PSI, PSI, PSI...is there a consensus??

[lestahhh]

Hey everyone, it's me the newbie again. I'd like to get input on something I've been researching and it seems I can't find any agreement on what psi tires should have! One side of the coin strongly swears ST tires should be inflated to max psi cold stated on sidewalls. Other side says it should be proportionate to load as posted on tire manufacturer charts. Well, which is it?!

I have Goodride tires ST225/75r15e, and my weight is approx 7700#, it's a TT with 2 axles. (These tires came with trailer, previous owner upgraded tires and wheels from manufacturer -- I will upgrade brand in upcoming weeks).

Logic tells me inflating tires to the max they hold is dangerous bc it doesn't allow room for hot air!

Today, I had a mobile tire company come and exchange one of my tires because Monday I got a nail so I had to use my spare, which is an extra tire and not a donut. (if trailers even use donuts!). Anyways, so I asked one of the two guys what psi did he inflate it to and he said he always goes to the posted max! So he said 60. I corrected him that the posted psi for mine is 80 so he told the other guy to inflate it up while he took payment. So I went to the other guy and asked him what he thinks the tire should be inflated to and he said based on my load and for the size of tire it should be 65 psi. I asked both of them for source on their info and they pretty much said it's based on experience. So I said ok. But this illustrates my frustration! Two tire guys with contrasting opinions!

To add to this, the previous owner had these tires to 65. He said based on his research that's what it should be. I didn't question him and haven't had any issues. So I refer to yll for some feedback, please.

Thank you.

[flybouy]

Pretty simple really. Look at the placard on the front roadside of the trailer. It will list the minimum tire size, rating, and inflation. So let's say the O.E.M. tires have a D weight rating and 65 psi. That's the correct psi to get the rated weight carring capacity of the tire. Now if you upgrade to an E rated tire then you need to inflate it to 80 psi if you want the benefit of the extra capacity.

As for "hot air" all vehichle tires are rated to safely handle the increase in air pressure due to ambient temps or normal road friction. And no, there's no such thing as a compact spare for trailers nor is there a need for it.

[lestahhh]

Originally Posted by flybouy

Pretty simple really. Look at the placard on the front roadside of the trailer. It will list the minimum tire size, rating, and inflation. So let's say the O.E.M. tires have a D weight rating and 65 psi. That's the correct psi to get the rated weight carring capacity of the tire. Now if you upgrade to an E rated tire then you need to inflate it to 80 psi if you want the benefit of the extra capacity.

As for "hot air" all vehichle tires are rated to safely handle the increase in air pressure due to ambient temps or normal road friction. And no, there's no such thing as a compact spare for trailers nor is there a need for it.

Thank you for your quick reply and clarifying about the hot air and donuts! My placard does say this same size tires and same thing about max psi cold 80.

[JRTJH]

Originally Posted by lestahhh

Hey everyone, it's me the newbie again. I'd like to get input on something I've been researching and it seems I can't find any agreement on what psi tires should have! One side of the coin strongly swears ST tires should be inflated to max psi cold stated on sidewalls. Other side says it should be proportionate to load as posted on tire manufacturer charts. Well, which is it?!

I have Goodride tires ST225/75r15e, and my weight is approx 7700#, it's a TT with 2 axles. (These tires came with trailer, previous owner upgraded tires and wheels from manufacturer -- I will upgrade brand in upcoming weeks).

Logic tells me inflating tires to the max they hold is dangerous bc it doesn't allow room for hot air!

Today, I had a mobile tire company come and exchange one of my tires because Monday I got a nail so I had to use my spare, which is an extra tire and not a donut. (if trailers even use donuts!). Anyways, so I asked one of the two guys what psi did he inflate it to and he said he always goes to the posted max! So he said 60. I corrected him that the posted psi for mine is 80 so he told the other guy to inflate it up while he took payment. So I went to the other guy and asked him what he thinks the tire should be inflated to and he said based on my load and for the size of tire it should be 65 psi. I asked both of them for source on their info and they pretty much said it's based on experience. So I said ok. But this illustrates my frustration! Two tire guys with contrasting opinions!

To add to this, the previous owner had these tires to 65. He said based on his research that's what it should be. I didn't question him and haven't had any issues. So I refer to yll for some feedback, please.

Thank you.

OK, let's do a little "observing"... First, two guys show up to change out a tire, they NEVER weight your trailer, but somehow can "devine" that the placard on your trailer is wrong (80 PSI cold inflation pressure) and their "experience" indicates that you should actually be running either 60PSI or 65PSI based on their assessment (without knowing actual weight of the trailer)..... And their "vast knowledge of trailer tires" supposedly outweighs the automotive and mechanical engineering knowledge that went into designing, testing and building the trailer ?????

Methinks you've been "duped by a couple of cowboys with a tire iron"......

Follow the recommendation from the trailer manufacturer. It's located on the tire placard on the front roadside corner of the trailer.....

Did either of those guys wear his baseball cap "crooked on his head" ??? If so, chances are the appendage on his shoulders was a better hat rack than a cranial storage facility.....

[travelin texans]

Every time I had tires repaired or replaced at any tire shop regardless of tire size or what they were mounted on they've inflated them to 32-35 psi even on my duallies. So much for the experts!
IMHO inflate to the rv recommended inflation on the placard & if tires have been upsized inflate to sidewall max inflation, they have been designed to handle the pressure increases due to temperature.

[sourdough]

Your tires should be run at the psi on the placard on the side of the trailer - 80psi unless you want to have an unhappy experience with your tires at 65mph (or whatever speed you drive).

[CWtheMan]

There are three places to find the correct inflation pressures for OEM sized tires for RV trailers.

1: The vehicle owner's manual.
2: The vehicle federal certification label.
3: The tire and load information label.

[notanlines]

Tony, you have now gotten the correct answer from members who do not wear their caps backward on their head, nor cocked sideways. Their answers are based on fact, not "Well, it seems to me...."
And I believe upgrading your tires from your Goodride brand is a good idea.

[CedarCreekWoody]

The minimum PSI is that on the placard on your camper. The maximum PSI is stamped on the tire. Run at either of those numbers or pick a number between the min/max. Your choice.

Edit: over time observe tire tread wear and adjust accordingly.

[JRTJH]

^^^ What Woody said makes sense, but remember this "simple fact":

If you're buying upgraded tires to increase the load reserve capacity, then reduce the pressure for whatever reason, reducing the load reserve capacity, what have you gained ???

In other words, if your trailer has LRD tires designed for 65PSI and you buy LRE tires and run them at 65PSI, then you do not have an increase in load reserve, you have tires capacity equal to the LRD tires. The only increase you've attained is an increase in purchase price..... Think about it .....

[dutchmensport]

Well, when I changed my factory installed tires because of a blow out, I ended up getting Hercules tires (14 ply) from a Semi Truck repair shop. (we were traveling and this was the only place anywhere to get anything for the trailer).

Well, the placard on the trailer says 95 psi. The tires say 105 psi. So, I compromised and keep the trailer tires at 100. This seems to work for me.

And yes, I 100% agree that no one should ever drive faster than the speed limit rating of the tires on your trailer, unless you simply have a death wish. If the trailer tires are rated at 65 mph and the speed limit is 80... you still should never run faster than 65. Don't let the grim reaper take one of your family memebers. (scary I know, but true!)

[jadatis]

Goal of pressure determination is to give the tire a deflection, so heatproduduction a cycle, that wont overheat any part of tire material when driving the speed constantly, the pressure is determined for.

Tiremakers give lists for that, but for ST its for 65mph.
And sometimes higher speed is used.

The deflection is made by the pressure/ weight combination.

On your tire is given that when you have maxload of 2830lbs on tire AT 80psi, that then it gives a deflection, so heatproduction a cycle, that wont give overheating of any part of tire , when driving constant speed of 65mph. Mayby a little reserve is build in , but dont count on it.

The pressure/ loadcapacity- lists are made with a formula ( that I once got hold of and went running with) with goal to keep the deflection , so heatproduction, the same.

Then a 80psi E-load tire, needs a bit higger pressure to carry the same load, then a 65psi D-load tire , because its stiffer to keep higher pressure in, wich gives a larger overgoin curve from unloaded radius to flat on the ground, so shorter and lesser surface on the ground.

So if your OEM D- loads would need 65psi to laws of nature, the E-load would need higher, estimated 70 psi for that same load.

ST lists are made with a formula introduced for diagonal tires in 1928. For radial tires in the 1970ties this formula was changed to one that gives higher pressure for the load, or lower loadcaoacity for the pressure.

When I calculate it for TT and 5thwh I use an even saver formula, and first add 11% to the given axleload, to make the average % used of the loadcapacity for the pressure 90%

This to build in a reserve for things like:
Pressureloss in time
Unequall load R/L
Misyudged loads
Inacuracies in pressure and weight measurement.
Etc, etc.

So in short, basics are simple, but in practice many bears along the road.

I also figured out the speed/ maxload relation.
So for the larger ST tires I substract 6 loadindex steps first, to give the tire a deflection it would need for 99mph ( speedcode Q and higher) .
This together with the 11% adding to given axleload, gives highest reserve, without screws or rivets trembling loose
So I dont search for the lowest save pressure but the highest " comfortable" pressure.

So to make this already to long story short.
Your 65psi is probably to low, but 80psi not needed
Have to calculate it for you, but think 70 to 75 psi it will come to. Cold pressure, so if driving it rises to 90 psi no problem , they dont put for no reason cold on it, they know it may rise above the 80 psi when driving.

[jadatis]

Filled in my calculator with your 7700lbs total weight ( assuming its right, your responcibility)
And 2830 lbs maxload At 80 psi. Reduced by 6li steps to LI 111/ maxload 2403 lbs
Gave only 63psi, and this is because in this case the tires have a comfortable reserve.
Using the D- load 2540 lbs AT 65psi reduced 6 LI steps to 2094lbs gave 60 psi.
4x 2094= 8376lbs the tires can carry at 65psi, and assumed 10% on towplate
So average of 7700-770= 6930 on the 4 wheels .

[KJLarson]

I read this stuff about the correct psi and wonder where people are getting all the misinformation. First, the psi printed on the sidewall is the max pressure the tire is designed to hold without the potential of failure. It is not the psi that the tire should be inflated to for the TT. The correct inflation pressure is solely based upon the weight the tire is carrying which is determined by looking at the inflation table published by the mfg. In this case take the totally loaded trailer weight as found by having the TT weighed on a commercial scale and divide by the number of tires to arrive at the weight each tire is supporting. Than go to the mfg's inflation table to determine the correct psi that will keep the entire width of the tread on the pavement. If you inflate the tire to the psi on the sidewall rather than the inflation table psi the tire is over inflated and only a small portion of the tread will be on the pavement which can be dangerous. The mfg knows their tires better than the posters here so follow the mfg's recommendations; this will increase the life of the tire and will provide the safest use of their tires.

[flybouy]

Originally Posted by KJLarson

I read this stuff about the correct psi and wonder where people are getting all the misinformation. First, the psi printed on the sidewall is the max pressure the tire is designed to hold without the potential of failure. It is not the psi that the tire should be inflated to for the TT. The correct inflation pressure is solely based upon the weight the tire is carrying which is determined by looking at the inflation table published by the mfg. In this case take the totally loaded trailer weight as found by having the TT weighed on a commercial scale and divide by the number of tires to arrive at the weight each tire is supporting. Than go to the mfg's inflation table to determine the correct psi that will keep the entire width of the tread on the pavement. If you inflate the tire to the psi on the sidewall rather than the inflation table psi the tire is over inflated and only a small portion of the tread will be on the pavement which can be dangerous. The mfg knows their tires better than the posters here so follow the mfg's recommendations; this will increase the life of the tire and will provide the safest use of their tires.

Let's clarify and not misinform by painting with a broad brush. Carlisle Radial Trail HD fitment page https://www.carlislebrandtires.com/o...dial-trail-hd/ says the listed psi is the recommended pressure. For my size that's 80 psi, the same as the "max inflation" molded into the sidewall.

[jasin1]

I’m thinking I will just hire a tire engineer/ consultant..put him on the payroll and have him travel with me to adjust the air pressure up and down based on how much we buy at antique shops in our travels and how much water is in the fresh water tank.

Do I need to air the tires up differently based on each individual tire load?

tires are really complicated

Yeah I’m not going thru all of that lol

[sourdough]

Originally Posted by KJLarson

I read this stuff about the correct psi and wonder where people are getting all the misinformation. First, the psi printed on the sidewall is the max pressure the tire is designed to hold without the potential of failure. It is not the psi that the tire should be inflated to for the TT. The correct inflation pressure is solely based upon the weight the tire is carrying which is determined by looking at the inflation table published by the mfg. In this case take the totally loaded trailer weight as found by having the TT weighed on a commercial scale and divide by the number of tires to arrive at the weight each tire is supporting. Than go to the mfg's inflation table to determine the correct psi that will keep the entire width of the tread on the pavement. If you inflate the tire to the psi on the sidewall rather than the inflation table psi the tire is over inflated and only a small portion of the tread will be on the pavement which can be dangerous. The mfg knows their tires better than the posters here so follow the mfg's recommendations; this will increase the life of the tire and will provide the safest use of their tires.

I think you are confusing auto tires with ST trailer tires. My last 2 trailers (the 2 that I recall) had the max psi of the OEM tires on the RV placard on the front left of the trailer. The manufacturer called for inflating the tires to the max pressure on the tire - not a table.

Here is an excerpt from etrailer explaining why ST tires run at the listed max pressure;

"Expert Reply:
The trailer tire manufacturers we work with all have recommended the information you have seen given in our online answers. The max PSI from most manufacturers the listed capacity at the highest load capacity rating of the ST tire.

There are charts as you stated to give you a variable psi level from certain manufacturers, like Goodyear and Maxxis for instance, that have their primary business in automotive tires. They have testing of these levels built into their system where most ST specific trailer tire manufacturers do not. The reason why they do not do as extensive testing on their tires is because of the function. Trailer tires have a stronger sidewall because they are not used for turning in the same way as the front axle of a vehicle tire is. Also, it is very rare for a person with a trailer to weigh their load each time and adjust the pressure accordingly and tire failure is most of the time attributed to not having enough or having too much air in the tires for proper use. The max psi is the safest place to keep the tires inflated whether traveling empty or fully loaded to give you best traction with an ST tire and that is the majority of the reason why we recommend it. We even have one company that uses Nitrogen to better keep the tires at the max psi."

[Tireman9]

Again, as an actual tire design engineer w/40+ years experience I will try and clarify the sidewall psi information.
As i said Mar 4 on my RV Tire Safety blog to the question Your tire says Max xx psi at Max Load of yyy Pounds" Will your tire blow up if you go above xx psi?


"The simple answer is No. Your undamaged tires are not going to Blowout or Explode or Blowup if you see a pressure greater than xx psi on your TPMS or on your hand gauge.
There is a lot of confusion out there because people do not understand the reason for the confusing wording that is mandated by DOT.
There are Federal regulations on the words and information that must be molded on the tire sidewall. This wording has been around for years with some unchanged since the 1960's.
A recent poll of RV owners responding to a question on tire inflation number on the tire sidewall indicates that 18% think the inflation number molded on a tire sidewall number is the absolute highest a tire should ever have in it. Another 18% think that inflation is "the best" inflation for the tire 2% think it's the lowest pressure the tire should ever have. I am very disappointed with this level of confusion.
Here is the reality:
Each type and size tire and Load Range has a stated Maximum load it should ever be subjected to. The number is molded on the tire sidewall in both pounds and Kg. The tire industry has published tables that provide the MINIMUM inflation a given tire needs to support a stated load. The tables clearly state that the inflation number is the inflation measured before the tire is driven or warmed by direct sunlight. This is called "Cold Inflation". Not "Refrigerated" inflation and not some laboratory 68F or 70F "standard, but the inflation that would be the same as the surrounding ambient air. Some people know this as the "Temperature in the shade".
The confusion comes about because until recently vehicle owners never knew the operating temperature and pressure of their tires. However with the introduction of aftermarket TPMS as used by many RV owners, they now have those numbers presented to them.
What is missing are two things. One being training by the selling dealer as to what inflation is needed to support the stated load and second an explanation of what the words on the tire actually mean.
I am not sure if the RV salesman has ever received the training other than to tell the customer the information is in the Owner's Manual.

Hopefully when an RV owner reads "Max Load" they understand that they should never load the tire more than that.
The confusion comes with the inclusion of the word Max as it relates to tire pressure.
IMO the wording would be much better and more logical if the tire said "Max Load yyyy pounds at xx Psi cold".
I would leave it up to the people at DOT to try and explain why they were not consistent across all types of tires with the wording on load and inflation limits, but I have no idea who to ask. as I expect them to pass the question off and say "Ask the tire manufacturer" but the manufacturer is only following the regulations established by DOT.

I have a large number of posts in my blog that mention inflation. If you have questions I can suggest you review my posts as the questions are asked a few different ways and I provide the answer with what I believe is a consistent interpretation of the intent of the requirements."


The OP had other questions. Most have been correctly answered by other posters. I have posted answers for all the questions along with an explanation of why RV trailers should run their tires at what may seem to be "High" inflation. If you Google "Interply Shear tires" you can learn the reason.

[Tireman9]

Originally Posted by jasin1

I’m thinking I will just hire a tire engineer/ consultant..put him on the payroll and have him travel with me to adjust the air pressure up and down based on how much we buy at antique shops in our travels and how much water is in the fresh water tank.

Do I need to air the tires up differently based on each individual tire load?

tires are really complicated

Yeah I’m not going thru all of that lol

As a tire engineer I can tell you that you should not be adjusting your tires up & down based on how many cans of beans you buy. We advise to AT A MINIMUM learn the heaviest you would load your tires. We then advise you to NEVER run a pressure lower than the PSI found in the Load/Infl tables. You will hear the few (2 or 3) actual tire engineers on various RV forums advise you run at least 15% more inflation to maybe 25% more inflation than found in the tables in an effort to at least partially counteract the Interply Shear forces that multi-axle trailers place on the tires in RV application.


Weight it. Learn the Minimum infl. Add 25%. Monitor inflation ALL THE TIME (TPMS). Inspect your tires at least once a year with a "Free-Spin" inspection. Go camping.

[Roper46]

When I got my 5er last August, all the valve stems had green colored caps on them. From what I have read this indicates the tires have Nitrogen in them.

Is this correct? And if it is correct what if any special "handling" does this mean?