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Old 11-01-2021, 09:35 AM   #127
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Option 1: Follow manufacturer recommended guidance for tire inflation.

Option 2: Spend hours compiling useless information.
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Old 11-01-2021, 09:42 AM   #128
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Originally Posted by jadatis View Post
Made my ( to) long story about why I think pressure as to be higher cold at 100degrF then at 70 degrF.



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 ambiŽnt 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 ď spagetty-strings" slide over each other.



Tires are vulcanised at the end, and this makes sulfurbridges between the ď spagetti ď 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 ambiŽnt 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 ambiŽnt 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 ambiŽnt temperature 390degrF worth of cooling capacity.

At 100degrF ambiŽnt 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 ambiŽnt 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 ambiŽnt temperature to 80psi, as is stated to be allowed because cold filled is at ambiŽnt 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 ambiŽnt 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 ambiŽnt temperatures the deflection gets to much so for instance snake-bite.

Then its not anymore to prefent overheating, but for riding -quality.


I appreciate your effort to give a writeup of your thinking ... but there unfortunately is a lot of things that are incorrect in this.

First is the assumption that temperature is the *only* thing that degrades tires. This is not the case. Tires are not only rubber ... they also have steel plys encased in the rubber. Excess flexing (like when the tire is low on pressure) stresses the materials at the boundaries between steel and rubber, and decreases the "bond" between them, thus weakening the tire. This is more a mechanical thing than a thermal thing.

Second, your analysis seems to rely on an assumption that either part of the tire must be running at vulcanization temperatures, and that reaching vulcanization temperatures is necessary to create damage to the tire. Both of these are incorrect. Vulcanization temperatures are HOT. if a tire reached those temps, you would be seeing smoke. Tires just dont get that hot. Also, thermal damage (which is not just damage to the sulfer bridges, but actually is mostly damage/breaking of the "strings" between the sulfer bridges) occurs at any temperature, but is accellerated more as temperatures go up. There is no "magic" temperature where damage starts ... but the hotter they get the more damage is done.

I think you are partially correct in that at low ambient temperatures the risk of thermal damage is reduced, but if the tire is underinflated, you still have increased flexure, and thus greatly increased risk of strictly mechanical damage.

Thank you again for your efforts to get your thoughts put down in writing.
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Old 11-02-2021, 04:19 AM   #129
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Answer to post #128 right above.

I used the maxload and that vulcanisation temp as extreme example so most likely overheating kind of problems begin at lower rubber temp.

Firs used 280degrF as highest allowed rubber temp, but gave even more difference between heating up and cooling down.

And luckyly we dont drive 99mph with RV , wich keep the tires rubber cooler.

But ST is calculated in maxload so driving 65mph with maxload and reference-pressure, gives that 300degrF ( if thats the critical temp) , the more deflection then is not yet seen as a problem.

But thebpoint I am making is that especially at high AmbiŽnt temperature, you must not fill 80 psi( if determined needed) but higher, and thats the discussion here.
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Old 11-02-2021, 08:20 AM   #130
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Originally Posted by jadatis View Post
Answer to post #128 right above.

I used the maxload and that vulcanisation temp as extreme example so most likely overheating kind of problems begin at lower rubber temp.

Firs used 280degrF as highest allowed rubber temp, but gave even more difference between heating up and cooling down.

And luckyly we dont drive 99mph with RV , wich keep the tires rubber cooler.

But ST is calculated in maxload so driving 65mph with maxload and reference-pressure, gives that 300degrF ( if thats the critical temp) , the more deflection then is not yet seen as a problem.

But thebpoint I am making is that especially at high AmbiŽnt temperature, you must not fill 80 psi( if determined needed) but higher, and thats the discussion here.
What qualifications do you have to make recommendations other than those provided by the tire manufacturers?
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Old 11-02-2021, 09:02 AM   #131
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Answer to post #130.

I am yust an amateur in this.
If you follow the official accepted rule of filling fi80 psi if determined right, at ambiŽnt temperature, next can happen.

You leave at a hot morning of 90 degrF , and give tires 80psi cold pressure.
Then driving higher speed, the tires then overheat, to my conclusions.

And that may only happen ZERO times in tires live.
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Old 11-02-2021, 09:49 AM   #132
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Jadatis - i dont know if this will do any good, but will try. I have to admit that i have a little trouble understanding you analysis (due to the english translation), but i have tried, and i *think* i understand what you are trying to say. And ... i am afraid your analysis is very flawed.

First, your assessment that heat is lost from the tire directly from the tire to the ambient as well as through the rim (which is correct) is an *additive* "heat loss factor" is incorrect. The processes act in parallel (not additive). There is more wrong with these sets of assumptions regarding how heat is transferred out of the tire, but lets leave it at that.

The second thing i spot is that your assumption of a certain temperature internal to the tire is mathematically flawed. This is not a class on differential equations so i wont go into detail ... but leave it at the statement thatyou do *not* go about understanding a system like this by assuming some internal temperature. In this case doing do has led you to a conclusion that is dangerously wrong.

I applaud you for trying to think about this logically in terms of heat generation and loss of that heat to the ambient, but the approach you have taken is incorrect and misleading

Someone asked your credentials. I will give you mine, so hopefully you are less likely to just dismiss what i said above. I have a PhD in chemical engineering ... with much of my focus (in training and in my career) on heat transport, and very high end computer analysis of heat transport.
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Old 11-02-2021, 09:52 AM   #133
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I find it amazing that so much can be said about attaining the correct tire pressure. It's such a simple process. Either inflate to the placard pressure and don't overload the axles, or weigh the wheel positions and inflate according to the load inflation tables, (keeping all tires on an axle equal) that the tire manufacturer has tested to be a safe level. It doesn't get any simpler than that.
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Old 11-02-2021, 09:55 AM   #134
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I find it amazing that so much can be said about attaining the correct tire pressure. It's such a simple process. Either inflate to the placard pressure and don't overload the axles, or weigh the wheel positions and inflate according to the load inflation tables, (keeping all tires on an axle equal) that the tire manufacturer has tested to be a safe level. It doesn't get any simpler than that.
Could not agree more.
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Old 11-02-2021, 10:39 AM   #135
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I find it amazing that so much can be said about attaining the correct tire pressure. It's such a simple process. Either inflate to the placard pressure and don't overload the axles, or weigh the wheel positions and inflate according to the load inflation tables, (keeping all tires on an axle equal) that the tire manufacturer has tested to be a safe level. It doesn't get any simpler than that.


Why take a simple approach when you can complicate things beyond all recognition?

(For the record, i weigh, add 10%, and use the same pressure on both sides of an axel)
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Old 11-02-2021, 01:07 PM   #136
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I recently noticed my cold pressure has decreased in all tires (by TPMS) by almost 7 pounds in the mornings with temps in the 40's. But within 10 driving miles they are back to normal pressure.
My question is, should I add more air at cold ambient temps to bring pressure to cold normal settings?
I quoted the original question, to show that this topic is all about , what to do at cold ambiŽnt temperature.
My conclusion is do nothing, but more impotant is that you dont lower pressure at high ambiŽnt temperature.

Its important to determine the needed pressure with reserve, but that is not the question in this topic.

But my idea is that 2ce as much temperature-difference gives 2ce as much cooling down. Am I wrong in that.
And in the end all the heat is transported to the outside air, the rimm is only a 2nd barriŽre.
For this reason it would not be wise to make rimms of Carbon. Does not transport the heat as good as iron or alloy.
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Old 11-02-2021, 02:17 PM   #137
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MN-Traveler wrote " Vulcanization temperatures are HOT. if a tire reached those temps, you would be seeing smoke.

Tried it out.
Own a electric paint-stripper wich you can read and tune the temperature.
Took an inner tire of bicicle, and began at 170 degrC= 338 degrF, and heated the tire at one spot,
Became a bit whitisch but stil flexable afterward.

So at 190 degrF , nothing , took larger steps
At 300 degrF/572 degrF still nothing happened, and inpatiantly went direct to 400grC/ 752 degrF, and YES , a bit smoke and smell , and rubberbubbled up and surface harder and afterward cracks. Made picture of it.

But still I think the 170 degrC/ 338 degrF must not be reached. Mayby 130 degrC= 266degrF is not good for the tire.
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Old 11-02-2021, 03:30 PM   #138
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MN-Traveler wrote " Vulcanization temperatures are HOT. if a tire reached those temps, you would be seeing smoke.

Tried it out.
Own a electric paint-stripper wich you can read and tune the temperature.
Took an inner tire of bicicle, and began at 170 degrC= 338 degrF, and heated the tire at one spot,
Became a bit whitisch but stil flexable afterward.

So at 190 degrF , nothing , took larger steps
At 300 degrF/572 degrF still nothing happened, and inpatiantly went direct to 400grC/ 752 degrF, and YES , a bit smoke and smell , and rubberbubbled up and surface harder and afterward cracks. Made picture of it.

But still I think the 170 degrC/ 338 degrF must not be reached. Mayby 130 degrC= 266degrF is not good for the tire.
Have you ever asked your buddy at Vredestein what the highest temperature is that heís ever seen on a tire? Specifically, one operated within the stated load and speed ratings.

All this stuff has been figured out, by professionals.

Follow their recommendations. Itís pointless to keep trying to reinvent the wheel.

Engineers on this forum have repeatedly mentioned the flaws in your theories. Will you ever heed their advice?
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Old 11-02-2021, 06:12 PM   #139
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Jadatis - one final, not quite so delicate, attempt to sway you from your theory. Here in Minnesota it is getting colder. Just today, the "Low Tire" pressure warning went off in my car. Not because the tire lost air, but because the pressure is getting lower because the temperature is getting colder (all of the tires are showing lower pressures). IF your theory is valid, then please explain to all of us here why, many, many VERY smart scientists and engineers have not designed the pressure sensors that are nowadays installed in almost every car manufactured to .... correct for temperature and NOT issue a "low tire" warning just because the temperature has gone down????? The reason is because your theories are not only just plain wrong, they are uninformed and DANGEROUSLY wrong.

To all others reading this thread - please think very carefully before you give credence to the theories and advice offered on this subject by Jadatis.
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Old 11-02-2021, 06:25 PM   #140
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My normal cold pressure by my weights is 105 all around my Horizon.
I left Pennsylvania last December 26th my pressure was 99
Kept my speed at about 55-60 on the interstate until I got to 103 and then picked up to 65. By the time I got to Virginia I was running 115 and tire temps were normal all the way. By the time I got to Florida I was running 120
Never put air in or took it out.
Drove back north and by the time I got home I was running 105.
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