Need help understanding Tire Pressure PSI Chart

Not to jump into the fray, but for what it's worth, the OP asked a very clear and simple question which was answered clearly in the first two responses. And the OP was happy. I believe others that may not be familiar with psi charts and the whole weighing your rig exercise also benefitted from the clear question and response.

When I first read the thread I thought good question, good response...but it won't stop here! Tire pressure threads seem to have a life of their own.

And apparently that's my contribution to the thread. :coolsmiley:

I agree, anything past post #6 does not add to the OP's question.
 
300 people have read this thread.
Only one of those people is the OP.
Threads are seldom about the OP alone.
If they were sorely about the OP;
no one would ever tell anyone to
Use the search engine.


The engineers get it within tolerable tolerance with a HUGE buffer on both sides.
Get comfortable, learn to LOOK at your tires, buy a $30 or $3000 tpms, learn what you like within parameters...
And. Like. It.
 
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I think my post #8 gave additional info.
Trew in the needed reserve, and why, and so higher pressure needed .

And gave answer about what cold pressure is , also a question of topicstarter.

The rest of my reactions where defending about the reserve,
 
300 people have read this thread.
Only one of those people is the OP.
Threads are seldom about the OP alone.
If they were sorely about the OP;
no one would ever tell anyone to
Use the search engine
.

Sure they would. How many unique problems and solutions do you see on this Forum?

How many times have the same problem and solution been re-hashed in multiple threads

Tire PSI is just one topic that a search would have answered the OP's question.
 
Absolutely...
Because...
The question is not unique to the op.
Thusly,
more information is needed to be added to the first few posts
Because...
Generic answers needed inserted to his specific
So as...
To fit the multitudes who'll read the thread.
Otherwise...
Someone with something different will Try to duplicate the exact information given to the op
Which might not...
Be anything but harmful to their situation.
So,
We can either say
Use the search engine
Or
We can elucidate and extrapolate to a point where the information might be
As
Broad as the audience
So as
Someone totally unknowing doesn't follow that chart to the very letter it seems to emphatically state.
 
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Didn't think my question would throw a hissy fit. I only ask my question because by adding 10 PSI to a cold rating of 82 PSI would give an operating temperature of around 100 PSI on the interstate. The ride quality at that pressure would be unbearable in a 30 foot Class A on an F53 chassis. I know that from experience. Ford's engineers and lawyers have more experience coming to a safety margin than any anonymous poster on an RV forum. I'll stick with the yellow sticker and my weight tickets from the local CAT scale.
 
To your question I answered with arguments why higher pressure is even needed to give maximum reserve, and still acceptable comfort and gripp.
The 82 psi then warm also higher pressure so lesser deflection, but I determined the 85% going from cold pressure, and still warm no discomfort.

So if my calculation comes to 90 psi in your situation, the higher pressure warm then still comfortable.

And its not the pressure alone, that blows a tire, its the weakened material by overheating that cources it.

A healty tire can stand a 2 times as much pressure as the here 110 psi referencepressure. These are teststandards.

To give you an idea, if 140% of referencepressure filled ( 110x 1.4= 154 psi at freesing point so 32 degr F. It rises to a small 220 psi at boilingpoint 212 degr F. , so yust within the teststandard..

So the normal pressure rising you dont need to worry about, its thevtemperature in tire it represents , and with that the temperature of tire-material you must worry about.
 
And?
Your point is what relative to a housewife driving an rv?
Where should the pressure be relative to the sticker on the wall, not as relative to laboratory testing? We don't care about, nor need confused about double the norms.

We're not here to be proven right by absolutes.
We're here to be proven valid by ranges dependent on prescribed values.
What's a valid range consistent with the wall sticker or makers sticker?

The members here are housewives and dentists and teachers and bankers.
The answer should be:

The wall sticker says xyz
Therefore
Do xyz+- only.


So, short form,
What's the answer for the +-variable?

Consider that my IQ might not break 100. Let's get kinda average guy and not so white smock guy.
What do I, an average 98 IQ guy too busy for a new psi based hobby, do about tire pressure on my generic rv?
 

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I will leave at this.
Gave in my first post all the answers topicstarters asked.
And He can use my list to get 105 psi front and rear, and 70 psi for the tag ( If tag).

Must be the language barriër , but this " pigheaded Dutch selfdeclared tyre-pressure specialist " a hobyist, cant follow your philosopical writing.

Gotta love the Duck. He can sometimes be very eloquent. Sometimes not. I’ll say this for the Op, I too experimented with that chart after weighing the unit with full water. Full gas. All our stuff. Except for spouse and dog. So my 16,000 GVWR chassis weighed in at 15,980. So adding my wife and dog adds 150 lbs. I’m a tad over. After comparing my 16,000 chassis/brake/drivetrain structure to knuckleheads 18000 GVWR chassis, mine is same size as his, frame, brakes, etc. my 245/70r19.5 Goodyears have minimum inflation of 80 psi. Which would’ve handled the weight. But the ride and handling was sloppy. So I played with psi until I got it where the handling was what I wanted. 90 psi front. 85 psi rear. Rides good. Handle good. A tad overweight. But that’s ok
 
Poetic Justice

Edumadation is often worn as a badge of riteousness.
It is indeed often just an Irish pennant used as a guidon.
Specific pride overrides the dignity of extrapolation.


You can lead a horse to logic
But you can't make it think.

It's a tire.
There is no need for math.

I wrote of hobbyists.
Guess who isn't

Ducksface, I have always enjoyed your voice of experience, and now I see you have a bit of the Irish Poet in you. Information is good, entertaining information is even better! Looking forward to your next chime in.
 
Confusion

If the OP was confused before he must really be scratching his head after reading this:

The conclusions you took are all right.
Mayby wrong about the single/duallload thing.

But you forget to build in a reserve.
Needed for next:
Unequal weight R/L on the axle .
Inacurate reading of pressure and weight.
Pressure loss in time.
Going over 75 mph for your tires

When I make a cold pressure axleload list I make them for a bit virtuall higher speed, for your tires for instance 87 mph ( not saying you must drive that) and give 90% of calculated axleloadcapacity for the cold pressure.
This then still. Gives acceptable comfort and gripp, so I concluded from reactions.

Then you dont need to do pre or after calculations yourselves.

Then you " only" have to determine the axleloads (better would have been axle-end loads) 99% accurate, wich you did by weighing.
But did you weigh fully loaded?
This determining axle(end) loads accurate in your use, is your responcibility.

I assume the trailerweight on the weightslip is the tag axle, but correct me if wrong. Then same tires.

And you have the top tires in the list so maxload S 3970 lbs / D 3750 lbs. At 110 psi , but also correct me if wrong.

I estimate pressures determined with use of my made list will come to about 100 psi, and still acceptable comfort and gripp.


Then about what cold pressure is.


Best definition is when temperature of gascompound in tire is practically the same as the outside ambiënt temperature.

That is when not driven long enaugh and no external factors, like sunshine on tire.
This last has become the definition .

Now there are 2 camps in if recomended cold pressure is for a certain ambiënt temperature.

Camp 1 is largest, and states that you have to fill the determined needed cold pressure at any ambiënt temperature , be it 20 degr F or 110 degr F . Gives you a chalance to fill up and blead down when traveling trough extreme ambiënt temperature regions.

I am in the second smaller camp, that states that determined needed cold pressure or recomended is for an index temperature given
Read index temperatures ( As RIMEX cals it) between 60 degr F/ 15bdegr C upto 77 degr F / 25 degr C .
Mostly 20 degr C / 68 degr F.

Porche and BMW give on tmps screen besides the pressure also the recomended pressure calculated from index temp ( most likely 68 degr F) to the temperature in tire ( also sent by the sensors) . Some tmps systems for motorcicles give on screen pressure calculated back to 20 degr C / 68 degr F.

A tmps system is yust a little computer in wich the designing ingenieur can put software he thinks needed.

This then can give differences between tmps reading and gauge-reading.

My opinion based on conclusions I took in time is that you can let the pressure flow with temperature change.

When hot the higher pressure gives lesser deflection, so heatproduction at same speed, wich compensates the lesser cooling down by lesser temperature differences between tire-material and in-and out-side tire air ( or other gascompound) .
So never blead down cold or warm pressure on a hot day.


When cold ambiënt the other way around.
More heatproduction and more cooling down.

But then you may highen up to determined needed for reasons of riding quality and fuell saving, but not needed for savety of tire, so no overheating tire-material, wich is main goal of tiremakers when determining needed pressure.

If the camp 2ers are right, you only have to check if pressure and temperature are in line, and dont need to fill up and blead down maniacally.

Tmps systems give a direct warning when pressure drops 2 psi .
 
Since this thread has started, I have removed all of my Goodyear G670 RV 24070R/19.5 tires and threw away my Goodyear Tire chart as worthless. I am sure they are good tires for somebody. I can't wait to see the actual interstate difference if any with my new tires for pressure and temperature.

I can say the newer tires ride smoother and not as chunky / bumpy around town.
 
I start out at 82 psi cold. In just a few miles I am up to 90 to 95 depending on outside temps. After some high speed on a hot day it's 99-102 on the rears and maybe a couple less on the fronts. At those temps the load carrying capacity has increased quite a bit. No need to be adding more cold. It would just push the highway pressures even higher and make the ride more harsh. Flawed logic?
 
I start out at 82 psi cold. In just a few miles I am up to 90 to 95 depending on outside temps. After some high speed on a hot day it's 99-102 on the rears and maybe a couple less on the fronts. At those temps the load carrying capacity has increased quite a bit. No need to be adding more cold. It would just push the highway pressures even higher and make the ride more harsh. Flawed logic?

Yes, tire load capacity is based on COLD tire pressure. Tire heating and resultant pressure increases are already taken into account.
 
Yes, tire load capacity is based on COLD tire pressure. Tire heating and resultant pressure increases are already taken into account.
Yes. That is my point. If the tire pressure increases due to heating while traveling, it also increases the load carrying capacity of the tire because of the additional pressure. So adding another 10 psi cold for "insurance" is overkill.

Looking at it another way, if I have 95 psi in my tire because of the tire heating up while driving, do I not have the same load carrying capacity of a cold tire inflated to 95 psi?
 
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No warm higher pressure does not increase the loadcapacity. The cold pressure is so determined, that warm it gets a deflection that wont overheat the tire.

Tirepressure advice is all to give the tire a deflection warm , so heatproduction per cycle , that wont overheat any part of tire-material, driving the speed constantly ,for wich it is determined.

That is main goal of tiremakers, other things also important, but this is main goal.

So if driving higher speed, needs higher pressure for same load, to give lesser deflection, so heatproduction a cycle, times more cycles a second still gives same heatproduction a second. Cooling down of tire-material stays practically the same regardles of speed.

On european trucktires almost always additional service descriptions given , official term, is other loadindex/ maxload for other speed . See picture I made a few years ago in my vilage. Also see the DOT code with production date about 10 years old.

Again all to not overheat any part of tire-material .
 

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No warm higher pressure does not increase the loadcapacity. The cold pressure is so determined, that warm it gets a deflection that wont overheat the tire.

Tirepressure advice is all to give the tire a deflection warm , so heatproduction per cycle , that wont overheat any part of tire-material, driving the speed constantly ,for wich it is determined.

That is main goal of tiremakers, other things also important, but this is main goal.

So if driving higher speed, needs higher pressure for same load, to give lesser deflection, so heatproduction a cycle, times more cycles a second still gives same heatproduction a second. Cooling down of tire-material stays practically the same regardles of speed.

On european trucktires almost always additional service descriptions given , official term, is other loadindex/ maxload for other speed . See picture I made a few years ago in my vilage. Also see the DOT code with production date about 10 years old.

Again all to not overheat any part of tire-material .

I think what you said is important, but you are not speaking to a convention group full of Ford, Firestone, Michelin, or Goodyear Tire Engineers. Can you make it make sense for a RV owner? The legalnese is in part why many struggle with, misuse, or simply don't use the Tire Charts.

I run 82 psi cold 100% of the time, check cold pressure before every trip using a $40 TPMS system and now a $1,200 TPMS system running on arguably the most expensive tires money can buy. I had two blowouts not hitting anything, and neither of TPMS systems said anything until well after the flat.

Further, with my expensive TPMS I can watch psi and temperature increases to damn near go off the charts. RV parked and tires not moving just the Texas sun. Yesterday I went from 83 degrees in the morning to 104 degrees on one tire just sitting.

While I am beating this drum, none of the TPMS Mfgs can give you straight talk about upper and lower settings to which to have the TPMS alarms trigger. Just mumbo jumbo that at the end of day may be to try 20 psi higher and see what happens.

Not for you, but perhaps why this topic never dies; because no one has the real answers. After 4 1/2 years of following the experts advise and verifying my pressures and weights which is all I can control and still having 2 blowouts, I am gonna try something different. Like a better rated tire than what Ford Engineering & Goodyear spec'd out & recommend for my chassis. Everything else will be the exact same. I hope 4 years from now, I have zero blowouts to reports.
 
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School often fills a void the schooled have.

Mark Twain(ish)
I have never let my schooling get in the way of my education.

It's.
Just.
Tires.

Rv's are nothing special
We as a group are nothing special

Airlines and the space shuttle delivery vehicle don't put as much emphasis on something this so mundane as tires.



"Tire Blowout Statistics
Approximately 33,000 tire-related vehicle accidents occur each year on average, leading to nearly 20,000 injuries. In 2020, accidents attributed to tire failure caused more than 600 fatalities."

Above is The biggest possible lie a legal team could get away with without losing their jobs for flagrancy.

600 deaths.
More people were killed slipping on wet surfaces.
Let's talk of shoe sole durometers.
 
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