cold tire pressure" is the pressure when the tire is cold. Meaning it hasn't been driven for at least 3 hours and the sun isn't beating down on it, typically increasing the temperature and pressure on that one side of the coach. My steer tires should be 110 psi cold and all the others are at 85 psi. As I'm prepping to depart, my desire is for my tire pressure to be the pressure I indicated. I do not believe I want to start off with my tire pressure higher just because it 30 degrees warm outside. I want my cold (say 95°F) steer tire pressure to be 110, not 117. If I have this wrong, please point me to a credible source for this info. Thanks

 

[Joe Hogan]

Here is some thoughts on tire pressure settings

https://www.tirerack.com/upgrade-garage/how-do-i-set-my-tire-air-pressure

 

[jadatis]

This " pigheaded Dutch selfdeclared tyrepressure specialist " also is in the smaller camp that states you have to calculate the tyrepressure back to an index temperature ( as Rimex calls it) .
Seen different index temperatures mentioned.
15 degr C / 59degr F
18 degr C/ 65 degr F
20 degr C / 68 degr F
21 degr C / 70 degr F
And even 25 degr C/ 77 degr F .

The temperature the tiremakers based their maxload on is the question. But small differences dont give that much difference, so for easy calculating on the road I use 70 degr F.

so on a hot day of say 110 degr F the "cold measured pressure" must be a bit higher to prevent overheating any part of tire-material, where its all done for.
The higher pressure then gives lesser deflection, so lesser heatproduction at same speed, wich compensates the lesser cooling down, by lesser temperature-differences between tire-material and in and outside tire air or gascompound.

So never blead down cold or warm pressure on a hot day, better keep lower speed to give lesser heatproduction.

When cold ambiënt temp the other way around, but then highening up to determined needed pressure is allowed for roadhandling and fuelsaving. Then tire-material stays even colder then critical.

This is all aranged by laws of nature, so if you fill at about 65 to 70 degr F the determined needed pressure, you can let it flow with temperature-change, and dont need to maniacally fill up and blead down every time. Only checking if in line.

 

[Kevin D Pem]

Here is some thoughts on tire pressure settings

https://www.tirerack.com/upgrade-garage/how-do-i-set-my-tire-air-pressure

I think that's a great guide!!!

 

[Kevin D Pem]

Here in is the problem!

I have no experience with blow outs ( not!!!). So it's not for me to give advice. I would guess most people here have never had one!!!

So why do we worry about it?

So while I was contemplating whether to respond, a passing camper had such a problem! Not making this up!!!

So I started thinking! My first thought was, what's the odds of that! Then I started thinking that of those I know that have had blow outs, they were on the road!

The average traveler travels roughly 300 mpd. In Kansas! Tire pressure is likely to change due to temperature BUT! That assessment is not true in areas I live!

So the manufacturers design around temperature change according to tire rack! But there is more to consider!

Load carrying capacity! I stick with D rather than the required C when I am in range of a C rated tire. Why you say? The load capacity is in correlation of tire pressure, and that gives me some latitude when I adjust tire pressure.

Now let me explain My comment about my location! 150 miles can change elevation 6000 feet, 200 miles 9000 feet.

Roughly 6psi increase in the days drive added or subtracted from your morning pressure check, with the possible being much more on an extended trip!

So I like simple, what seems excessive can lead to simple! Higher load rating, and nitrogen fill makes daily pressure checking something of an outdated practice for me!!!

 

[jadatis]

About altitude .
I once read that the absolute pressure in tire gives the deflection.
So even in vacuüm same absolute pressure gives same deflection, so heatproduction at same speed.

Circumstantial evidence of this is that with zero gaugepressure,with valve closed, still a litle weight can be caried by the tire, to give same deflextion. But when opening valve suddenly much less.

This means that high in the mountans you measure with a gauge higher pressure, because ambiënt pressure at that hight is lower, and gauge gives difference between absolute pressure in tire and ambiënt pressure.

A tmps sensor sends absolute pressure to the receving unit with display, wich substracts a standard 1013mbar/14.7 psi ambiënt pressure at sealevel from it.
So if temperature is the same, tmps gives lower pressure then gauge on hight.
But dont need to highen up, because absolute pressure stays the same.

With gauge though you have to measure a bit higher pressure, wich can be calculated with help of that graphics you gave.

So again the same as with changing ambiënt temperature, only checking is needed if in line with altitude change. Mostly change nothing.

 

[Kevin D Pem]

About altitude .
I once read that the absolute pressure in tire gives the deflection.
So even in vacuüm same absolute pressure gives same deflection, so heatproduction at same speed.

Circumstantial evidence of this is that with zero gaugepressure,with valve closed, still a litle weight can be caried by the tire, to give same deflextion. But when opening valve suddenly much less.

This means that high in the mountans you measure with a gauge higher pressure, because ambiënt pressure at that hight is lower, and gauge gives difference between absolute pressure in tire and ambiënt pressure.

A tmps sensor sends absolute pressure to the receving unit with display, wich substracts a standard 1013mbar/14.7 psi ambiënt pressure at sealevel from it.
So if temperature is the same, tmps gives lower pressure then gauge on hight.
But dont need to highen up, because absolute pressure stays the same.

With gauge though you have to measure a bit higher pressure, wich can be calculated with help of that graphics you gave.

So again the same as with changing ambiënt temperature, only checking is needed if in line with altitude change. Mostly change nothing.

You might think a little more about what you said!

Here are a couple examples:

1) a balloon has a designed strength. When filled with helium and set free it rises till the walls can no longer contain the pressure. As a side,a hot air balloon will not have the same problem because it can equalize.

2) a human can change elevation without a problem,as long as the compartment he is in has a regulated pressure. The change can be achieved as long as he takes the time it takes him to acclimatize to the new pressure.

Sometimes all one needs do is to consider what they experience, rather than what they must interpret from another persons reasonings!

 

[jadatis]

If you want to play with temperature and pressure, I can send you my made tirepressure/temperature calculator for dry and wet gascompound in tire.

In that wet part I am first, I think.
Is when enaugh water in tire to go over to gas . Dry is completely dry gascompound, like nitrogen -filling claims.

You can even play with altitude, in the red fields. Then you have to determine first the ambiënt pressure at that hight yourselves.

5 parts , and part 5 you can give tire mounted and filled with a compressor with no vessel in between, ambient temperature,humidity, and filled pressure, and it gives at what temperature in tire all the water is gas, so from that temperature the dry calculation counts. So then calculation in 2 parts.

Playing with it myself, I found out that with enaugh water in tire pressure in tire goes higher ( 5 psi at 75 degrC/167 degr F) but temperature in tire stays a bit lower.
So the claim of Nitrogen filling that tire stays cooler, is not true.

And for cold pressure change, dry and wet calculations are practically the same.

Best definition of cold pressure is when temperature of gascompound in tire is the same as the outside tire ambiënt temperature.
That is when no external factors and long enaugh not driven. This has become the definition in time.

If you want my spreadsheet, mail me at my hotmail.com adress with username jadatis.
combine yourselfes, spamm-machines cant this way.

Then I will send it in return.

But here a list of cold pressure at 70 degr F filled, and degr F change per psi.
But if you use it for 65 degr F filled, it wont give dramatic differences.

Then you only have to search back the pressures you fill, and remember that for global calculation, wich is acurate enaugh for the goal. And a bit more acurate then the 2% pressure change per 10 degr F rule.

70degrF./degrF/psi

20 psi/ 15,5F/psi

21 psi/ 15F/psi

22 psi/ 14,5F/psi

23 psi/ 14 F/psi

24 psi/ 13,5F/psi

25 psi/ 13,5F/psi

26 psi/ 13 F/psi

27 psi/ 12,5 F/psi

28 psi/ 12,5 F/psi

29 psi/ 12 F/psi

30 psi/ 12 F/psi

3 1psi/ 11,5 F/psi

32 psi/ 11,5 F/psi

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

149 psi/ 3 F/psi

177 psi/ 3 F/psi