All tires on the same axle should be at the same pressure. When you've got dullys, they often are run at a pressure lower than the steer wheels.

Typically for a RV WITH THE STOCK TIRES YOU WILL NEED run "MAX" sidewall pressure.

If up sizing lets say from "E" to "G" load range then you will need to find your heaviest tire weight and use the weight/inflation chart for your up sized tire and then add 5psi to that number. I went from "E" tires 80psi to "G" tires and I ran 85psi for several thousands of miles and had perfect tread wear and cool temperatures.

Some will tell you to run MAX sidewall pressure no matter what. I completely disagree.

Ratings on the sidewall are under rated.............They can handle a lot more. Better over inflated than under. On my bobcat and car trailer tires I've always run 5-10psi more than the side wall rated psi. Otherwise they always look flat like they were low on air. Never blew one being over.........But blew some being under inflated.

Barbaraok wrote:

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So you are saying that the manufacturers are lying to people?

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 Oh Boy......................Here we go again!

Thanks for all of the posts. Even though there is conflicting information in them, I guess it helps to see what everyone else is doing/has done and what rate of success or failure they have had.

I think that with "formula"you mean a way of handling .

But I got hold of the officially used formula to calculate pressure for a sertain load , the European tyre-makers use, end 2007 and went running with it.

Gathered a lot of information about it and maximum load of tires in time and now even call myself tire-pressure specialist.

What is used by the tire-makers in Pressure/loadcapacity lists is the other way around formula so calculate loadcapacity for a sertain pressure.

But these formula's are related and one can be set over to the other.

Made a spreadsheet for it and will give a picture of a filled in one at the bottom here.

But first I will give copy of text I used in other fora so dont have to write the story again.

Is a general text so can be a little off forum here sometimes.

Tirepressure advice is all about load on tire and speed ( and sometimes about alighnment - camber angle).

 

So if you can give details of car and tires , I can calculate an  advice pressure with some reserve for things like, pressure-loss in time, unequall loading R/L, incidental extra load, misreadings of pressure scales,and misyudging of weight, etc.

 

This is from tires next and can be read from sidewall:

Maximum load or loadindex.

Kind of tire to determine the AT-pressure/pressure needed for the maximum load up to maximum speed of tire, or if lower 160km/99m/h/reference-pressure, wich is not the maximum pressure of tire.

Maximum speed of tire, most given as letter ( Q=160km/99m/h,N=140km/86m/h fi)

If you have offroad or tires looking like that , with large profile blocs that cover a part of sidewall, also mention, they are allowed lesser deflection then a normal road tire, then the tire maker used to determine the maximum load (to my conclusion the case for the Bridgestone tires on Ford Explorer in the Ford/Firestone affaire).

If you cant find all of it give sises of tire and Loadkind, then I will google for it.

 

From car next and mostly can be found on same plate as the original pressure advices:

GAWR and GVWR ( Gross Axle/Vehicle Weight Rating)

But best would be to determine the real weights in your use on seperate tires or estimate it as acurate as possible, by weighing per wheel(pair) or axle.

 

Maximum speed , you dont go over for even a minute in your use, eventually different for different situations, for instance when towing or fully loaded.This apart from trafic regulations, if you drive faster then allowed give that speed. Nature punnisches with tire-failure, police only with a penalty.

 

Here the picture as example.

 

 

Okay, let's not get crazy with this.  Having been trained by the RV Safety & Education Foundation who has very close ties with engineers at all the major tire manufacturers, here's the information we provided in our tire safety seminars.

For trailers, it's easy.  Run the maximum pressure per the tire sidewall and never more than the sidewall maximum pressure.  The tire pressures will increase as you drive and the tires are designed to handle those increased pressures, but don't inflate past the max sidewall pressure.  Now, as was mentioned by someone else, if you upgrade tires and have significantly more tire than you need for the weight you are carrying, you may want to inflate based on the weight and manufacturer inflation charts which is what is recommended for all motorhomes.

The only way to absolutely know the correct tire inflation pressure for motorhomes and heavier trailers with upgraded tires is to have the RV weighed with each wheel position on a scale and then use the weights and manufacturer tire charts to determine the correct inflation pressure.  You use the highest weight on the axle and then inflate all tires on the axle based on the highest weight.  And yes, Michelin and Goodyear both recommend increasing the pressure 5 - 10 psi (500 pounds for Michelin and 300 pounds for Goodyear) over the chart rating (weights are taken in a static, level situation, and the increase allows for weight shifting side-to-side during driving conditions, but in no case should the cold inflation pressure exceed the maximum on the sidewall.  It is true that over-inflation is better than under-inflation, but that means "for the weight the tire is carrying" and you should not inflate beyond the tire's maximum pressure per the sidewall.

Again, for your trailer, it's easy.  Run the maximum inflation pressure on the sidewalls of the tires.  Trailer tires do a lot of scuffing in turns and when backing up, and the higher inflation pressure helps reduce some of the stress on the tires.  Couple that with the fact that most trailer manufacturers install tires that are barely adequate for the trailer's maximum weight (especially on lighter trailers), and it becomes clearer why the general rule is to run maximum sidewall pressure on trailer tires (however, there are exceptions).

Hope that helps. 

Howard wrote:

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Okay, let's not get crazy with this.  Having been trained by the RV Safety & Education Foundation who has very close ties with engineers at all the major tire manufacturers, here's the information we provided in our tire safety seminars.

For trailers, it's easy.  Run the maximum pressure per the tire sidewall and never more than the sidewall maximum pressure.  The tire pressures will increase as you drive and the tires are designed to handle those increased pressures, but don't inflate past the max sidewall pressure.  Now, as was mentioned by someone else, if you upgrade tires and have significantly more tire than you need for the weight you are carrying, you may want to inflate based on the weight and manufacturer inflation charts which is what is recommended for all motorhomes.

The only way to absolutely know the correct tire inflation pressure for motorhomes and heavier trailers with upgraded tires is to have the RV weighed with each wheel position on a scale and then use the weights and manufacturer tire charts to determine the correct inflation pressure.  You use the highest weight on the axle and then inflate all tires on the axle based on the highest weight.  And yes, Michelin and Goodyear both recommend increasing the pressure 5 - 10 psi (500 pounds for Michelin and 300 pounds for Goodyear) over the chart rating (weights are taken in a static, level situation, and the increase allows for weight shifting side-to-side during driving conditions, but in no case should the cold inflation pressure exceed the maximum on the sidewall.  It is true that over-inflation is better than under-inflation, but that means "for the weight the tire is carrying" and you should not inflate beyond the tire's maximum pressure per the sidewall.

Again, for your trailer, it's easy.  Run the maximum inflation pressure on the sidewalls of the tires.  Trailer tires do a lot of scuffing in turns and when backing up, and the higher inflation pressure helps reduce some of the stress on the tires.  Couple that with the fact that most trailer manufacturers install tires that are barely adequate for the trailer's maximum weight (especially on lighter trailers), and it becomes clearer why the general rule is to run maximum sidewall pressure on trailer tires (however, there are exceptions).

Hope that helps. 

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 The "what most think "maximum cold pressure given on LT and trailer-tires is in fact the minimum pressure needed for the maximum load up to maximum speed of tire , or if lower 99m.h. Also called AT-pressure/maxloadpressure/and in the formula I got hold of Reference-pressure.

From a document of Semperit /continental I detemined that the maximum cold pressure is 1.4 times the AT-pressure.

Most american tire makers even allow 10 psi higher then AT- pressure for LT and 20 psi for Truck tires.

Because most Trailer tires can barely carry the GAWR of the trailer together, and Special trailer tires are calculated in their maximum load for lower speed so more deflectionThey need AT pressure cold.

Better sometimes would be to use that 10 psi higher even for absolute savety.

But there are trailers that have pretty oversised tires . For instance many Airstream trailers.  For those a lower then AT-pressure is possible  with even maximum reserve .

If you hold yourselfes to laws of nature and compensate for the lower speeds wich the ST tire is calculated for , you can calculate , or better I can, a save pressure with reserve.

 

The safety margins have always been a point of contention because nobody can find that information in the manufacturer written documentation.  I wish I had a better answer on that, but I don't.  The additional psi over the chart weights is just something that has been passed on between tire engineers at both companies and the RV Safety & Education Foundation for years.  I have done tire safety seminars in which Michelin and Goodyear folks have been present, and they have consistently confirmed that information.  That's the best I can offer on that.  Yes, 5 - 10 psi can make a huge difference in the way the tires "feel", but I'm just passing along the "inside" information as it relates to safety.   

TheNewhalls wrote:

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Howard wrote:

The only way to absolutely know the correct tire inflation pressure for motorhomes and heavier trailers with upgraded tires is to have the RV weighed with each wheel position on a scale and then use the weights and manufacturer tire charts to determine the correct inflation pressure.  You use the highest weight on the axle and then inflate all tires on the axle based on the highest weight.  And yes, Michelin and Goodyear both recommend increasing the pressure 5 - 10 psi (500 pounds for Michelin and 300 pounds for Goodyear) over the chart rating (weights are taken in a static, level situation, and the increase allows for weight shifting side-to-side during driving conditions, but in no case should the cold inflation pressure exceed the maximum on the sidewall.  It is true that over-inflation is better than under-inflation, but that means "for the weight the tire is carrying" and you should not inflate beyond the tire's maximum pressure per the sidewall.

Hope that helps. 

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 Sorry, but I can't find any documentation recommending adding 5-10 psi. 5-10 psi doesn't sound like much, but my experience has been my coach rides and handles better when I inflate according to the tables without adding anything extra. 

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ChefMom wrote:

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I'm almost afraid to bring this subject up again. I thought tire pressure would be a finite thing. Apparently it is subjective with everyone doing their own thing. I need additional thoughts on how to address the fact that all of our tt tires are uniformly inflated to 43 lbs ea. (which apparently they were last season as well). After reading all advice I asked DH to inflate to max pressure as noted on sidewall. He doesn't think he should as it states 60 lbs. per and he thinks at that inflation there would not possibly be enough road contact. I'm afraid of traveling with low pressure tires. Please advise and quickly as we are traveling this weekend. Thanks so much.

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 Based on the info in this thread, we know nothing concerning your rig,  hence the best advice is,  as Howard already has stated :  "For trailers, it's easy. Run the maximum pressure per the tire sidewall and never more than the sidewall maximum pressure. The tire pressures will increase as you drive and the tires are designed to handle those increased pressures, but don't inflate past the max sidewall pressure. Now, as was mentioned by someone else, if you upgrade tires and have significantly more tire than you need for the weight you are carrying, you may want to inflate based on the weight and manufacturer inflation charts which is what is recommended for all motorhomes."

Since you did state the tires on your trailer have a 60# psi inflation max,  and you are running it at 43#psi , my concern is that you may be underinflated for the load of your trailer.  Any idea as to how using 43# psi was determined for inflating the tires?  

 

Tire inflation pressures are often a topic in the RV forums I browse in. The “he said, she said” information is more often incorrect.

Tire inflation is basically very simple for RV trailers and RV Motor Homes. That’s because they are both governed by the Federal Motor Vehicle Safety Standards (FMVSS).

Under the FMVSS vehicle manufacturers are solely responsible for setting all Original Equipment (OE) recommended (correct) tire inflation pressures. Once set they become the benchmark settings for all replacement tires. (Replacement tires must maintain the ability to support or exceed the load capacities of the OE tires).

So, the vehicle manufacturers tire inflation pressures are depicted on the vehicle certification label, tire placard and in the owner’s manual. They are the minimum pressures to be maintained. The maximum tire inflation pressure is displayed on each tire’s sidewall. There is no restrictions for using inflations pressures anywhere between the min & max amount.

For RV trailers the normal recommendations are maximum allowed inflation as depicted on the tires sidewall. Trailer tires are fitted to total GAWR without any reserve load capacity requirements. Look at your tire placard.

RV Motor Home tires are also fitted to the total GAWR but with a twist, they MUST provide load capacity reserves by inflation values depicted on the tire placard. The tire industry will not recommend going lower than the vehicle manufacturer’s recommended inflation values. Enclosed is a PDF file from a major tire manufacturer. In it you will find that not using less inflation pressure than what’s listed on the tire placard is stressed.

http://www.trucktires.com/bridgestone/us_eng/press/zip/WeighForm.pdf

Because a lot of RV Motor Homes use trucker tires, confusion is born. That’s because those tires are governed differently. Even though those tires are fitted to MHs they must be fitted to the MH with the FMVSS guidelines because FMVSS 571.120 clearly governs MH tire fitments.

Bottom line: The DOT insures that minimum safety is built into your vehicles and provides the necessary information to insure that safety continues on to all subsequent owners. Once an owner takes position of a vehicle it’s their sole responsibility to keep it in safe operating condition.

A NHTSA motto; TIRE SAFETY Everything Rides On It.

-- Edited by FastEagle on Tuesday 21st of July 2015 11:48:15 AM

-- Edited by FastEagle on Tuesday 21st of July 2015 11:49:08 AM

Cummins12V98 wrote:

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Barbaraok wrote:

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And why are you adding 5 psi? Why don't you believe the chart from the tire manufacturer for the weight that the tire will carry?

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Because that is what GY Tech Support said to do when up sizing Load range. 

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 And I even add mostly more then 5 psi when using my spreadsheets.

But use another aproach, I add a percentage reserve load to the loads you determined and calculate a pressure for that larger load.

This cources that for for instance a P-tire with AT pressure of 35 psi , the pressure can dropp about 2.5 psi before it gets in to the danger sone, where damage begins to tire.

And for a 100 psi filled tire ( G-load fi) it can even drop about 10 psi before in danger sone.

I keep it to the high side where yust no bumping and comfort and gripp still acceptable, to give it as much possible reserve for things like:

Pressure loss in time

inacurate reading of pressure or weight

misyudged loads on seperate tire.

etc, etc.

 

What American made lists intend to give is yust enaugh pressure for the load you ask, to give no damage to tire when driving the speed , the maximum load is calculated for.

But in the lower pressures loadcapacity's are given to high because of using a formula that is inadequate to laws of nature.  And natures rules always rule above rules and regulations of tire-associations and law.