Tire Pressure Recommendation for 5th Wheel

[Craig and Linda]

Hi,
I have a 13,000+ lb dual axel 5th wheel with 235/80R16 Tires.  I have always kept the cold psi at 80lbs each, because that is what is printed on the tires.
Have always wondered if I was correct in doing so.
Anyone know what is recommended?
Craig

 

[Memtb]

  I would, and then monitor wear pattern! However, there are charts available via the internet that will give load capacity @ various tire pressures! Weigh your weights at each axle....and air tires accordingly.

 

[Gary RV_Wizard]

The psi on the sidewall is the pressure needed for carrying the tires max rated load.  Given that most RV trailers are built with only minimally adequate axles, you very likely do need the max, or close to it.

A typical 13,000 lb 5W carries 80% of its weight on the axles, so estimate 80% x 13000 = 10,400 on two axles. 5200 lbs each. a typical 235/80R16 tires can carry 3042 lbs at 80 psi or 6084 per axle. That's about right, allowing for some safety margin, temperature changes, unbalanced loading, etc.

However, you said "13,000+" and that is a bit worrisome.  If it's actually closer to 14,000, you are very near the tire limits and might want to consider larger tires (greater load capacity).

 

[jadatis]

Knowing the real weight in use on axles, or better axle-ends, is the most important. Determining that is the most tricky part in it all.

Then when this is sorted out, you come to the tires.
Mostly they ar ST tires wich are calculated in maxload for 65mph, wich allows more deflection before overheating.
But this brings it to the limits of savety, a bit more speed or load on tire, and/or a bit lower pressure, and the tire overheats,
This must never happen even only once in the tires life.
So its better to give ST tires a deflection, as if it was a LT tire , wich is calculated in maxload for 99mph, and even add 10% to the accurately determined loads on axles, for unbalance R/L , and pressure dropp in time.
Then still no bumping, and gripp still acceptable.
Thats the reason why ST are adviced on maximum given on tire, and for laws of nature, often an even higher pressure would be needed, wich tiremakers dont allow anymore.
So switching to LT tires with even same maxload would be better, but need higher maxpress for that same maxload and sise tire.

 

[FastEagle]

This is a subject that is always disputed. Because I like to stick to the ways things are supposed to be done I?m going to post it that way.

For original equipment tires there is a single rule. The vehicle manufacturer is authorized by regulations as the only ones eligible to set recommended cold inflation pressures for your original equipment trailer tires. NHTSA prints numerous tire safety documents. All of them will tell us the correct inflation pressures for our tires are displayed on the trailer?s federal certification label, on the tire placard and in the vehicle owner?s manual.

The USTMA has a published document that includes their industry standards for RV tires. Tire industry standards will not over rule the NHTSA for Original Equipment tire fitments by the vehicle manufacturers. The following quote is from the tire industry document. ?Never use inflation pressure lower than specified by the vehicle tire placard, certification label or owner?s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.?

Probably 95% of all OEM tires have vehicle manufacturer recommended cold inflation pressures that are equal to the tire manufacturers maximum load pressures depicted on the tire sidewall. Therefore there is no (approved) possible adjustment. Just keep them aired to the max and go. Will that max air policy change with the RVIA recommendations? I doubt it. The 10% reserve load capacity RVIA recommends is only attainable with air pressure so max will still be preferred.

The rules do not change with replacement tires. They just become more complicated. The tire industry standards stick with the vehicle manufacturer?s recommended load capacity the OE tires provided. Their basic statement is like this; Replacement tires must provide a load capacity equal to or greater than the OE tires provided (via inflation).

Those replacement options put a new twist on recommended cold tire inflation pressures. It becomes the responsibility of the tire installer to insure the minimum standard is met. ?Plus Sized? tires may not need to use all of the load capacity reserves they are capable of. The minimum will be to equal the OEM tires capabilities. After that everything is optional. Once the installer determines the inflation pressures needed to satisfy the minimum standard and owner requests, they should make a notation in the owner manual as to the new tire sizes and their recommended cold inflation pressure. NHTSA allows the use of an auxiliary tire placard for plus sized tires. It should be affixed next to the original tire placard.

The rules and regulations for commercial vehicle tires are found in the FMCSA. They are not applicable to vehicles built and fitted for the road using FMVSS (standards).

The FMCSA rule most commonly misused on RV trailer tires is the rule for inflation to the load carried. Not only is it misused, it?s counterproductive to an industry that has no oversight for under inflation like the commercial industry has.

SIMPLICITY: ST225/75R15 is a designated tire size. It may have more than one load range. A load range increase for a designated size does not change the designated size. Therefor, the load inflation chart for that designated size is valid for all load ranges within that designated size. Your vehicle certification label is valid when replacement tires are of the same designated size with a load range increase. 

 

[Memtb]

  If I read the preceeding post (FastEagle) correctly....I beg to disagree! On a specific load range tire, example “E”, altering the pressure below “max cold pressure” lowers load capacity and the accompanying chart represents this! This is just an example, I’m sure that other sizes and load ratings have similar charts.

  “If” you know your tire position loads, you can adjust tire pressure accordingly! Though, I would adjust higher, with at least a 10% factor!

            https://tirepressure.com/lt235-85r16-tire-pressure

 

[BIG JOE]

Hi,
I have a 13,000+ lb dual axel 5th wheel with 235/80R16 Tires.  I have always kept the cold psi at 80lbs each, because that is what is printed on the tires.
Have always wondered if I was correct in doing so.
Anyone know what is recommended?
Craig

Another .02 ?

Get your FW trailer Weighed on a CAT scale. Note the [Total] of the Actual Trailer (now KNOWN*) axel weight(s). Divide that total weight by 4. Go On-Line* to the Tire Manufactures PSI load chart for the series/model and size of the tires, for recommended PSI.. per tire. Air up accordingly.

* in your Post you stated 13,000+LB's. you need to know the [ACTUAl] WEIGHT, hooked up and loaded to go.
* you can also Call the tire maker and ask for PSI Tech Support ?

 

[FastEagle]

Another .02 ?

Get your FW trailer Weighed on a CAT scale. Note the [Total] of the Actual Trailer (now KNOWN*) axel weight(s). Divide that total weight by 4. Go On-Line* to the Tire Manufactures PSI load chart for the series/model and size of the tires, for recommended PSI.. per tire. Air up accordingly.

* in your Post you stated 13,000+LB's. you need to know the [ACTUAl] WEIGHT, hooked up and loaded to go.
* you can also Call the tire maker and ask for PSI Tech Support ?

That is a procedure for commercial vehicle tires as explained in my previous post. It's not an applicable procedure for FMVSS certified vehicles. The only time the tire industry recommends such a procedure is for motor home tires and then they add a caveat to NOT USE pressures below vehicle manufacturer cold recommendations.

When FMVSS is the driving force, anything below vehicle manufacturer cold recommendations is considered under inflation.

Please remember I'm using information and quotes from DOT regulations, tire industry standards and retailer standard operating procedures. They don't always jive with the way vehicle owners do things.

All tires have a maximum load capacity. That load capacity number is displayed on the tire sidewall along with an inflation value described by a PSI number. That PSI number is the amount of cold inflation pressure required for your tires to provide their maximum load capacity.

 

[FastEagle]

  If I read the preceeding post (FastEagle) correctly....I beg to disagree! On a specific load range tire, example ?E?, altering the pressure below ?max cold pressure? lowers load capacity and the accompanying chart represents this! This is just an example, I?m sure that other sizes and load ratings have similar charts.

  ?If? you know your tire position loads, you can adjust tire pressure accordingly! Though, I would adjust higher, with at least a 10% factor!

            https://tirepressure.com/lt235-85r16-tire-pressure

I did not post any specifics, just procedures. A LRE tire needs 80 psi to provide it's maximum load capacity. Tire load inflation charts allow vehicle manufacturers and others to use less inflation pressures all the way down to the minimum requirement of the tire. The PSI value found on a tire sidewall is not a recommendation.

 

[Memtb]

I did not post any specifics, just procedures. A LRE tire needs 80 psi to provide it's maximum load capacity. Tire load inflation charts allow vehicle manufacturers and others to use less inflation pressures all the way down to the minimum requirement of the tire. The PSI value found on a tire sidewall is not a recommendation.

OK, as I suspected....I failed to grasp your point!

 

[longhaul]

  Craig and Linda.....
Your doing it right.
On a trailer that heavy 80 psi will give the tires the best  chances for long term reliability and weight carrying performance for a tire in a trailer position with close spaced axle in the center of the vehicle which is completely different than the tires on our tow vehicles with tires at the corners. Apples vs oranges.
  We can weigh our trucks axles that are at the corners and use a different psi in the front vs rear for the load. 

Publication after publication such as these web sites like  rvtiresafety....Goodyear tires.....rvsafety......5thwheelstreet/etc all recommend using the pressure listed on the tires sidewall and give the reasons why which there are several.

I like the one from ;

Goodyear Tire and Rubber .... weighing RVs                 
                          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 a similar  perspective from;

  fifthwheelstreet.com

Step #5..
  Selecting the Correct Tire Pressure for Your Trailer
We at Fifth Wheel St. no longer recommend adjusting trailer tire inflation pressure below the maximum load PSI rating molded on the sidewall (and only if the wheel/rim is appropriately rated) regardless of the measured scaled weight of individual tire or axle positions for all multi-axle trailers.***see their website for the rest of their long recommendation.

 

[Rene T]

After reading all this I'm totally confused but that's me.  I do know that the max tire pressure on my trailer tires is 80 PSI and the tires Are Goodyear Endurance 235/80R16. But I've found that  once the tire heats up, the pressure goes to 85 PSI so when cold, I air them up to 75 PSI. Also, I use a TPMS system and am so happy I do. A couple of times it's saved my butt and damage to the RV.

 

[rbrdriver]

On my rig the tires have stamped on them to air it to 110 pounds. They are "G" rated tires. It is a 16500 GVWR trailer with 2 7000 axles so I reckon it needs that much pressure. Sure seems like a lot of pressure though.  :-\

 

[lynnmor]

After reading all this I'm totally confused but that's me.  I do know that the max tire pressure on my trailer tires is 80 PSI and the tires Are Goodyear Endurance 235/80R16. But I've found that  once the tire heats up, the pressure goes to 85 PSI so when cold, I air them up to 75 PSI.

Some tires use the word "COLD" for the pressure rating, some do not.  I believe that all mean to say cold inflation pressure, but who knows?

 

[FastEagle]

Just some notes.

The thermal dynamic effect tires must suffer has been factored in by the tire manufacturers.

Optional cold inflation pressures are always acceptable. They start at their recommended cold inflation pressures and stop at the maximum value on the individual tire sidewall.

 

[Memtb]

  Simply put.....the ?cold? tire pressure is just that, the pressure on a tire not yet put into service. The tire pressure will increase once in use....this is figured in by the manufacturers. The ?Cold? pressure should be adjusted seasonally....winter to summer! One of the many reasons that it is recommended that tire pressure be checked on a regular basis.

 

[Gary RV_Wizard]

You are over-thinking, Rene.  Do NOT try to anticipate how much pressure increases as the tire warms up.  The recommended psi is always stated as "Cold" pressure, i.e. before the tire is driven on.  The tire engineers who created the inflation tables and sidewall markings have already factored in temperature increases and anything else that might affect operation.

 

[Memtb]

On my rig the tires have stamped on them to air it to 110 pounds. They are "G" rated tires. It is a 16500 GVWR trailer with 2 7000 axles so I reckon it needs that much pressure. Sure seems like a lot of pressure though.  :-\

  rbrdriver, That is the “maximum cold” inflation pressure for the tire. If you want everything “ideal”, though we do not live in a perfect world, the weight on each tire should be determined. Once the tire load is determined, the “cold” inflation pressure can, “not must”, be adjusted accordingly! There are charts available, that give the load capacity for your specific tire load rating at different “cold” inflation pressures. Assuming that the “maximum cold” inflation pressure is “seasonally” adjusted, you will not hurt anything by running the “maximum cold inflation” pressures....even “if” not needed. Running excessive pressure, will increase the “harshness” (rougher ride), and may increase the wear on the tire center (uneven tire wear).  The increased tire wear at the center for most rv’ers is generally “not” an issue, as for most of us, the tires will exceed their safe “life expectancy”, before we wear them out!

 

[FastEagle]

On my rig the tires have stamped on them to air it to 110 pounds. They are "G" rated tires. It is a 16500 GVWR trailer with 2 7000 axles so I reckon it needs that much pressure. Sure seems like a lot of pressure though.  :-\

Because of the Recreational Vehicle Industry Association (RVIA) recommendation; for all participating RV trailer manufacturers to insure all future RV trailers produced by them; are provided with tires that provide,  a minimum of 10% in load capacity reserve load capacity above the vehicle certified maximum axle load on your trailer. For your trailer that would 3850# Per tire. Keystone probably had three tires in their OEM inventory that would meet/exceed that 3850#. They could have used a designated size with a LRF but chose the more durable LRG.

The RV trailer manufacturer cannot do less than the law allows. The RVIA recommendation is just 10% above the minimum allowed by the FMVSS. Your tires inflated to a cold 110 PSI are providing approximately 25% in load capacity reserves.

There is a single word in the FMVSS (standards) that sets the precedent for the vehicle manufacturer's recommended cold inflation pressures to be the minimum standard for that fitment. That word is appropriate. The FMVSS directs the vehicle manufacturer to set recommended cold tire inflation pressures that are appropriate for that particular fitment. Persons in the tire industry that are aware of that wording in the FMVSS will not recommend less for your OE tires. 

 

[BIG JOE]

WOW Guyz & Galz !

My .02 explained:

My CAT Scale trailer axle weight is: 8520lbs. (That's hooked up to the F-350, and loaded for the road)

I had 4 Hercules, All Steel Belted Radial, H-901, G- rated 225-75-R15's mounted 12K miles ago. (to replace the Westlakes*, that came apart) (FWIW)

The Max Cold inflation PSI was 100psi @ 3200lbs per tire for the H-901's, which I thought was excessive.

I called Hercules Tech support.. gave them the above info,, they said: Based on the trailer axle weight, run them at 85psi... I double checked this with my tire shop.. they said 85psi also.

I feel more comfortable.. and the contact patch is 1/2 inch In now, from the outer tread line.. for better/proper
Tire wear ?

* I ran the Westlakes 80psi max Cold, per the tire mold info.. the entire Tread separated from the carcass.. on Two tires.. and rolled to the ditch. The tires.. never went flat. (I say from Over Inflation) (and maybe poor design specs)

No Harm nor Foul here.. maybe we're at a To Each His or Her Own on this subject.. but that's my .02.. explained.