Tire pressure

[John1949]

I hope this is the right category. I am a little concerned about trailer tire pressure. ST tire is marked 65 lbs max cold. Are these ratings designed to take increased pressure after warmup into account?

[Mike134]

Short answer yes.

What does the label on the trailer say to use as a starting PSI?

[John1949]

65

[NavyLCDR]

The pressure specified both on the tire itself and on the label on the trailer are cold pressures. Cold is defined as not driven or in directly sunlight for 2 hours. The tire and wheels are designed to handle the pressure increase due to changes in temperature and altitude while traveling.

The tires on my Dodge Durango go from 38 PSI to 44 PSI on the TPMS from cold to interstate towing. I don't have TPMS on the trailer yet, but with the tires being much smaller I would expect the pressure to probably go from 65 PSI cold to maybe 80 PSI on the highway. But the manufacturers allow for the increase.

[John1949]

Thanks for the info.

[phillyg]

Max cold pressure is the maximum you should ever air the tires before they're driven on. The tire mfgr. has taken into consideration that the tire will heat up during use.

[jadatis]

Its all a bit more complicated.

Cold pressure is when in and outside the tire the gascompound has the same temperature, that simple, and that is when not driven long enaugh, and no external factors like sunshine on tire.


The 65 psi is cold pressure to fill to carry the maximum load for the reference speed.
For normal P-tires this referencespeed is 160kmph/99mph even For V speedrated is max speed 149mph. And for ST always 65mph, also the Endurance with N speedrating is max 140kmph/87mph.

Tires are designed to stand a 2 to 3 times the referencepressure (your 65 psi, so something between 130 and 195 psi !!!!!!)

Pressure advice is to give the tire when driving the speed its calculated for constantly ( not totally true) a deflection warm , that wont overheat any part of rubber of tire.
The gascompound in tire can get incidentially even 100degrC/212 degrF. For instance when descending from the mountains, and using the brakes to often, but with that higher pressure so lesser heatproduction a cycle, and lower speed used, so lesser cycles a second, so most likely the rubber wont reach the critical temp, at wich it hardens, and beginning crackes are made wich dont disapear.
Warm pressure is inacurate to determine, howmuch has it warmed up by driving and howmuch has it cooled down after you stopped, and first tanked fi.
Cold is more certain, fot that reason cold is used.

If that happens in fact the tire is lost then, but it can take years before that much further cracked that tire blows.

So dont be afraid if pressure goes above 65 psi, and dont lower it then, gives more deflection
So heatproduction, then the cooling down can handle, so critical temp of rubber is sooner reached.

Will leave it at this ...for now. Absorbe this first, then you look different at that relatively little higher pressure warm.

On a hot summermorning , you better fill a vew psi higher then your 65 psi, because cooling down of rubber is less then , because of lesser tempdifference between rubber and in- and out- side tire gascompound.

Why that anoing gascompound? Nitrogen filling is other gascompound then air, 95% nitrogen instead of 78%.

[NavyLCDR]

Originally Posted by jadatis

Its all a bit more complicated.

But it doesn't have to be. Just inflate the tires to the specified pressure when they have not been driven on the last 2 hours and when they have been shaded (not in direct sunlight) for two hours. That's as complicated as it needs to be.

[Mike134]

Originally Posted by NavyLCDR

But it doesn't have to be. Just inflate the tires to the specified pressure when they have not been driven on the last 2 hours and when they have been shaded (not in direct sunlight) for two hours. That's as complicated as it needs to be.

X2!!

[jadatis]

Made you a nice pressure/temperature list for 65 psi cold advice pressure.
External TMPS-sensors give temperature pretty accurate, but its from the air at the end of the valve, and not of inside tire, so temp of them is worthles. With this list you can get the real temp in tire at the read pressure from tmps, wich is more acurate. Can make such a list for every pressure and steps ( here 1 psi used as step)
F. / PSI
32 / 60
39 / 61
45 / 62
52 / 63
58 / 64
65 / 65 advice-pressure
72 / 66
78 / 67
85 / 68
91 / 69
98 / 70
105 / 71
111 / 72
118 / 73
124 / 74
131 / 75
137 / 76
144 / 77
151 / 78
157 / 79
F. / PSI

[phillyg]

Jadatis, what the heck is wrong with you, trying to overwhelm us noobs with facts?

[jadatis]

Yes I like to do that
But things like when not driven for 2 hours, can be understood better if you know why.

Another one, " never blead air from a hot tire" is not so you wont burn your fingers, its because the tire needs the higher pressure to give lesser deflection, so heatproduction. Once you understand why, you can forget it, and act as is needed.

But I realise that you have to read it 3 times to understand it.

[Mike134]

Originally Posted by jadatis

Yes I like to do that


But I realise <spelling is wrong, if you're going to get snarky at least show some spelling skills> that you have to read it 3 times to understand it.

I've met you in my life's travels. you fall into one of the following, "If you can't dazzle em with brilliance, buffalo them with BS."

You seem to think your smart lets see if you can figure out which one you are.

[Airdale]

Originally Posted by Mike134

I've met you in my life's travels. you fall into one of the following, "If you can't dazzle em with brilliance, buffalo them with BS."

You seem to think your smart lets see if you can figure out which one you are.

Jadatis is in Holland. He is probably a tire engineer but not familiar with USA DOT regulations of any kind.

Most of us don't give a hoot about tire construction as long as it's past the testing for the DOT emblem on it's sidewall. Besides that, most of the materials used in tread and sidewall constructions are confidential.

[ARhappycamper]

Ah Heck ! If the tire says 65 psi, put in 65 psi !!! Nothing is going to ignite or self destruct !

[jadatis]

Originally Posted by Airdale

Jadatis is in Holland. He is probably a tire engineer but not familiar with USA DOT regulations of any kind.

Most of us don't give a hoot about tire construction as long as it's past the testing for the DOT emblem on it's sidewall. Besides that, most of the materials used in tread and sidewall constructions are confidential.

I am not even a tire-specialist, worked as optician-contactlens-specialist, but for 6 years now in logistics. Think I was to pigheaded for optics too,and no comercial attitude, so in the end no one wanted me anymore.

Always had an interest in math, and think many subjects can be solved with math.

That I misspell and use wrong words is because I dont use every time google translate, but people will understand what I mean.
Also mistypings, because I do it all on mobile phone, askes much of fine motorics of this 61 year old man.

[John1949]

Great info, thanks!

[Lins]

Originally Posted by NavyLCDR

But it doesn't have to be. Just inflate the tires to the specified pressure when they have not been driven on the last 2 hours and when they have been shaded (not in direct sunlight) for two hours. That's as complicated as it needs to be.

X3

[Toy4Rick]

I read a post somewhere that indicated the PSI listed is when the rig is fully loaded to max weight... and that a 4 point weight should be done then adjust down accordingly. IOW, if max load weight is not reached, then max PSI shouldn't be used

Here is why I ask, my 2021 24' Sunseeker on a Ford E-450 chassis and the FR label both show PSI at 75F/80R and since I don't travel at max load weight...

Should I stick with 75/80 as labeled?

[Lins]

Originally Posted by Toy4Rick

I read a post somewhere that indicated the PSI listed is when the rig is fully loaded to max weight... and that a 4 point weight should be done then adjust down accordingly. IOW, if max load weight is not reached, then max PSI shouldn't be used

Here is why I ask, my 2021 24' Sunseeker on a Ford E-450 chassis and the FR label both show PSI at 75F/80R and since I don't travel at max load weight...

Should I stick with 75/80 as labeled?

Unless you are SIGNIFICANTLY below max weight I would stick to the proper pressure.