Tire inflation question related to ambient temperature

[rvguy02]

We keep our Entegra Classic (2012 Aspire non-tag) in a climate controlled warehouse. Temps never drop below 40F. We’re leaving this Saturday to head to Florida and have a concern about tire pressure vs temperature. The day we leave, outside temperatures will be around 20-25F. Should I check pressure and modify as needed for ambient temperatures inside the warehouse or the outside temperature that will be 15-20 degrees colder? To allow the tires to reach outside temperatures, I’d have to leave it out for probably 45-50 minutes. I’ll have no choice the next morning as ambient temps at the campground will be around 20F. Daytime temps on our drive Sunday will be around 40F. I’m sure my tire pressures will be 3-4 psi lower Sunday morning. I’ll inflate accordingly.

No doubt we’ll have to deal with this same concern on our tow dolly.

Thanks for any input on this.

[rvguy02]

Just to clarify, we’ll be loading the coach inside of the warehouse, so it will be at least 40F in the warehouse as well as the tire temperatures.

[l1v3fr33ord1]

Susie and Stuart-

1) Check and set the tire pressures at your storage facility, before you roll.
2) Do the same on Sunday morning, before you roll.

I suspect that after Sunday morning the ambient temps at departure will increase. If so, and your tires are at or below the maximum cold inflation pressures, you may not need to adjust them again until you get to Florida. It's always your choice to do so, though.

A TPMS system on coach, dolly and toad rear tires helps greatly with the "check" task.

[jadatis]

When cold ambiënt temperature, you may highen up to recomended pressure, but is not needed for safety, so for that your tires wont overheat.

The other way around, hot ambiënt temps, you must certainly not let out air to recomended pressure, because cooling down of tirematerial is worse because of smaller tempdifferences between tire material and in and outside tire air.

Will give a list assumed filled cold at 70 degr F and degr F change per psi, easy to calculate with , and acurate enaugh for the goal.
But if you use it for 60 degr F cold filled, it wont give dramatic differences. And still more acurate then rules of tumb given in fora.

Then you will write that tmps gives also temperature, but external sensors give, probably verry acurate, the temp at the end of the valve and not the tire inside.

In next post I will give long story about why you dont have to worry about temp change.
Used it in anotger topic.

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
31 psi/ 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

[jadatis]

Dont pin me down on the exact temperatures, but here it is

Why pressure should be calculated back to 70 degrF
That pressure of tires is related to the temperature of gascompound in tire, is fact.
But that for instance you need for 100 degrF ambiënt temperature higher cold filled pressure, then for 70 degrF, and for 40 degrF can do with lower pressure then for 70 degrF, is a conclusion I took, and is the discussion here.
I am going to explain how I came to this conclusion.
I once had a long telephone call with a man from Vredestein , and he explained that goal of pressure determination and maxload of tire, is to not overheat them.
He explained that the molecule-structure of natural rubber can be compared to spagetti, and if you push your nail in it the print remains . Then the “ spagetty-strings" slide over each other.
Tires are vulcanised at the end, and this makes sulfurbridges between the “ spagetti “ wich makes the rubber flexible, so when you push your nail in it , the print directly dissapears, the rubber goes back to its original shape.
The rubber needs a certain amount of sulfurbridges, but to much makes the rubber hard, and if then bending of the rubbber, by the deflection and flexing back every cycle, gives small cracks, wich dont disapear ( logical)
When rubbers temperature goes above a critical temperature, to many sulfur bridges are created,and rubber hardens. Wich temperature this is I dont know, but the vulcanising proces is at 170 degrC is 340 degrF.
Rest is my Einstein way of thinking, and because my average IQ is probly half of that of Mr Einstein, change is 2ce as much that my theory is proven wrong once.
The temperature of the rubber is created by the balance between heating up a second and cooling down a second.
When you begin driving at cold pressure in ambiënt temperature of 70degrF, in-and out-side-tire air and all the rubber of tire is 70 degrF. The heat-transport then is zero. In basics Maxload is calculated for reference-pressure ( E-load 80 psi) and reference-speed ( P- and LT tires mostly 99mph/160kmph) so when you drive that speed constant with maxload on tire and reference-pressure cold filled in tire, no overheating of any part of tire. I practice a bit more complicated.
Yust for the example say you then drive 99mph constant speed, with referencepressure of 80psi ( E-load) and maxload on tire. In the beginning cooling down is marginal, because temperaturedifferences between rubber of tire and in and outside tire gascompound is still zero, but driving long enaugh rubber yust below its critical temperature in the middle of the thickest parts of tire, and at the edges , where rubber meats the gascompound, lets say 300 degrF.
Inside tire gascompound I state as 140degrF. Outside the tire always air 70 degrF

Then temperature difference between edges of rubber and inside tire gascompound 300-140=160 degrF., and between outside tire air 300-70=230 degrF. Also the inside tire gascompound is cooled down mostly trough the rimm to the air outside the tire with only 140-70= 70 degr temperature difference so 160/70 = 2.28 times as much cooling down by the better transport trough the metal rimm.
So coolingfactor then inside tire 160/230=70% of outside tire. In and outside tire Together 230+160=390 degrF
The rubber temperature then stays in balance ,so heating up factor also 390 degrF.
But the deflection , so heatproduction a second at that speed, then is lesser then at cold pressure, because temp in tire 140degrF, wich gives higher pressure. 80 psi filled at 70 degrF becomes 92.9 psi at 140 degrF.

Now situation ambiënt temp 100 degr F.
Temp of rubber still max 300degrF.
Temperaturedifference rubber and outside tire air 300-100= 200 degrF
Temperaturedifference rubber and inside tire gascompound 70% of outside 200= 140 degrF.
Together200+140=340 degrF worth of cooling capacity
So temperature inside the tire 300-140= 160degrF.
So at 70degrF ambiënt temperature 390degrF worth of cooling capacity.
At 100degrF ambiënt temperature 340degrF worth of cooling capacity.
This has to be compensated by lesser heatproduction a second by lesser deflection of tire is 340/390=87.2 % of the heatproduction at 70degrF ambiënt temperature.
Now if 80psi filled at 70degrF
At 100F/85.4psi
At 140F/ 92.5psi
At 160F/ 96.1psi
So 92.5/96.1=96.25% of the surface on the ground then at 70degr F driving 99mph with maxload on tire. Rule of tumb I determined gives 0.9625^2= 92.64 times the deflection . If heatproduction goes lineair with the deflection ( I hope and not more), this gives 92.64% of the heatproduction.
Cooling down is 87.2% , so heating up is even still more then cooling down, if 300degrF is the critical temperature of rubber .
If you then lower the 85.4psi cold pressure at 100degrF ambiënt temperature to 80psi, as is stated to be allowed because cold filled is at ambiënt temperature, the pressure becomes at 160degrF 90.2psi instead of 96.1psi ,wich gives more deflection so heatproduction a second, so rubber of tire temperature goes above 300degrF, and it hardens and cracks.
In fact , because at 100degr heating up factor is 92.64% and cooling down factor is 87.2% at 100degrF ambiënt temperature of the 70degrF situation, you should even pump the tires up a little to give lesser heatproduction a second., so heating up factor goes also to 87.2

Now ambient temp 40degrF.
Outside tire 300- 40= 260 degrF worth of cooling down factor.
Inside tire 300- ( 70% of 260= 182 degrF)= 118 degrF inside tire gascompound
So cooling down factor 260+182= 442 degrF
This is 442/390= 113.3% of coolingdown factor then at 70 degrF.
Then at 40 degrF 80psi filled at 70 degrF becomes
74.6 psi cold and at 118 degrF inside tire temp 88.6 psi
92.5psi/88.6 psi = 1.044 times more surface on ground gives 1.044^2= 1.09x more heatproduction.
So when colder tires rubber stays cooler then 300degrF when driving 99mph with maxload and reference-pressure on tire. So for safety not needed to fill up the cold pressure of 74.6 psi to 80 psi , with difference to hot temps, that you may do so for riding quality and fuell saving.
So I think the lists for filling higher at 70 degrF in a heated garage , to get the 80 psi in this example at for instance 20 degrF is because at those extreme cold ambiënt temperatures the deflection gets to much so for instance snake-bite.
Then its not anymore to prefent overheating, but for riding -quality.

[buddy110]

Good answers. I like to check in real temps (outside) However, the AM's are always cooler. Depending on the forecast (assuming it's getting warmer)I usually may leave them where they are if they are within low spec 3-4% of recommended inflation. A couple summers ago during the heat wave, my TPMS alarms went off. I needed to stop, bleed off some air as they were super high. So it all depends, and I routinely check my TP's as we travel

[jadatis]

And that is yust what you should not have done, that letting off air.

But it could mean that you need a higher cold pressure, but then borders of tmps must be set different, so you wont get the anoïng alarm.

And dont be afraid of to high pressure.
Once read that teststandards are, that new tires must stand a 2 to 3 times the referencepressure, ( that 80 psi for a E-load tire).

If you fill at 32 degrF ( freesing point) a 40% higher then reference-pressure ( so 112psi on a 80 psi), and incidentially temp in tire rises to 212 degrF ( boiling point of water at 14.7 psi ambiënt pressure), then pressure in tire rises to a small 2x the reference-pressure.

That is 160 psi.

You better worry about the temperature in tire, wich the pressure rising represents.
Using higher cold pressure then gives lesser deflection of tire, so lesser heatproduction.

The inside tire temp can incidenrially rise to that 212 degrF, when descending the mountains, and using the brakes to often.

[wolfe10]

Just raise all PSI's by 5-8 PSI sitting there in the climate control storage area.

[Gooma]

Check the tire pressure inside where it is more comfortable. Then go and don't worry about it. 20 or 30 degree temp difference won't make a noticable differene in tire pressure. If your anal about your pressures, dis regard this post.

[rvguy02]

Thanks everyone for your responses. Lot's to digest here, but I'm inclined to check pressure and add/bleed off as needed Saturday morning and not worry about it. In the past on chilly mornings (upper 40s during summer), I've noticed a 3-4 psi maximum drop. I did not worry about it much, especially because daytime temps were in the 70s and 80s. I also need to get off my a** and install the TPMS!

[rvguy02]

Originally Posted by Gooma

Check the tire pressure inside where it is more comfortable. Then go and don't worry about it. 20 or 30 degree temp difference won't make a noticable differene in tire pressure. If your anal about your pressures, dis regard this post.

Lol! Not anal fortunately... I tend to agree with your approach.

[wolfe10]

Originally Posted by rvguy02

I also need to get off my a** and install the TPMS!

A very good idea!

[alank]

Here's a thought, how many semi trucks do you see running up and down the roads, down to the coast and up over the mountains? How many times have you seen them adjusting their air pressure according to ambient air temp, altitude etc.

RVer's really overthink the tire pressure thing. I leave home with the proper pressure, travel west over 7000 ft elevation, sometimes 20* temps, and down into the Phoenix valley of warm weather. I then go home without touching the pressures until later in the summer if the TPMS indicates some attention is needed.

[jadatis]

And thats the right way to act, to my opinion.

If you then have tirefailure other then by punctures, its because the determined cold pressure is to low, and not because you let pressure swing with temperature.