tire air pressure

Before getting into this let me remind the readers of this thread that I’m not directing a response to any single participant unless I have used the quote tab to do so. This is directed at the thread subject in general.

Sometimes participants in RV trailer tire threads are more familiar with the maintenance procedures for automotive tires. Those tires (P - LT - RV - Truck) are designed to provide reserve load capacity via tire pressure manipulations. The builders of automotive industry vehicles are always going to provide load capacity reserves with the Original Equipment (OE) tires. That is not a requirement for tire fitments to RV trailer axles. Another confusing factor is the design of the ST tire. They are best equipped to operate at maximum allowed tire pressures. Trailer manufacturers take advantage of the ST tire industries recommendations to use maximum sidewall pressures. There is only one - known to me - ST manufacturer that will allow tire manipulations above the maximum sidewall pressure and that is Goodyear. So if you’re not using their brand of ST tires than don’t consider going higher with your air pressures than what’s on the tires sidewall for any reason.

There is something common to all DOT certified highway tires, Their recommended (correct) tire pressures are set by the vehicle manufacturer. NHTSA always presents a statement about that in large red letters anytime they are stressing that fact. That’s not to say there aren’t exceptions because there are always exceptions. It’s just stressing the point that normal everyday tire operating pressures are found on the vehicle’s certification label/tire placard.

The problem for RV trailer owners is the fact that their trailer’s tires recommended tire pressures are 99.9% of the time maxed out. So, where do you go from there? There is no higher to go to and surely you don’t want to go lower and enter the realm of under inflated tires that are going to start throwing the treads. All you can do is insure they are aired to the 100% mark all the time and then replace them with something that will provide a larger measure of load capacity reserves.

FastEagle

3Fivers51:
What can I say except to say, I'm sorry. You already said that this was hashed out some time ago and it seems that the thread has gone down the wrong road for you. So...what have you learned from all of this? Maybe you should try reducing your air pressure a bit. How much? I don't know since I don't know the axle weights for your TV and RV, nor do I know what kind of tires are on each. I would tell you that finding the "sweet" spot for all of the tires on your rig is a bit of science and art, trial and error.

Good luck.

As per usual my post has drawn negative responses. My message IS NOT what you all, as individuals, can do with your trailer’s tire pressures. My message is WHAT the industry as a whole accepts as being correct.

Those that advocate using only enough tire pressure to support the weight the units axles are supporting are sometimes the same people that get angry with trailer manufacturers that they feel are not providing enough reserve load capacity with their Original Equipment (OE) tires. I personally believe that any tires used on RV trailers should have a minimum - by air pressure - of 12-15% load capacity reserve above GAWR to offset the dynamics of the tall vehicle’s bobbing and swaying actions.

FastEagle

Cummins12V98 wrote:



"MeAgain has a perfect example of why you should know your weights and apply the knowledge that is available to you.

Use your brain people!

But we must consider where the brain must go to find the proper information to use.

Tire industry standards are very clear on that subject. And they are the same for motorized vehicles. Plus sized tires are to be aired to a minimum value equal to what the vehicle manufacturer has set the OE tires to. In other words, the replacement tires MUST - their word -provide equal or greater load capacity as the OE tires. When your engineering skills come into play and you start saying "ya but" and that causes you to jump away from industry standards for some particular reason you're on your own with that decision. I'm really not comfortable making recommendations out side of the ropes - so to speak. What works for me stays with me unless it's an approved and tested procedure.

FastEagle

FE

Your quote below.

"Tire inflation charts are a tool for experienced tire technicians and others that know how and when to apply them to the trade"


I agree!

Like I said this is a CYA world. I have never been a "sheeple" that just does what he is told.

MeAgain has a perfect example of why you should know your weights and apply the knowledge that is available to you.

Use your brain people!

As a automotive mechanic for 39 years, I can tell you that you cannot always trust the manufacturer. I will give you a very good example: The nineties Ford Explorer. Ford recommended 26 psi in the tires for no other reason than to give a softer ride. Firestone recommended 30 psi. This from John Lampe, Firestone VP, "The 26-pound level left little safety margin," Lampe said. Heat that can cause a failure builds up faster in a flatter tire carrying a heavy load in hot weather. (Ford said 26 psi is safe but recently accepted Firestone's recommendation and increased the suggested tire pressure to 30 psi.) When designing the Explorer the engineers recommended that the Explorer be a couple of inches wider for stability. The powers that be ignored that suggestion and also used tires that did not have the extra nylon cap.
Another example: For the last 16 years I have worked for a government fleet garage. A few years ago, a tire rep recommended 51 psi in the tires for police cars. Now the sidewall does list 51 psi as max pressure, but in real life it was bad advice. The complaints came in almost immediately from the officers, no traction. The pressure was lowered to 40psi and the problems went away. The point is, things are not always black and white.

Me Again wrote:
So FE as I have posted before. Two trailers of similar size and weight. Mine a 29 ft Cardinal buddies was a 29 ft Montana. Both with 5200 axles and OEM LT235/85R16E's. Mine stated 65 pounds inflation and his 80 pounds. 65 pounds happens to match industry standard inflation charts for the weight on the axles.

So I have a lot less faith in what trailer manufacturers put on placards than you do. My placard would indicate his tires were over inflated and his placard would indicate mine were under inflated.

Somewhere people have to learn to think for themselves or go to a good commercial tire shop and talk to techs the deal with customers that make a living day in and day out with their rigs.

In repeated calls to Michelin's CS I was advised to follow the inflation charts if I knew my weights. They stated that over inflation reduced contact patch/braking and increased chances of impact damage.

After many years of service from my RIBs I settled in at 71 lbs inflation based on wear patterns. Tires were in service for 6.5 years and 40K+ miles. I run the new(2 years old now) R250's at the same 71 pounds.

Of course I choose to spend the money for the best tires available for a trailer my size and do not have to worry about ripping the cap off the carcass as jimnlin noted above.

I have long thought the ST tread pattern, tight cornering and light construction was part of their downfall.

Chris

Exactly right.

The pressure on the sidewall is the pressure needed to carry the maximum load the tire is designed for. If you are running lighter than near the max, then you should go to the tire inflation charts. I tend to run a little more pressure than the charts call for. But, if I am loaded only to 60% of the wt capacity of the tire, running at max pressure will shorten tire life, and cause a very rough ride.

That being said, if you are running the tires that came on the trailer, you probably need to run the max on the sidewall, as they usually only put on the minimum tire on that is rated for the load.

I like to go to a better tire, with more capacity, and then run the pressure at less than max on the sidewall. Better tire equals less tire problems.

So FE as I have posted before. Two trailers of similar size and weight. Mine a 29 ft Cardinal buddies was a 29 ft Montana. Both with 5200 axles and OEM LT235/85R16E's. Mine stated 65 pounds inflation and his 80 pounds. 65 pounds happens to match industry standard inflation charts for the weight on the axles.

So I have a lot less faith in what trailer manufacturers put on placards than you do. My placard would indicate his tires were over inflated and his placard would indicate mine were under inflated.

Somewhere people have to learn to think for themselves or go to a good commercial tire shop and talk to techs the deal with customers that make a living day in and day out with their rigs.

In repeated calls to Michelin's CS I was advised to follow the inflation charts if I knew my weights. They stated that over inflation reduced contact patch/braking and increased chances of impact damage.

After many years of service from my RIBs I settled in at 71 lbs inflation based on wear patterns. Tires were in service for 6.5 years and 40K+ miles. I run the new(2 years old now) R250's at the same 71 pounds.

Of course I choose to spend the money for the best tires available for a trailer my size and do not have to worry about ripping the cap off the carcass as jimnlin noted above.

I have long thought the ST tread pattern, tight cornering and light construction was part of their downfall.

Chris

Goodyear Tire and Rubber .... weighing RVs website.
Special Considerations

Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire. Trailer tires experience significant lateral (side-to-side) loads due to vehicle sway from uneven roads or passing vehicles. Using the inflation pressure engraved on the sidewall will provide optimum load carrying capacity and minimize heat build-up."

and from;

rvsafety.com

Tire Load and Inflation Ratings

Note: Towable – Travel Trailer/ 5th Wheel owners Due to the severe use conditions experienced by tires when axles are very close together – tire industry experts recommend maximum (sidewall) inflation pressure for towable tires unless this causes a sever over-inflation situation (20psi+), often referred to as the ‘basketball effect’. If this is your situation allow a 10 – 15psi safety margin above the minimum required inflation pressure."


And this from Tireman9 one of our resident tire engineers who says this about RV mfg setting tire pressures;

"The manufacturers do not take into consideration the side to side unbalance, as to do so would require them to provide larger (more expensive) tires. The other thing RV industry does not take into consideration is the forces to the tire structure due to running close axle spacing. Engineering analysis shows that when turning corners the forces trying to tear the tire apart can be over 20% higher in multi-axle applications than with tires at the corners of the vehicle.
The only options for the trailer owner are to up-size the tires (if there is room) or up-rate and increase inflation (if a higher Load Range tire and stronger wheels are available). Lacking the above being sure to run the tire at the inflation shown on the sidewall (i.e. max) will slightly decrease but not eliminate the overload forces." end of quote..


Tire pressure numbers on a placard are a recommendation only and is not the last word in the best pressure for the tires on any vehicle and especially a trailer.
Many trailers out here don't have a tire placard. We learned the hard way what pressures worked best and which didn't.

Cummins12V98 wrote:

FastEagle wrote:

spindrift wrote:

3Fivers51 wrote:
Ok spindrift, what do you suggest or what is your take on this? I also got a lot of information from a cooper tire rep.
Thanks for your impute it is always a good tool for guidance!
Bill

I believe you should have a load inflation table from your tire manufacturer, properly weigh your rig and then inflate your tires to the appropriate pressure based upon the manufacturer's recommendation.

This is a simple truth. Tire manufacturers do not set recommended (correct) tire pressures. Vehicle manufacturers do. So the correct recommend tire pressure for your tires is found on the vehicle's federal certification label for all original equipment tires and any replacements that are the same size and design as the OE tires.

FE

That is a CYA number and you know it!

Weigh your RV fully loaded, all 4 tires if you want. Use the tire weight/inflation guide and add 5psi. Per GY tech support if you have changed tire sizes or load range. They could not say to change what is on the RV for pressure "CYA" again. But let's use some common sense here!

They usually put tires on RV's that in reality add up to Max tire weight rating.

If you are one to add very little weight to your RV or have changed tire sizes then please weigh your RV and use the charts.

Same goes with your TV.

At this point of time in this particular forum all I can do is point out industry standards. My posts have been disparaged so often that anything I say must be “BS”.

Here is a reference from a well known tire manufacturer. Read it carefully. They will not use any tire pressures lower than the vehicle manufacturers recommendations. This is just a single reference. I can post others from other tire manufacturers just as popular as this one and from what many consider the top of the line manufacturers.

Tire inflation charts are a tool for experienced tire technicians and others that know how and when to apply them to the trade.

Weigh Form Ref

FastEagle