How are loads calculated

 Had a question asked on an RV Forum

Mike Posted

 

Tireman9 - I've seen your posts with this "minimum inflation" statement in other threads in addition to this one, and I never was able to find documentation in the Michelin files that states that UNTIL I finally realized that the "Maximum load & pressure on sidewall" statement in their Michelin Truck Tire DataBook and Inflation Charts establishes the relationship between weight and PSI for each 5psi increment in the chart. I like to weigh our MH at least once a year because we've been making some changes to it, and our trips vary from short to fairly long with different loading as a result. Long story short, I use a simple Excel sheet to determine PSI requirements based on scale weights (it's just easier for me and I like using Excel). Well, this simple little Excel lookup routine turned into a bit of a pain until I realized that the weight increments for each 5psi increase are not consistent. In fact, they are all over the place.

The way I found this out is I was calculating PSI # for our MH's weights in two ways. One was to find the corresponding PSI for my actual scale weight, and then add 10% to the PSI, or the second way was to increase my scale weights by 10% and then find the corresponding PSI for that weight. When I compared the resulting PSI's between the two methods, they were different in many instances, but not consistently so.

So the question is why do the single tire increments vary from 140lbs to 230lbs, and the duals vary from 230 lbs. to 410 lbs. Can you explain? Does setting tire pressures really have to be this exact? And which way is correct? You would think that both would have the same results, but nah-Baby-nah.

Simple answer is, The Load formula is not linear as you can see here.

 

 

 

 

  there are values that are exponents

 

 

 

 

 

As to adjusting for Dual position there are more instructions we tire design engineers have to follow.

 

 

 

 

 

I suggest:
1. Learn actual tire loading on a truck scale when the RV is loaded to your expected heaviest.

2. Assume one end of an axle is supporting 51% to 52% of the total axle load (this estimate is not exact. This is why "4 corner weights" are preferred if you are near the load limit

3. Consult Load & inflation tables to learn the MINIMUM cold inflation

4. Add at least 10% to the inflation in #3 and use this new number for your "Cold Inflation goal"

5. Set your TPMS Low Pressure Warning level to the inflation in #3 above.


Go camping.

 

 

Setting Motorhome inflation for "Newbie"

Reading a forum post that said:

"We are moving across the United States for our FIRST trip in our 06 Mountain Aire. Don’t think that’s a great idea for a first trip, but that’s what’s gonna happen. LOL. I do not have access to a four corner scale. I do have access to a cat scale. I downloaded the Michelin tire pressure guide. From what I remember here, I take the axle weight and use the Michelin guide? I seem to remember someone saying to add 5 psi to compensate for the lack of a 4 corner scale?"

My reply:

You can read my RV Tire blog for more details for Motorhomes (but not towables)

1. If you have no scale reading follow the Vehicle Certification Label AKA (Tire Placard)

2. As soon as possible, get on a truck scale when you are at your heaviest (full of fuel, food, water, propane, clothes, people etc).

3. Using the axle load numbers: Confirm no axle exceeds GAWR (gross axle weight rating) (on placard) and the RV does not exceed GVWR (gross vehicle weight rating) (on placard). If you exceed either max weight rating you must move or eliminate some "stuff" in the RV.

4. If your weights are lower than GAWR then you MIGHT be able to lower your inflation a bit but there is some effort involved.

5. Since you will not have "4 corner weights" you will not know how much out of balance side to side you actually are. Some RVs have been found to be 1,000# out of balance on an axle.

6. I suggest at a minimum you assume one end of each axle is carrying 53% of the total axle load. You could use the 53% number to consult the Load & Inflation tables.  WARNING Michelin tables assume perfect 50/50 load balance which IMO is not realistic, so you need to calculate the individual axle end load ( divide Michelin number by 2)

7. Using the 53% load number and the calculated Michelin load number you now know the MINIMUM Cold Inflation aka MCI number. It is suggested you add 10% to that inflation number for inflation when setting tire inflation. This is your daily measured Cold Inflation Pressure aka CIP. This 10% covers you for day to day temperature and elevation changes.

8. If or when the measured cold inflation (or inflation reported by your TPMS) drops to your MCI number you need to add some air to get back to your 10% margin number.

9. I see no reason to ever bleed off pressure from your daily measured CIP unless your reading is higher than the inflation number molded on the tire sidewall. If you get that high you can bleed down to the tire sidewall pressure but never below the MCI.

Ya a bit of work but once you think about your goal - Stay above the MCI and below the inflation molded on the tire sidewall you are good to go. A TPMS makes the job of checking inflation on each day of travel much easier as you simply check each morning before you start out. TPMS will also give you a warning when or if you get a puncture od have a leaking valve and are losing air. A good TPMS will have some form of "early warning" when you start to lose a couple PSI while running down the road. This could prevent a serious tire failure.

How do I set inflation on my TV and RV trailer?

Got this PM from someone who reads RV forums.

"Good evening, I'm looking for some professional advice. I have a 2500HD pulling a fifth wheel, my steer axle is 4,000 lbs, drive axle is 5,380 lbs, and our trailer is 7,700 lbs. Tires on the TV are rated for 3,100 lbs a piece at 80 psi. The RV tires are rated for 2,800 lbs at 80 psi. Do you think I am ok to run 65psi in the steer axle, 70psi in the drive axle? What I've been doing is 75psi steer, 75-80psi drive, and 80psi trailer. Our TV tires are Michelin MS2 LT265/70-17 the load range chart says I can run much less psi. Also, our trailer tire's are Maxxis 8008 225/75-15 LR E, also the load range chart shows I can run less psi. Any thoughts on what you would do would greatly be appreciated, thank you. New Crusader owner"


To start with it is important to remember that we should never operate tires with inflation lower than what is needed to support the actual load on the tires.
As I have pointed out in my blog we first need to confirm the actual load on our tires. For TV we will find the side to side loading is usually 49/51 to 50/50 split so we can take the measured axle loads divide by 2 and then use the resulting figure when consulting the Load Inflation tables for our size tire.
I have links to many load/inflation tables and related info HERE. Once you find the MINIMUM inflation, I suggest you add at least 10% to that number to allow for day to day variations. Having said this, it is important to remember that the car company spent a lot of time and money evaluating many different tires at different pressures to arrive at the recommendation that is on the Tire Placard on the driver door jam. You should note that the Placard inflation may be higher than my above-suggested calculation as my calculation is only addressing load and not handling, braking or the fuel economy.
The scale weight for the TV for the above needs to be the reading with the RV & TV fully loaded as heavy as you ever expect to tow.

The RV tire inflation is different. Due to SIDE LOADING in trailer application, I strongly recommend running the tire sidewall inflation as your CIP. I think that if you review the RV Placard info from the RV company you will also find that they say to use the inflation number on the tire sidewall.

I know you were hoping I would just tell you to run xx psi here and yy there and zz on the trailer but without knowing tire sizes and Load Range for all your tires, I don't have enough info to provide an informed answer BUT I feel you now have enough info that after reading the sidewalls of your tires - Be sure to check each as they might be different on TV and RV and possibly even different F & R on the TV - You now know how to establish the correct inflation for your current vehicles and for any vehicles you own in the future.

I hope this information and instructions help. If not you can always contact me directly using the email under my video picture to the right.

How much inflation in my tires? Question from new RV owner

Recently read yet another forum post on the topic of "How Much inflation should I run. This post followed the standard format of:  A. I just bought an XXX RV. How much air do I need in my tires?  B. Numerous replies ranging from "I use xx psi" to "You must always run the pressure on the tire sidewall"  to the more correct reply of "You need to know your tire loads first". Some forum threads run to dozens of back and forth exchanges Some have correct info IMO while others are still using what I consider "Old Wives Tales".  I recently replied as follows.



1. Almost all tire Inflation/Load charts have identical numbers (maybe as high as 98% )so if you can't find your brand you can reasonably use another brand till you do.

2. Yes, the charts give the MINIMUM inflation needed but to avoid the need to adjust your inflation every morning (inflation changes by about 2% for every change of 10F) I and others suggest you add a bit so you are running the minimum + 0% to + 15%.

3. You should NEVER run lower than the minimum inflation shown on the chart.

4. Since all tires on any one axle should have the same CIP (Cold Inflation Pressure) you base the minimum on the heavier end. This is why we recommend "4 corner weights" to learn what the heavier end load is. Until you learn the actual load on the heavier end you can assume one end is supporting 53 to 55% of the total on the axle (the axle weight when on the truck scale).

5. How much to add over the minimum? I think you will find various suggestions in the range of +1 psi to +10%. Since I am offering advice to a wide range of users (ST trailer tires, LT and Class-A) with minimum inflations from 50 to 120 I prefer the percentage and if people want to have their CIP ending in 0 or 5 they can add the % then round up. ( Note the +1 Psi is from Tire Rack where they are advising owners of passenger tires that normally are running 30 to 36 psi)

6 Premature wear. Most LT and 22.5 size tires can be good for 60 to 100,000 miles wear so most RV owners will have their tires "age out" before they wear out so the minor wear difference, if any due to running + 5% over the minimum if overshadowed by variations in suspension wear, alignment variations, and driving habits. The center shoulder wear info is based on car wear rates primarily with bias tires or inflation differences greater than +/- 15% from the suggested CIP.

7. "Correct" inflation is not what the charts say. They are providing the "Minimum" cold inflations is every case.

8. Adding Load % and adding inflation % is done only to compensate for not knowing the actual heavy end of an axle. If you learn the actual heavy end when the RV is fully loaded to the heaviest you ever travel at, I do not suggest you need to add any more weight when doing your calculations. How much can you be out of balance side to side? I have seen a very small % of RVs with the load at 50/50 side to side. Most appear to be in the 53/47 to 55/45 range but a few have been found with over 1,000# heavier on one end.

9. It is important to realize that when we look at actual weights of RVs in use, over half exceed one or more of the weight specifications for tires or axle loading. IMO this is a clear indication of why so many RVs have tire problems.

Another example of pressure and TPMS setting calculations

David said:

"I am a newbie. Just 5 weeks with my 2017 Newmar Bay Star 3113. I need some help understanding just what would be the correct or appropriate tire pressure on my coach. When loaded with my wife, dog and self, partial food and clothing, tools, chairs, BBQ ladders, 2/3 water, full gas and propane and misc stuff I got the following from the CAT scales: Front axle - 7,300. Rear axle - 13,260.

Here is my dilemma: The dealer delivered the coach with about 85 lbs. per wheel cold, but when I use the Michelin tire pressure chart for my 235/80R 22.5 XRE tires they should be just 75 lbs! I am concerned that they will be "underinflated" and could build up excess heat. Should I keep the 85 lbs. or lower the pressures?"


My reply:
David, Welcome to RV fun.

For all things tires (except buying) I obviously suggest you check my blog. I don't expect folks to remember everything but if you spend a few minutes checking it out you will learn how to use the "Label List" on the left to find a post of the topic of interest. There is also a search box in upper left.  Now to your specific question.

1. We want to know the heaviest load on your tires and since few RVs are perfectly balanced side to side for weight we ideally want to know the "4 corner weight" to learn the heavier end for each axle. Lacking knowing that number, IMO, we can do a rough calculation by using 53% of the axle scale weight for the RV when it was fully loaded (the expected heaviest it will ever be).

2. 53% of your front would be 3,870# and rear would be 7,030# or 3,515 on each dual.

3. Looking at the Michelin load tables we find for your size at 85 psi can support 3,975 for single (front position) and 80 psi supports 7,050# for two tires in dual position.  Yes, we always round up.

4. Based on the above, your MINIMUM inflation would be 85/80. This is the number I would use for the low pressure warning numbers on your TPMS.

5. I recommend adding 10% and again, rounding up, that means 93/88 psi for your Cold Inflation Pressure or CIP. In your case, given the close numbers for the front load, I would be comfortable using 90 psi all around, as a single number is easier to remember. This 10% gives you a nice cushion so you do not have to chase your tire pressure around whenever the temperature rises or falls. You could even get down to 85 psi before needing to "top off" the tire pressure again.

6  All tires on an axle should be inflated to the same level for improved handling and response in an emergency situation.

7. I would set the TPMS High Pressure warning to 110 to 115 psi and your high temperature warning level to 160 F.

8 Remember CIP means when tires are at ambient temperature and have not been in direct sunlight or driven on for at least two hours.


Finally, in your case, you are close to some numbers when we round so if your RV is more balanced than my suggested 47/53% you may be able to lower my suggested inflations by 5 psi, but only when you confirm your heavier end is less than 53% of the total.

##RVT794

Am I reading Load & Inflation tables correctly?

Wayne M. asked

Tireman, Here is some information on my Toyo 265/75R22.5 LR-G tires. Can you confirm I am reading the tables correctly?
Toyo 265/75R22.5
PSI     70     75     80     85     90     95    100    105   110
Dual 3625 3705 3860 4040 4205 4410 4525 4685 4805(G)
Sing 3875 4070 4300 4440 4620 4805 4865 5150 5205(G)
Measured scale weights on each corner
RF: 4650        LF 4750
RR: 9000       LR 8250
Right side has Refer. There isn’t anything in the bays (not all the way through bays) that I could possibly switch around for even distribution so I have to go with the heavier weight.
I’m thinking 100 psi for the front.
What would my rears be with a fudge factor?
++++++++++++++++++++

First off , I have to thank you for providing the information on your specific tires and your actual tire loads for each end of your axles. I prefer data to guessing.

With 4,750# on the heavy end of the front axle we see that 95 psi can support 4,805 so that would be the MINIMUM Cold Inflation Pressure for your fronts (remember all tires on an axle should have the same CIP) and I suggest you add 10% (10 psi) cushion to get 105 psi CIP on the fronts.

The rears are dual, so looking at those inflations.  9,000 divided by 2 gives 4,500# per tire, with the 90 psi being the minimum inflation needed to support the measured load. Adding 10% or 9 psi gives us a suggested 99 psi. 100 is easier to remember and measure so lets go with 100 CIP on each of the 4 rear tires.

Comment: Please always adjust inflation up and avoid going down no matter how close the weights are.

##RVT786

When is Minimum inflation the Maximum inflation?

Sometimes the information on inflating tires can lead to some confusion.  OK a lot of the time it can be confusing to many.

As many of you know I try and follow a number of RV forums and offer comments. I try and focus the comments to correcting serious or significant errors or misunderstandings, especially when Safety Related.

Recently there was some confusion about the Maximum allowable inflation for a tire. Some wanted to co-mingle some information from PSR or passenger car tires with information about large TBR, truck bus radials. The discussion then went way off track. Rather than limit my audience to those following that thread, I decided a blog post would be more appropriate. Also I wanted to be sure to have all the information up to date and accurate I contacted an "old friend" from the tire industry and he sent me this nice summary. With his permission I re-print it here.

First some definition of terms may be appropriate as "tire engineer speak" may confuse some.

"Seating pressure" this is the inflation needed for the tire beads to "pop" home against the wheel/

"FMVSS" these are various Federal Motor Vehicle Safety Standards. If you need some reading that will put you to sleep HERE is a link offered by NHTSA.

 "NHTSA" NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

"PSR"  Passenger steel belted radials or the normal tire you find on todays cars

"TBR" Truck Bus Radial  as found on most Class-A RVs

"LTR"  Light Truck Radials 

"CIP" Cold Inflation Pressure

OK here is the nitty-gritty

"First, the max pressure to seat beads as a matter regarding the technician’s safety is 40 psi, whether passenger, light truck, or truck-bus.  This bead seating pressure is totally independent of the tire maximum operating pressure.

It is important to clarify the differences in sidewall markings of the tires you bring up:

PSR & LTR Tires (load range E or less):  Since FMVSS 139, these tires have sidewall markings indicating maximum load AND maximum pressure.  Maximum load means max [static] load, and maximum pressure means max [operating] pressure (cold).  With respect to the minimum pressure that carries the maximum load there is a difference:

·         Passenger Tires:  These tires are usually marked with a maximum pressure that exceeds the pressure necessary to carry the maximum load marked on the sidewall.  For example, the tire may be marked with 44 psi max pressure, but only requires 35 psi to carry the max load.

·         Light Truck Tires (load range E or less):  These tires are usually marked with a maximum pressure that is also the pressure required to carry the maximum load.  For example, a load range E tire marked with max 80 psi would need that same pressure to carry the max load.

TBR Tires (and light truck load range F and higher):  On these tires the sidewall markings indicate maximum load AT a certain pressure (the word “maximum” is not used in regards to pressure).  Maximum load means max [static] load, but the pressure is not the maximum operating pressure (cold).  This marking just follows FMVSS 119.  Essentially, the pressure marking is informative, simply telling the reader the pressure that is required to carry the maximum rated load.

However, for most practical purposes, on TBR tires the pressure marking is typically considered the maximum pressure recommended in the tire while in ordinary service.  Certain situations may permit cold inflation pressure higher than the marking, usually in consultation with a tire manufacturer for a specific product, application, and service.

Regarding load-inflation tables:  As long as you are looking at the right table, this is where you find the pressures needed to carry certain loads for a given tire type, size, load rating, etc.  Note that for truck-bus, you might need to make sure the tire is a “T&RA tire” or an “ETRTO tire” since the tables can differ, even though the size codes are the same (such as 295/75R22.5).  Also, a tire manufacturer may have unique load-inflation table(s) associated with certain tire models, sizes, etc.

If an operator is running at max load, and the pressure to do that happens to be max pressure, then yes, they need to be diligent.  But it is manageable, and they owe it to themselves and to others on the road to do so.  Pressure loss through permeation requires minimal adjustment approximately once a month.  For predictable swings in temp, set the pressure when it is likely the coldest, and try to consistently check it during those times, such as early in the morning before setting out.  No one is saying that everyone in all circumstances needs to set pressure to +/- 0.1 psi every morning, noon, and night with three hours of ambient cold-soaking before taking measurements.  I agree with you about reducing load; not just due to the tire influence, but also drivetrain/axle and chassis wear and tear, braking performance, fuel economy, etc."

So we see there are similar but different words on the sidewall of tires. Some have a stated Max cold inflation others do not. This is one reason why it best to have tire service done at a store that has the appropriate equipment and training to handle safe and proper mounting and inflation of the type tires you are working with. This does not mean you can't add 5 or even 10 psi to your tires but IMO if you need more than 20% of the CIP there is something wrong and you really need to consider having a professional inspect and re-inflate your tires. Inflating an improperly mounted, improperly repaired or damaged tire can injure or even result in death if not handled properly.
OK now back to our regular programming.
One other comment I have is that many times some think tire failure "Blowout" is caused by too high a pressure but this is essentially incorrect. Unless you have damaged the body ply cords, be they Nylon, Polyester, Steel or Rayon by over flexing and running significantly under-inflated, tires are designed to tolerate the normal pressure increase seen when running highway speeds at the approved load.

But if you have damaged or run the tires in overload or under-inflated for the actual load or perhaps at a speed higher than the tire rating you may have damaged the cord sufficiently that it has lost a portion of its strength so in that case even normal cold inflation may be too high. This is one reason any tire that has been damaged must be rendered un-usable or if it appears to be OK then inflated in a Safety Cage.


++++++++++++++++++++++++
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Links to Load Inflation tables

Last updated May 25 2025   (TOYO Info)

Almost all tire companies follow similar load formula calculations in the USA, Europe and Asia. BUT minor differences occasionally occur due to doing calculations in inches and pounds vs millimeters and kilograms as there is rounding that takes place along with some minor differences in some "K" factors. Also some sizes have been around for decades so their load capacities may not match the formulas exactly but are just accepted as acceptably close. So there are minor variations. This is why it is best to use the tables published by the company that makes your brand of tire.

Sometimes this is easy because you use one of the big name companies such as Goodyear or Michelin while other times you may find you have tires that are not actually made by the company with the name on the sidewall but are in fact just imports made in common molds with changeable nameplates.

This post will be updated when I learn about a company posting load inflation tables for their line of tires.  If you find an error or omission, please drop me an email (address under my picture on the right) with the link that needs correcting or new link and I will update this post. That way you can bookmark this page and save it for future use.

I plan on listing the links base of alphabetical list of the tire company name.
To the best of my knowledge Both Goodyear and Bridgestone/Firestone follow the Tire & Rim Association (US) published tables so you can simply look at their tables for the numbers if you can't find your tires in any of the links below.
+++++++++++++++++++++++++++++++++++++++++


If you find a broken or bad link please send me an email so I can fix it. Thanks.


Bridgestone\Firestone
Links to Load Inflation charts, How to Weigh your RV worksheet and related material. Note Bridgestone "Medium and Light Truck data Book includes Load inflation tables for 16" and larger tires for both Bridgestone and Firestone brand tires.

Carslile  Has product info and size list but no Load Inflation tables However since they only have ST type tires which I suggest always be run at the inflation pressure molded on the tire you can use the max load info to confirm you are running under the tire max by at least 15% for longer tire life while still maintaining the tire max inflation. They do have three larger size ST type tires found HERE

Continental
Databook for commercial tires 

Cooper  Does not publish Load & Inflation tables. I suggest you use Bridgestone or Goodyear tables

Double Coin truck tire
Load & inflation for 19.5" and larger


General truck tires
Load Inflation tables

Goodyear
RV tire information including link to Load & Inflation tables

Hankook Medium-duty Truck tire info. The link will download their catalog with Load & Inflation info.

Hercules  Does not publish Load & Inflation tables. I suggest you use Bridgestone or Goodyear tables. BUT their high load ST tire info can be found HERE

Kumho
Product info page and links to their technical information.
Note they show both P-metric and "Euro-metric tires that do not have a P prefix but based on the inflation these are basically passenger type tires even though some are listed under "Light Truck". Only their "Road Venture has actual LT type tires listed.  They do have 19.5 and 22.5 size tires.


MAXXIS LT tires
Tire data on LT tires but no Load Inflation tables. I suggest you use Bridgestone or Goodyear tables

MAXXIS Trailer tires
Tire data on ST tires but no Load Inflation tables. I suggest you use Goodyear tables

MAXXIS Trailer Load & Inflation tables

Michelin
RV Tire guide and links to Reference Materials and Load Inflation tables for 16" to 24.5" tires in RV application. NOTE many of the Michelin tables are not based on single tire loads but axle loads so you will need to divide the Michelin numbers by 2 for Fronts and by 4 for dual position individual tire loading. This just adds a bit of confusion to your calculations. I also am aware that a number of Michelin tires do not follow the US TRA tables so if you are using Michelin brand you really do need to use their tables.  16" and other size Load Inflation tables can be found HERE

Omni-Trail
This importer is offering 75 mph speed rating on these ST type tires.

Sailun   S637  17.5 size Tire information  Load & Inflation tables.  Here is info for their ST637T   ST type tire

Sumitomo you can download their booklet on Medium Truck size tires for 19.5 & 22.5 sizes
Load Inflation table on pg 4

Towmax  does not publish tables only the tire max load.

TOYO
Toyo changed their web site so you will need to go to Goodyear or Bridgestone for up to date inflation tables

 Trailer King has tire spec sheet shat show the max load and required inflation HERE.

 

Uniroyal LT size info. They say to use the Michelin Load & Inflation tables. "It's important that you get all the safety-related materials that come with the purchase of new Uniroyal passenger and light truck tires. If you did not receive a warranty book, you can download one at www.uniroyaltires.com/care. If you did not register your tires, please take a moment to do so at www.uniroyaltires.com. Registering your tires is easy and takes just a minute."

Yokohama   
Info on their commercial tires on pg 23 HERE.



=========================
 Others will be added when the tire company responds to my request for a link, or when someone lets me know about a link.

.

General information

How to read a tire Load Inflation table
Barry's Tire Tech

National Highway Traffic Safety Administration
Tire Safety

File a complaint about a tire failure with NHTSA

Air Pressure, Temperature variation
Tire Rack      
or go HERE

Passenger tire inflation w/video

The Tire & Rim Association. Where to buy Industry Standards books


MasterCraft tire Education


Rubber Manufacturers Association
Links to Tire Safety information

RV Safety Education Foundation
RV education and tire weighing service

BigRig
Truck Scales

CAT Scales
Truck Scales

FifthWheel
General information and weight calculations for trailer owners


Please send me an email Tireman9   at   gmail.com   if you find one of these links is broken. Thanks


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##RVT803 (updated 7/2017)

Minimum or Maximum inflation or Load...I'm confused

Read a post of an RV forum from a motorhome owner who was a bit confused by the wording on his tires about Max Inflation and max Load when some people are telling him to learn the minimum inflation. He said
"Uhh.... So why does it say MAX PSI in front of it???  MAX means minimum???"

My answer:
Yes this is confusing.  The intent of the information is to let you know that when you inflate the tire to the pressure associated with the highest level for the Load Range it is rated to carry the stated load and no more.
Remember that "Load Range" is a replacement for the outmoded "Ply Rating"

When you look at a Load/Inflation table you will see a series of inflations in 5 psi increments. You will also see a series of load capacities.

I'm going to use a LT size but the same process would be used by other Motorhome owners.

Size LT225/75R16
Single  1790#@45  1940@50   2060@55  2190@60  2335@65 
2440@70  2560@75  2680@ 80  3000@95

Now the other bit of important information in the table is the Load Range limits for this size tire.  LR-C is 50psi  LR-D is 65  LR-E is 80 and LR-F is 95

If you had this size tire and it was a LR-E tire it would say 2680# at 80 psi Max or some such

Note some tire companies use the wording like 2680# Max at 80 psi Cold or some variation thereof.


The inflations in the table can be considered a Minimum when you start by looking at your measured load.  In the above example if you measured 2500# on the heavier front tire you would select the inflation from the table associated with at least 2500#  which means 2560# and you would then know that the Minimum cold inflation you should ever run was 75 psi.

Finally we know that pressure varies as the ambient temperature changes. This change is about 2% for every 10°F increment so to avoid having to chase around looking for a service station every time the temperature drops 10°F, I suggest you add 10% to the required inflation level which in the case of this example would be 7.5 psi

I wouldn't worry about getting the inflation to the exact 1/2 psi just know that if you add 7 or 8 psi to your minimum of 75psi you are good to go. You also don't have to worry about adding air if it gets cold and the inflation drops to 79psi as you have a nice margin built in.

Over time all tires loose air pressure so eventually your pressure will drop to the point that your day to day pressure variation will result in you having only 75 psi in the tire. I would not wait till your margin has been used up but would have added a bit of air once I got down to 77psi or so and bumped it back up to the 82/83 psi level.


Long explanation but I wanted to give you the background so you would understand why I say

1. Weigh the RV
2. Select the minimum cold inflation for your tires based on the table minimum inflation
3. Add 10% margin to that inflation to learn your "cold set pressure"
4. Inflate all tires to the inflation for the heaviest loaded tire on that axle. (all tires on each axle should have the same inflation)
5. Check your inflation in the morning before you travel more than 1/2 mile and before the tires are warmed by sunlight or monitor the inflation all the time with a TPMS.


Hope this helps.


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Real quick post on considerations when changing tire type or Load Range

When changing the "Type" tire be it P-metric, LT, Euro-metric or Euro Commercial or ST or even Low Platform trailer you MUST consult the appropriate Load \ Inflation tables  AND when passenger type tires are involved make the required load adjustment based on the type vehicle you are looking at.

While the vast majority of tires use the same Load/Inflation tables there are a few exceptions. Usually Michelin but also some ST tire brands have Load & Inflation numbers that are a bit different that the rest of the industry. Some ST tires even has special ratings that are not published but are covered by a special dispensation letter from NHTSA so reviewing the original Loads & Inflation for ST tires and comparing to the Tire & Rim tables or tables from other companies such as Goodyear, Bridgestone\Firestone or MAXIS are in order. In my experience these companies seem to line up 100% of the time with Industry guidelines. If your numbers are anything different that means you MUST do more investigation or face the posibility of being in an overload situation and not knowing it.

It's not hard to do but you do have to make an effort to cover ALL the requirements. While most of the info you need is covered in the Load/Infl tables some considerations such as speed rating limitations and "De-Rating" of the load capacity are things that even many tire dealers are not trained to do so you do need to consult a knowledgeable source.

Please remember that probably 90% or more of tire applications do not involve a change in type or application so the above is definitely NOT the norm even for the folks on the 1-800 Customer Support lines.



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RV tire reference links. Load / Inflation tables etc

Based on posts I see on various RV forums it appears that some RV owners are having difficulty finding the appropriate technical information on their tires. As a result sometimes they post questions such as "I have a XYZ RV with ABC brand tires what is the correct inflation for my tires". If you are a frequent reader of this blog I trust you can see that much critical information is missing and any answer that says "Use QQ psi because that is what I use on my RV" is not much better than a wild guess.

I have decided to assemble links to tire Load & Inflation tables for the "major" brands of tires likely to be found on RVs. Now I know that there are many tires out there that are not made by or for the major tire manufacturers that have been selected by the company that assembled some RVs so this is not a list of each and every tire out there. If you have a tire not identified from one of the manufacturers I have listed, please send an email (address posted in the About Roger info on right side of this blog) and I will endeavor to update this list. Unlike most blog posts I plan on updating this post when new or additional information becomes available so you might want to Bookmark this page to your list of Favorites.

Note: I will use the term "TBR" for Truck Bus Radial and this in general means tires with 17.5, 19.5 and 22.5 rim diameter. "LT" of course means Light Truck and "ST" stands for Special Trailer. "P" or Passenger type tires would only be on passenger vehicles or very small trailer.

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Sometimes it is difficult to know who actually made your tires. I have seen tires with the brand name "GT" which is obviously not the name of a tire company but simply a name used for marketing a line of tires. If you do not know who or where your tires were made HERE is a web site that will allow you to use the first two characters of the DOT serial molded on the tire sidewall to learn the facts. For example if the DOT serial on your tire was   4DHLABC4513  you would look uo the "4D" and discover the tire company to be BRIDGESTONE/FIRESTONE NORTH AMERICAN TIRE, LLC.  and the plant location to be Morrison Tennessee, USA, with a manufacturing date of 45th week 2013 or the week of Nov 3 2013.
If the first two characters were  4V you would discover the tire company was actually CHONCHE AUTO DOUBLE HAPPINESS TYRE CORP., LTD, TAIYUAN CITY, SHANXI, China.

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Bridgestone RV application info.
While this company does not appear to actively market to RV owners they do have tires that will fit and work on many types of RVs that use LT or TBR type tires. This web page has general information on RV applications and a "how to guide" to help RV, travel trailer, mini-bus, van, light truck and ambulance owners learn how to properly weigh their vehicles and maintain their tires". The page also has a worksheet to help owners to properly weigh and calculate the correct minimum inflation needed for their unit. Much of the information on the web site is general in nature so is of value to many RV owners. Here is the Load Inflation chart in download PDF format for RV size tires made by Bridgestone. This brand is sold and serviced through both company stores and independent dealers.


Continental USA
This company has a line of smaller "commercial" tires based on European designs aimed at the Utility/Van market in addition to both LT and larger TBR size tires,  Some of these tires might fit trailers including larger 5th wheel trailers and come in 14", 15" & 16" rim diameter. NOTE these tires have sizes like 225/70R15C LR-D. The "C" after the rim diameter stands for "Commercial" and is a European background. Do not confuse these commercial tires with LT type. The sizes may be similar but the loads,  inflation and even some of the dimensions are different.
TBR size Load Inflation tables starting with 17.5" diameter can be found here. 
LT & European Commercial type tire Load Inflation 


Dunlop is a subsidiary of Goodyear Tire & Rubber Co.
They have a selection of LT type tires. This brand is sold and services through both Goodyear company stores and independent dealers. I could not find Load/Inflation tables specific to Dunlop but would expect that the Goodyear charts should line up 100%.  

Firestone is a subsidiary of Bridgestone Tire Co.
Like their parent company, Firestone does not actively market to RV owners. They do have their own line of LT and TBR type tires. You can download their Data Book HERE. This contains technical on both current and many discontinued tire lines along with numerous pages of tire, wheel and vehicle technical and safety related information. Load / Inflation tables for Firestone brand tires can be found in both the Data Book and downloaded separately HERE. They also have a page of general tire information and links HERE.  This brand is sold and services through both company stores and independent dealers.


Goodyear
This company actively markets tires to the RV community is ST, LT and TBR type tires. They have a web site specially designed for RV owners with numerous links to pages with supporting technical information on "Tire Selection" and "Care & Maintenance". They have four videos featuring a now retires tire engineering friend of mine, Tim Miller as he explains various concepts of proper tire use and care in the RV market. I definitely recommend that everyone in the RV community watch these videos. If you want you can go directly to their Load & Inflation tables and learn about your tire capacity if you have this brand.  This brand is sold and services through both company stores and independent dealers.


Hercules
This smaller tire company has a line of tires for RV application covering  LT and TBR application. I find they have a number of heavy duty LR-G and LR-H tires in 16" and 17.5 diameter that may solve some heavy load issues that some RV owners seem to struggle with. These tires are sold through independent dealers and I could not find any company owned store information of on-line Load/Inflation information. Info from them indicated "Hercules Tire follows the guidelines published by The Tire and Rim Association. " so you can look at the tables used by Goodyear, Bridgestone, Firestone or Michelin.


Maxxis
This company was founded in 1967 and has a variety of different type tires. For the RV market they focus on ST and LT including small commercial type tires. You can review their web info on ST type tires including their Load Inflation tables HERE.  The information on their Commercial and LT products can be found HERE. I do note that they have a 5 year warranty on their trailer tires unlike many of their competitors that have only 12 month or less. These tires are sold through independent dealers and I could not find any company owned store information


Michelin
This is one of the two major tire companies that focus on the RV Motorhome market. Their Load/Inflation numbers are sometimes confusing as they sometimes show the load for a axle rather than individual tires so it is very important that you read the numbers and table headings closely. Remember when selecting the inflation needed for your tires based on the actual load you need to select the loads on the heavier end of the axle. All tires on an axle should have the same inflation (i.e. based on heavier end) and you still need to add at least 10% to the minimum inflation specified for the load for your Motorhome. While most of the inflation ratings are the same as seen for Goodyear or Bridgestone there are a few exceptions so this is another example of you needing to confirm the ratings of the tires IN WRITING before you make your purchase. 
You can find general information on Michelin RV tires HERE. There are links to Load & Inflation tables HERE.


Private Brands
Many of the smaller tire companies are in reality just "Private Brand" marketing companies. They do not design, engineer or manufacture tires themselves but simply place large volume orders from other manufacturers. Many times these companies can offer lower prices since they do not have the overhead of design or testing staff and facilities but this means that if you are trying to get technical information form the company you may end up talking to a "customer service" person with no actual tire experience. They also do not have company stores so if you have a warranty claim you may have to return the tire to the location where you made your purchase or sometimes it will be your responsibility to ship a failed tire to some service location many states away.

Private branding is just a marketing plan and is sometimes used by Major companies. Goodyear makes and sells Kelly brand tires. Firestone made Dayton brand. This is why it is important for you to read the DOT serial to learn who really made your tires. In some cases a marketing firm may have one size made by tire company ABC but a different size made by company XYZ. Other times the marketing firm might have 10,000 tires of a given brand and size made at one location but the next batch could be made at a completely different location or tire company. This "flexibility in manufacturing could man that the performance or reputation of a "brand" of tires may depend on which size or even what date of manufacturer we are talking about.

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Trailer Owners need to remember that they need to run the inflation on the tire sidewall to minimize the damage done whenever turning. You can refresh your understanding by reading THESE posts.

WARNING to Trailer Owners.
For the most part you will find that brands not listed here will follow the US TRA published Load Inflation tables as used by Bridgestone, Firestone & Goodyear.  BUT I have run into a few instances where the RV trailer assembler and the tire distributor "played games" and have adjusted the load capacity upward just enough to meet the legal requirements for the GAWR to be equal or less than the total capacity of the tires. These loads are not in the Industry Standards and means you are stuck with the size, LR and brand tires as supplied by the assembler or you will not be able to carry the load specified in the owners manual or on the placard affixed to your trailer. This is one major reason why you should ask to see the tables for your individual tires and compare them to the industry standards otherwise your tire replacement options will be limited to a single tire.





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