Max tire pressure

Once read from Tireman9 or Capriracer , that tires have teststandards, so they have to stand a pressure of 2 to 3 times the pressure behind AT.
So your 80 psi can rise to 160 to 240 psi before they blow.
I would not try this at home, if tire is already damaged by using to low pressure once, so overheating has happened long enaugh, it will blow sooner.
But gives an idea that only for the tires, you dont have to be affaid of putting for instance 120 psi in it ,if its undamaged.


In old PDF I have from Semperit ( Continental Group) they prescribe 140% of that pressure behind AT( official reference-pressure, but will call it AT-pressure furtheron). Then the tire is allowed 2 times the maximum load when speed zero so standing still.

Continental group in Europe gives on many tires 2 pressures.
1. The pressure behind AT but without AT in front of it right behind the service-descriptions ( example 255/70R16 121/119R 65psi)
2 on the other side behind the maxload information "maximum inflation pressure of 10 psi higher then 1 (so then 75 psi).
, and this is also cold pressure .

Also old documents of Goodyear gave for ST tires a 10psi higher pressure for 75mph.

Nowadays, if not given on tire-sidewall, you may not fill cold pressure higher then AT-pressure.
In earlyer days it was allowed.

Cold pressure is when inside tire airtemp is outside/ambiënt temp, that simple.
But sun can heat up the tire inside even when standing still.
Also exaust pipe yust in front of rearwheel can make that tire hotter .
Cold pressure advice and also AT-pressure is meanth for 18or20degrC/65or68degrF.
So you can always argue when filled fi 90 psi on AT80psi tire, that you filled it at freesing point( 0degrC/32degrF), and the pressure has rissen to that 90 psi now its 65 degr F.

Suppose you fill at freesing point of 32 degr F your tires with 1,4 times the AT-pressure , and in use the temp in tire goes to boiling point of water so 212 degr F, Then the pressure in tire will rise to a small 2x AT-pressure , so still within the test-standards of 2 to 3 times AT. Boiling point of water it can incidentially get in the tire, when descending the mountains and using the brakes to often.
Then heat of brakes is transported trough the rimms to the tire inside.

I suspect tiremakers to sometimes fi put a D-load designed tire( AT 65 psi) in the market as E-load ( AT 80 psi) , because especially american market asks for it.
But then the 2 to 3 times higher then AT wont go anymore.
Mayby thats the reason why they standard dont allow higher then AT-pressure anymore.

For P- tires , only maximum cold pressure is given on sidewall, of 44 to 51 psi , and for XL sometimes even 60psi.
The AT-pressure of a standardload P-tire is USA system 35 psi always, and EUR system 36 psi with exeptions to lower.
XL/reinforced/EXtraload USA 41psi always, EUR 42psi with exeptions to higher and lower.
So for P- tires its normal standard to allow higher cold pressure then AT.

In November, we drove a car up to Michigan for Thanksgiving (cold PSI was normal when we left). The temps got down into the negative teens. The low air pressure warning came on so I filled them to the cold level which was 44PSI. When we got back down to Southwest Florida, the cold PSI was 65 PSI. I guess you can add to the discussion...also depends on the ambient air temperature also.

Ken

I've seen my 16" load E tires 80 psi cold set run 92-94 psi on my loaded equipment trailer on long all day runs in 100-110 degree outside temps.
Out of habit when I pulled for a living I still thump truck and trailer tires each morning before drive away and at each fuel/potty stop when making long trips.

First it does not say MAX 80 PSI Cold... It says Maximum Load XXXX at max pressure of 80 PSI cold (Cold is about 72 degrees but do nto sweat that too much) and that means what it says.. 80 PSI at any temp you are likely to be checking the pressure at first thing in the AM after at least 8 hours of PARKED.

What the pressure is when going down the highway (USE a remote reading TPMS to check at 55 MPH) Well note the pressure on all tires.. if ONE is way higher than the rest you have a problem (likely a dragging brake or a bad bearing in that order) but else do not worry.

Likewise if one is LOWER than the rest (Leak).

steelhunter wrote:
It means 80psi cold maximum. Period. Exactly what it says.

Tires warm when driving thus increasing the pressure. This is normal.

Don't worry about this increase in pressure and DON'T ever bleed off a hot tire unless you have a death wish.

I actually saw a guy doing this to his 5th wheel at a rest stop. He told me he had to keep the pressure 80 psi or less.

It’s good to get your rig weighed. TV, trailer, motor home, front and rear tire weights. Then you can refer to the tire manufacturers specs for pressures to run.

Don't overthink this. 80 psi cold means before the tires have been used. Check before you drive and you'll be good. My 110 psi will hit 120+ psi when it's hot, but I rarely run them at the pressure.

steelhunter wrote:
It means 80psi cold maximum. Period. Exactly what it says.

Tires warm when driving thus increasing the pressure. This is normal.

Don't worry about this increase in pressure and DON'T ever bleed off a hot tire unless you have a death wish.

Further to this point, be careful if you take your motorhome to one of the 10 minute oil change places. I've caught countless "tire jockeys" at these places doing just that, bleeding air from warm/hot tires, to get them down to the door frame's suggested tire pressures. The first time this happened to me, I noticed the tires looked a little soft the morning after an oil change. I realized the tire guy had bled them down to what he thought was supposed to be the correct pressure. I was about 8 psi low per tire, below what I normally run them at. I now warn them "no tire service, please and thank you". If they ask why, I tell them, and their eyes usually "saucer up" appropriately.

tarnold wrote:
Playing off my other post, if a tire says “max cold pressure 80psi,” what can you safely run that tire at? If you already run this at 80psi cold and other post shows up to 25% increase in psi at high road temps your bumping 100psi. Ok or not?

If you filled to 80psi cold (before driven, before the sun is on them) the tires are good all day in all conditions. Temperature and pressure changes due to speed, heat, elevation and weather are all accounted for.

If your climate does change significantly then by all means check the pressure the next morning to verify you again start at 80 psi cold.

steelhunter wrote:
It means 80psi cold maximum. Period. Exactly what it says.

Tires warm when driving thus increasing the pressure. This is normal.

Don't worry about this increase in pressure and DON'T ever bleed off a hot tire unless you have a death wish.

ABSOLUTELY CORRECT!

And "cold" is at current ambient temperature, NOT at a specific temperature.