Tire pressures

[Tireman9]

OK lets see if I can answer the questions on this thread.

First off you might care to know that I an a retired Tire Design and Forensic engineer with 50+ years experience designing, testing, working with and inspecting Truck, Passenger, Indy, LT and ST tires.

Next you need to remember we are talking about the "cold" inflation which means when the tire is at Ambient air temperature and has not been driven or in direct sunlight for the previous two hours.

To answer the question of "MAX PSI" on a tire sidewall mentioned in a number of posts:
Every vehicle has a Certification Label. That states the Tire Size, and the recommended inflation if it is a passenger car. If it is an RV it will give the GAWR, Tire Size, Tire Load Range and the inflation required to support the GAWR. Passenger car inflation are arrived at after years of testing and evaluation of different tire designs from different manufacturers at different inflation that balance the requirements on a long list (100's of items) from the car company. These requirements include Force & Moment test results and fuel economy plus dozens of detailed ratings within each category for Ride, Handling and Noise. Car inflation are a "Recommendation" from the engineers at the car company aimed at giving the you the performance they designed into the car.
RV companies do not evaluate tires. They generally look for the lowest cost tire that can provide the load capacity required by law. This usually means for towables that the tires would need to be inflated to the level required to deliver the max load capacity.
The inflation number on a tire sidewall is the PSI needed to deliver the Max Load rating stated on the tire. Normally tire load capacity is increased with an increase in inflation and that would normally mean you would increase the inflation, BUT since the tire was selected for it's max load capacity the tire states on the tire sidewall, the inflation that will deliver the highest load capacity for that tire is already on the tire.
Yes the wording is confusing but the wording was selected by the lawyers not tire engineers.
Motorhomes are built on chassis built and designed by vehicle manufacturers so the tires on Motorhomes will many times have inflation lower than the tire max.
Many towables are built with minimal capacity for additional "stuff" but many load their RV with no thought to the load capacity. This is why the data shows that over half the RV on the road have one or more tire or axle in overload. This is why there are so many tire failures.

Too often people do not pay attention to what type of vehicle is being discussed A Passenger car (or 1/2 tom Pickup) or a Motorhome or a Trailer (5th wheel). These three completely different types of vehicles require three different guidelines and inflation information.




I have to run but will be back to address the other issues raised.

[ajef7885]

Originally Posted by craigav

The door pillar placards are not always the optimal tire pressures imo and in particular for pickup trucks. If you notice, the placard tire pressure recommendations are always made as if you are using the truck at the heaviest weight (load) that the truck is rated for. So if you are a person who uses their pickup truck without any load in the bed for extended periods of time, then a lower tire pressure than the door jamb placard recommends will definitely provide for a better ride, better traction, as well as better road control as Kevin mentioned above. ~CA

Of course if\when your truck is fully loaded, then the air pressure needs to be adjusted for the full load which then will be what the tire pressure placard states.

I looked up the load rating on the Goodyear Wrangler LT Kevlar tires on my F150. They would need to be ran at 50 PSI for the max axle loading on the truck. 39 PSI on the door placard falls on the load chart about where the truck has nothing in the bed or loaded on the rear axle (i.e. trailer). So by that I run 39 normal, 50 when pulling the camper.

[Kevin Cooper]

Tireman9, Looking forward to your insight! Always better to learn from an expert than a novice.

[Jaykol]

My trailer has Goodyear Endurance tires that have a load capacity way above any conceivable weight I could load it too. I over estimated my total load and applied my tire pressure accordingly to the Goodyear chart and am totally happy with the result. My two cents is going to max inflation by default causes a bouncy trailer and makes me wonder about how many people that talk about microwave glass coming out or tables flipping over are really about over inflation.

Kevin and all - this forum is mostly very positive and understanding but the two things I have noted as polarizing are tire pressure and the speed in which one must pull their RV. In other forums often we see similar things, a few motorcycle forums fought endlessly about the right oil and change frequency. And for those who complain about "another tire pressure thread", no one is asking you to read it! I read them and shrug and laugh or consider a new point of view.

[Ceimo]

My 2022 Jayco North Point 310 RLTS came with Good year Endurance 16” ST tires with E rated tires. Double checked with Goodyear and the 80 PSI cold Max is correct.
Using the Tire Pressure monitors you’ll see 10 min. Into a drive the psi is 90-93.
The alarm is best set at 100 and low at 70.
Also seeing side in the sun is a few PSI higher than shaded side.
With this technology it makes staying in the safe margins in real time a no brainer on towing safe. If you get an alarm it will save you from a potential blow out.
I have put 20k miles on already and tire wear is even.

[ElRey]

The white sticker on my 212QB says to inflate my Endurance tires to 65lbs. The F150 door sticker says inflate my P tires to 35lbs.. Not rocket surgery.

[Kevin Cooper]

A 310rlts gross loaded weight is 15000 lbs. the dry hitch weight is 2510. 15000-2510=12490lbs on both axels. 12490/4(tires)=3122 lbs per tire. Your tires are 255/85r16E.
At 80lbs, it is rated at 4080x4=16320lbs. At 50lbs, the tires are rated at 3200. Give 10% for safety, 55lbs would be 3360x4=13440. All this assumes 100% cargo capacity is used.

[Cincinnati Kid]

My trailer says to inflate to 80#- the maximum sidewall pressure, so I do. End of story for the trailer........
My truck says 60 front, and 65 rear. NOT end of story. The tire companies give you charts for tire pressure under various loads, then tell you to do what the manufacturer says.
The owners manual is very vague regarding tire pressure under load conditions. I wish they would just come out and tell you what pressure at what load. But they don't, and that's why these threads go on for as long as they do.

[BicycleMark]

Hey Kevin,

Perhaps I missed it, but I've not seen any comments regarding the suspension. Tires are an integral part. Trailers have suspensions designed to incorporate tires inflated at the pressure stated on the sticker. Inflating your tires to a higher pressure will negatively affect the suspension, adding higher stress forces to suspension components including the frame. Higher tire pressures may also negatively affect handling.

Just my 2 cents,
Mark

[Tireman9]

Originally Posted by Cincinnati Kid

My trailer says to inflate to 80#- the maximum sidewall pressure, so I do. End of story for the trailer........
My truck says 60 front, and 65 rear. NOT end of story. The tire companies give you charts for tire pressure under various loads, then tell you to do what the manufacturer says.
The owners manual is very vague regarding tire pressure under load conditions. I wish they would just come out and tell you what pressure at what load. But they don't, and that's why these threads go on for as long as they do.

In my experience, the Owner's manuals range from good to a waste of paper. Some are just a collection of documents from other component manufacturers.
For tires just get the pages that cover your RV and your tow vehicle and that will answer all your questions on what inflation at what load.
https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf


FYI You will find that almost all tire companies follow almost identical numbers in the charts.

[Tireman9]

I am wondering how many on this thread have read THIS post.




Do you want more info? or am I wasting my time?

[El Chupacabra]

Originally Posted by Tireman9

I am wondering how many on this thread have read THIS post.




Do you want more info? or am I wasting my time?

I'm curious what you think of using sufficient load range truck tires (eg, an E-rated tire) on a trailer, instead of ST-rated trailer specific tires. Some trailers (usually smaller ones, it seems) actually come with LT tires instead of ST.

Apologies for the thread drift away from PSI...

[Grumpy]

Originally Posted by Tireman9

I am wondering how many on this thread have read THIS post.




Do you want more info? or am I wasting my time?

Yes to both. Many will enjoy reading and following the correct information and yet others will continue to ignore it.

[Kevin Cooper]

Originally Posted by El Chupacabra

I'm curious what you think of using sufficient load range truck tires (eg, an E-rated tire) on a trailer, instead of ST-rated trailer specific tires. Some trailers (usually smaller ones, it seems) actually come with LT tires instead of ST.

Apologies for the thread drift away from PSI...

Goodyear makes a tire that is LT rated and also rated for trailers. So, you can’t just say, use LT tires and good to go. There may be others, but I have not looked for them.

[Kevin Cooper]

Originally Posted by Tireman9

I am wondering how many on this thread have read THIS post.




Do you want more info? or am I wasting my time?

Could you please also include some information about speed ratings? I have gotten a couple statements of meaning. Maximum speed, and best performance up to that speed. Respectfully, Kevin

[Ceimo]

I Agree with Elrey, Good lord it’s not rocket science🙄
My Chevy Silverado 2500 High country states 70 psi rear and 60 psi front.
When going down the road once heated up they read 80 back 70 front.
My rig says 80 cold on E rated Goodyear Endurance. When running the show 90-93 when hot.
Understand the simple science.
Ask any trucker when fueling up😉

[Bocafeet]

i feel the same way but i have found no help in determining how much pressure is correct for “hot” tires during a gas stop. usually i match the highest pressure tire or go 5lbs over “cold” #. who the hell knows. over the life time of the tread i also go over or under to force more wear to center or outer tread to even out wear within 5-10% am i wrong?

[Kevin Cooper]

Originally Posted by Bocafeet

i feel the same way but i have found no help in determining how much pressure is correct for “hot” tires during a gas stop. usually i match the highest pressure tire or go 5lbs over “cold” #. who the hell knows. over the life time of the tread i also go over or under to force more wear to center or outer tread to even out wear within 5-10% am i wrong?

So, when you are running max pressure, you are wearing in the center, so you run high for a while, then lower pressure to even your treadwear. Just a thought. Find the sticker from the manufacturer, use that pressure, and achieve some advantages. Less tire wear. Better traction on corners. Better traction when braking. Smoother ride not bouncing so much. Less damage to tires when hitting a pothole. Less strain on your springs.

[Bocafeet]

Again ,, find me a sticker that lists hot pressure. you are just arguing with your self

[Bocafeet]

even tire wear is the key. everyone has to have his “thing”