Clarity is needed on a question about "consumer grade" tires.

 Here's another question on tire inflation and "ply rating" on an RV forum, and an example of a "failure to communicate." This one is a bit complex as the person asking the question about tires has an F-150 and wants to be sure his tires are "good enough" for his plans.

Hi. I have a 2022 F-150 with 20-inch tires. The tires seem to be "consumer grade" 4-ply tires. I have a relatively light Real Lite SS-1600 that weighs in at about 1200 lbs. dry. I've read somewhere you need E-rated tires, which are 10-ply. I'm taking about a 2-month trip on this rig this spring. Do I really need to replace my almost-new tires?

I assumed that by "consumer grade 4-ply tires" he meant the standard "P"-type tire that would probably come standard on an F-150. Based on that assumption, my initial reply was:

Tires are rated to carry a certain load and the max load capacity is based on the tire inflation. You need to confirm your actual tire load by going to a Truck Scale. Many truck stops have scales. You can check Google for "Truck scale near me."

The "dry weight" of your RV is not important unless that is how you will travel, that is, with nothing in it. You need to confirm the weight on the trailer tires AND the load on the F-150 tires with the trailer fully loaded and hooked up as you intend to travel when "camping." Again, you need to get on a scale as you cannot estimate the weights by looking at the F150 or the trailer. Once you learn your actual weights you can consult tire Load & Inflation tables to learn the MAXIMUM load capacity and minimum inflation required for your set-up and your tires.

The rest of the story

Then the next day we learned "the rest of the story":

The "RV" he was talking about was a "slide-in" camper for the bed of his pickup. This confusion and the delay in getting an answer shows the importance of providing all the appropriate information about your RV and/or tow vehicle when asking a question the first time. Not everyone is familiar with the names of all the different models of RVs in the market. This results in a waste of time of the people reading the initial question if you do not include all the appropriate and needed information about the RV or your tow vehicle, or your tire type, size and load range.

Anyway, after learning that we were talking about a camper that slides into the bed of his pickup, I pointed out "if your truck load capacity is 1716# and the camper weight is 1200# when empty, that only leaves 516# for you, your passenger, clothes, food, water and camping supplies. Even increasing the tire pressure to their maximum will not increase the F-150 load capacity above the 516#. You will be very tight on what you can carry and even changing tires may not solve your problem. It is important that you not exceed the GAWR for the F-150 vehicle as increasing tire capacity will not increase the GAWR.

It's now been over a week since our camper asked his original question. Despite there being 43 posts, he still doesn't have an answer to his original question.

 

 

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How many "Ply" in your tires?

 Here is a picture and comment I found on an RV Forum. I suggested that the owner review his understanding of tire construction and that he read the material list that is molded on the sidewall of all tires. The failed tire does not have 12 or 14 "ply". I also pointed out that it does not appear to have a "ply" of Nylon over the steel belts.

  Do you know how many "ply" or layers of which materials are in your tires?

The owner said "After many problems with ST 12 ply I have moved to "xxx" brand 14 ply and no more problems. I drive to Mexico and back every year 9,000 mi."

I pointed out the problem with thinking that there were actual 12 or 14 "Ply" in the tires as that term lost its meaning when tires were switched from "Bias" or "Diagonal" to "Radial". I strongly recommend that ST type tires include Nylon or similar material as "Cap Ply" over the steel belts. This can help lower the Interply Shear stress forces found in tandem axle trailer applications.

If you do not know what Interply Shear is then I suggest you review this post. 

The tire failure probably had a contributory cause of impact damage from the poor roads in Mexico. 

Here is my post on the scientific study of impacts and tire failure showing a 100% correlation.

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Is a 10 ply tire better than a Load Range E tire?

 Had a question:

I've read many comments on various RV forums about truck tires vs. "motorhome" tires as it pertains to cost.  Some also mention the firmness of the ride as one of the comparison differences.  Upon reading several tires' specifications I've seen that some have 16-plies ( for example: Michelin xza2 energy 295/80r22.5) whereas others have 18.  This leaves me wondering if the number of plies can help predict ride firmness?  

Does the advertised number of plies refer to the sidewall or to the portion of the tire that touches the road surface? (I'm guessing these can be different.)

Also, what other factors and/or specifications contribute to a tire's ride firmness that may help us compare them?

 

 My reply:

When people talk about the "ply" they are usually referring to the sidewall as the number of layers under the tread is always more as there are usually two to four or more additional layers under the tread of radial tires.

I suggest you read the tire sidewall of your motorhome tires. I believe you will see that those tires say something like "Sidewall 1 Ply (or layer) of steel".  The use of "ply rating" in advertising is just perpetuating the confusion that started in the 70's with "Ply rating" such as "6 for 8"  or even "8 for 12" when better and stronger cords were introduced in Bias truck tires. 

With the switch to radial construction, you will find that most radials from car to light truck and even heavy truck have just one "ply" or "Layer" in the sidewall. The letters for "Load Range" replaced the "ply rating" advertising because some people don't understand the concept of "rating".  When you are looking at large radials with "Load Range" of F and higher all that those letters are telling you are the inflation level the tires can tolerate. 

If you look at the published Load & Inflation tables you will see that some sizes are available in a number of different Load Ranges.

While these are LT tires they show both Inflation, Load Range and Load rating.

 

 

Here you can see that some sizes only come in one Load Range while others come in many. You will also note that a Load Range C, D, or E are only rated for the same number of pounds if the Inflation is the same.

One tire I designed was a Load Range E version of a Load Range D tire and after running all the required tests it was discovered that for this specific tire I only needed to change the number of strands of wire in the bead area (where the tire attaches to the wheel) to meet all the strength requirements. So you can see that it is impossible to make a broad statement on the tire construction to provide any useful information on the possible ride qualities of two different Load Range tires.

If you were to conduct a controlled ride test of 295/80r22.5 size tires with different Load Range but ran the same inflation level you would not be able to feel a difference in ride. However if you were to change the inflation level to achieve greater load capacity you might feel a difference but in that case wouldn't you expect a heavier loaded vehicle to have different "ride"? 

My original question in the title of this post is intenionally misleading as you will find that the load capacity of a "10 ply rated" tire and a Load Range E tire of the same size from the same drsign are really identical.

##RVT1045

Load Range E or F or even G. What's the difference?

I found a discussion on Load Range in a Forum where the question was: How strong of a tire do I need? was being discussed. Here is some of the discussion:

Below you see what is stamped on my tire sidewall:
Load Range is rated at "H" 4940# single tire That's at max pressure!!
Load Range 4675 Dual tires.
Tread is 5 ply of steel. Good puncture protection with 5 steel treads.
Sidewall is 1 ply of steel. Maybe this is why they ride smoother with only 1 steel side wall.
Am I missing something since your Load Rating info does is not the same as mine. There's not enough plies to be rated an "H" tire???

Well, I felt that a better understanding of the "strength" of the Steel ply, in the subject tires, might help people understand the concept of different tire constructions 

The number of 'Ply" or layers of cord (textile or steel) are not in themselves any proof of strength. Individual cords of steel are made up of many strands. The steel or other material used to make the strands can have a wide range of strength. Also the number of strands and even the "twist" of the strands can affect the strength and flexibility in the end product. Here are some basic examples of steel cord/cable.

Each has a different configuration. Without more information it would be impossible to know which is "stronger". Don't forget tires have to flex and bend millions of times so just max strength may not be the best choice as you need flexibility too.

If we get to more complex cords we "twist" cords together and can get different properties. As seen here.

So an obvious question is how is the material selected by the tire engineer? 

There are a number of different tests conducted on tires to establish their "strength" rating and the different materials can help a tire meet the different tests. It is completely possible for a given tire to pass some tests associated with a given level. Lets say "G". BUT if a given tire only passes the "F" level of one test, then the tire would be rated as "F" even if it passed the "G" level in the other tests.

Now if the sales dept wanted a "G" rated tire then they would ask the engineer to change the specification so the tire could pass all the "G" level testing. This change or "improvement" may or may not result in more layers of steel. I can relate to an actual example of such a process in a tire I developed. It turned out in this case that the only change I needed to make was the wire in the "Bead" of the tire. This is the "cable" of wire that holds the tire on the wheel. It is kind of an anchor for the body ply. Here is a very basic image of tire components. The feature I want you to understand is where the "bead" is located.

As you can see the 'Ply" can be very complex and simply looking at the number but not the Load range can be misleading.

The bottom line is you need to know the Load Capacity in pounds that you need for your specific application. In the same size you may have different Load Range such as E, F, or G. Each Load Range has a different inflation level for the size tire you are considering and a different load capacity. So you need to consider much more than just the number and type of "Ply".

 

##RVT970

Can I run my LR-E at 65 psi? or is this overloading the tire?

As trailer owners start applying the new Goodyear Endurance ST tire, many are discovering that for some sizes the Endurance tire is only available in a Load Range that is higher than their OE tires. Some are concerned about what inflation to run. I have even seen some claim that running a LR-E at LR-D inflation i.e not 80 but at 65 that the "tire will be overloaded, heat up and fail".

While I understand some of the confusion I do not agree with some of the concern or replies.

Tire load capacity is a function of the tire size and inflation level as long as you stay in the same "type" tire.  By "type" I mean P type or LT type of ST type or for large RVs "truck" type.

If you stay with the same type and use the same numeric "size" then the only thing left to change is the Load Range or "Ply Rating". While I do not like using Ply Rating as it is an old and discontinued nomenclature it may help for better understanding in this post for you to think of the old term.

Important Point. "It is the air pressure that supports the load NOT the Ply Rating." This statement is supported for every tire made by every tire company in the world through the use of Load & Inflation tables. These tables show a size and then for different levels of inflation the load capacity of that tire when inflated to that level. You will never see a tire shown where a LR-D at say 65psi can support 1,500# and for the same size the same tire when having a LR-E rating shown a higher load capacity at 65 psi. Not even just 1 pound more.

So a LR-E can support the same load at 50 psi as a LR-C or the same load at 65 psi as a LR-D at 65.

You will not be overloading the LR-E if you load it to the 65 psi rating shown for thet type & size tire and inflate it to 65 psi as you would for a LR-D. Since you are not overloading the LR-E tire it is not going to overheat at 65psi with the 65 psi load so the LR-E tire is not going to "overheat" at 65 psi any more than the LR-D will "overheat" if it is loaded to the 50 psi load rating and inflated to 50 psi.

When going to a higher "Ply Rating" you can then increase the CIP which increases the tire Load Capacity which means it will actually be running cooler because of the greater "Margin". The higher inflation will also lower the Interply Shear which may lead to longer tire life.

When making the change you do need to confirm the upper inflation level for the rim. The wheel manufacturer should provide that information. As an alternative the wheel will have a max load capacity stated. Looking at the OE tire size that comes on that wheel look for the inflation that corresponded to that load and I would consider that to be the wheel inflation rating.

Much confusion on some RV forums

 Much confusion on some RV forums on de-rating tire load, Passenger tires and Michelin LTX tires

As some of you know I make an effort to follow posts on a number of different RV forums. Some forums are RV brand specific, some cater to the members of a specific "club" others cover the gamut of Class-A motorhomes to pop-up trailers and even slide-in truck campers. One thing they all have in common are posts from RV owners with questions about tires. Sometimes the questions receive correct and informative answers. BUT I am sorry to say that all to often incorrect information spreads like a virus with posts from some well meaning but uninformed RV owners .

I seem to be posting similar corrections over an over on a couple of topics so felt it better use of my time to cover a couple of points of confusion here in the hopes that if you find this helpful you can provide links to these facts when you come across confusion and incorrect information on other forums.

First off lets cover the use of PASSENGER tires on SUVs, Light Trucks, Multi-purpose vehicles and trailers.  "Passenger type" tires have a size designation that starts with the letter P such as P235/75R15 105T. There are also "Metric" size tires designed primarily for passenger car application made in other countries and sometimes imported into the USA. This tire might have a size 205/60R15 but to help you confirm that this is a standard tire intended for passenger car application you should be able to find the tire has an inflation level of 240Kpa or 35 or 36 psi.
If you apply a passenger type tire to something other than a passenger car (this means an SUV, Light Truck, Multi-purpose vehicle or trailer) you MUST de-rate the load capacity by dividing by 1.10.

Example a P235/75R15 105T would show Max of 2,028# at 35 psi on the tire sidewall. If used on a trailer etc the load capacity is really 2028/1.1 or  1,844# MAX when inflated to 35 psi cold.

The De-rating only applies to Passenger type tires even though many people are incorrectly posting that this De-rating also applies to LT tires.  I believe I have found the reason for this confusion and will cover that topic in a moment.

LIGHT TRUCK type tires have a size designation such as LT235/75R15  LR-E
Note the "LT before the numbers and the "LR" or words "Load Range" followed by letters such as "C", "D" or "E". The Load Range letters replaced "Ply Rating" numbers 6, 8 and 10 decades ago.

In Europe and other countries, they have "Commercial" tires but do not have "LT" as the first part of their size designation. Some may have LT at the end. The inflation may range upwards to the 85 psi level or 600 Kpa.

======
One recent series of posts involve converting from ST type tires to LT type of even P type tires. All to often only partially correct information is passed on so confusion gets compounded.

Here is an example
Michelin lists 42 part numbers for the line called "LTX® M/S2". This line of tires is specifically aimed for "SUV/Crossover, Light Truck application" and that's where the problems start. With "LT" as part of the design name some think these tires are just like Light Truck tires. Others have managed to read the fine print that says "* Passenger sizes used in Light Truck/SUV applications have reduced load capacity. This will differ from the maximum load branded on the tire sidewall." and incorrectly assumed that all the tires in the LXT line are LT tires so these folks start passing around information that LT tires should be de-rated.


The majority of the 42 items in the Michelin list are P type tires with a few LT type and even a few Euro-Metric passenger type tires mixed in. The listing even includes two "Xl or Xtra Load passenger type tires.

The LT tires have a speed symbol of "R" and all appear to be Load Range "E" or 10 ply rating for those that prefer to use the out of  date nomenclature.


"LTX MS2" is a design name much as the Bridgestone Dueler H/T 684 or Goodyear Wranger SA and I would never accuse Michelin of intentionally misleading people into thinking of this line of tires to be LT tires but the reality is that even when I engage some individuals about the incorrect and confusing information they are posting I get responses such as "I think my tires are Michelin LTX M/S2 P235/75R15 Load Range D (2150lbs)"  Here we clearly have a passenger tire but the writer has applied Light Truck "Load Range D" and the load capacity of 2,150 is for a Light Truck tire in Dual application at 65 psi. I have to wonder what inflation he is actually running.


The confusion is not limited to Michelin LXT. Earlier today I had a poster tell me that he checked the load capacity of a Mastercraft HSX which is a European passenger tire with American "XL" designation (don't ask, I have no idea how that is legal. Probably just a confused Customer Service rep I talked with)
and a Michelin Primacy of "the same size" and he claimed the load capacity was different. I pointed out that the Primacy is a Standard Load (35 psi rated) passenger tire so it would of course have a lower rating that an Xtra Load tire at 50 psi.

======================

Much of this confusion can be avoided if people would simply take the minute or so to read the tire size information on their tires and write it down.




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RV Travel Webinar Q&A Part 1

I enjoyed this first webinar on the RV Travel YouTube channel (June 28).

Hope you found the information informative.
 The answers had to be short or I am afraid I would have put some to sleep. I do want to provide as
much info as possible so I am reviewing the comments and will provide a bit more information based on the comments






Buddy Light said "I like RV tires with more plies".
    Well Buddy you may not realize but "Ply Rating" is an old term that is based on an "equivalent strength" and not on the actual number of Ply or layers of reinforcement. You can read the material list of what is actually in your tires as it is molded on the tire sidewalls. It may say something like "Sidewall 2 Ply Polyester, Tread 2 ply Polyester + 2 ply Steel".  If you have a large RV with 22.5 wheel diameter you may be surprised to learn the sidewall of many of these tires has only one Ply of Steel in the sidewall with an additional 3 or 4 Ply of Steel in the Tread area. These tires may have a "Ply Rating" of 12 or 14 but in reality there is only 1 ply in the tire.

Astrid Bierworth said "if a truck tire is the same size as the trailer tire, could we get better service from a truck tire?"
    When I heard and answered the question I was not thinking about "Light Truck" tires as when someone says "Truck Tires" to me I immediately think of Heavy Truck tires that have wheels of 19.5" or larger. Reading your question now I think you meant to ask about using Light Truck or LT type
tires on a trailer and replace the ST or Special Trailer tires that came on the trailer originally. On my blog I started a multi-part post 6/23 "Can I change from ST to LT tires on my Trailer or 5ver?" that
addresses your question specifically. The second part will be published next week. If you subscribe to my blog you will get a notice when a new post goes up.

David Lee asked a similar question. "What's the advantage/disadvantage of using light truck tires over trailer tires?"
     Sorry David our set-up didn't allow me to see the comments live. I hope you find the answer you were looking for in my series on this topic.

AaronzDad "Roger are there any tire treatments that will add back the oils and chemicals tires need to stay flexible and extend the life of the tire?"
     No the treatments mostly remain on the surface much like Sun Tan Lotion does when you spread it on your arm. They may give the tire a "New Shine" look and may provide a little UV or Ozone protection but too often many of the treatments and their application can end up doing more damage than good. Sometimes there is "Petroleum Distillate" in the treatment and this can actually attack the tire rubber. Other times the application of the treatment removes the chemicals originally put in the
tire for protection. I suggest you limit your tire "treatment" to the same wash, sponge and soap you use on the painted surfaces of your RV or car.

Lori Singels said "The highly recommended TPMS system I bought constantly leaked. They're now a paperweight on my desk."
      I don't know who gave you the recommendation but if you bought your TPMS from a reputable dealer there should have been a warranty available that would have addressed your problem. I did a post on "What is the BEST TPMS" and in it I tried to provide the features I felt were the most important to look for in a system. Remember that just having a big advertising budget so your product name is most recognized does not mean your product is the best on the market. After some research, I bought my TPMS from TireTraker and have run them on my coach since 2012 and am very pleased.

Will you increase load capacity with higher Load Range?

The question of load capacity and Load Range gets asked a lot, so it seems to be a bit of a stumbling block for a number of RV owners. Here is an example:
"I need to replace the ST235/75R15 tires on my trailer. Currently have load range C tires which is sufficient for the maximum trailer weight when inflated to 50psi but allows almost no safety margin. I want to change to either load range D or E tires. My rims are only rated for 65 psi so if I went to the load range E tires I would only be able to inflate them to 65 psi. My question is this. Is there any advantage to a load range E tire used at 65 psi vs a load range D tire at 65 psi?"

Now just because he is asking about a 15" trailer application and considering a change from LR-C to LR-D it does not mean the general answer does not apply to others, even if they are considering a change from LR-G to LR-H on a Goodyear 295/75R22.5 Class-A tire.

Let me explain.

As some of you remember, I previously covered the fact that it is the air not the tire that carries the load. For those that still have doubts, here is a picture from a special test machine that measures force and delivers the answer in color. In this case, the lowest force is Blue which increases to Green, then Yellow and finally Red at the highest force. It is clear that the tire wants to be round because of the high inflation pressure but when you press the tire against a surface it becomes flat with  the highest force in the center of the tire. If it was the sidewall that carried the load, as some want to believe, then the Red (high force) should be at the outside shoulders.

Now when you go up in Load Range you are actually looking at the capability of the tire to carry more inflation pressure. Remember to gain in load capacity you need to increase the inflation. Years ago when tires used cotton for body cord we might have 4, 6, 8 or more layers or ply of reinforcement to retain the increased air pressure. Those increments provided steps in the Load/Inflation tables. Since the late 60's and early 70's when materials improved the actual number of ply decreased and the term Load Range was applied to those steps.

So going back to the original question, when increasing the Load Range you gain the possibility of increased load carrying ability but if you don't increase the actual cold inflation, the change in Load Range will not give you any increase in load carrying capacity.

BOTTOM LINE
The answer to the question is;
 He will gain a safety margin if he increases his inflation to 65psi with LR-D but if he stays at 65psi there is nothing further gained by going to LR-E as there is no difference in the capacity at 65psi.
The same thing would apply to the 22.5 example. When we look at the Goodyear tables we see that at 110psi both the LR-G and the LR-H are rated for 6,175# single or in dual application at 100psi they both are rated as 5,675#.

Special note: It is important that you look at the table on the web site of the manufacturer of your tires as not all companies give the exact same capacity number at every inflation level, even for the same size.

Had a question about High Pressure

Most posts about tires and inflation warn about the problems of inflation being too low but I had a question about high pressure and felt it did deserve a few lines.

"High" pressure is relative.
35 psi might be high or way low, depending on the type tire just as 150psi can also be too low or too high again depending on the type tire and application. The bottom line is that each "type" tire and application has an inflation that we would consider the target. Most of the target inflation are given when the tire is "cold" which means at ambient temperature and not warmed up by running or by being in the sun.
At the extremes we might have a wheelbarrow tire or farm tractor tire which is designed to operate at relatively low inflation. Some farm tires are rated at 12 psi. Some Drag Race slicks are also designed for pressure below 24 psi.
At the other end we find aircraft tires needing 200 psi or more.

For our purposes we can limit our discussion to Passenger tires, Light Truck, Special Trailer and Truck/Bus type tires.
Passenger tires generally have recommended inflations in the range of 32 to 36 psi with some Extra Load tires rated at 41psi cold. If you read the sidewall of many passenger tires you will see a maximum inflation pressure stated on the tire. None of these inflations are the hot inflation so don't set or bleed down the inflation when the tire is hot. Many times the tire is stronger than the wheel and I have seen a few examples of wheels failing at a lower pressure than the tire when we put tires to a test of over inflation and head toward 100 psi+.

LT and ST tires have a number of different Load Ranges such as "C", "D", "E" and some even go to "LR-F"
The actual psi rating for each load range is not the same for all size tires so you must consult the Load & Inflation chart for your specific size tire. The cold inflation is also molded on the tire sidewall. In general you will see inflations range from mid 40's to 80 psi with the LR-F somewhat higher. As with Passenger tires usually the tire is stronger than the wheel but the inflations are still "cold" not hot inflations.

Truck/Bus have higher Load Range and accordingly higher inflations with some at 120 psi range.

The one constant SAFETY WARNING is to not set the cold inflation higher than the rated inflation for your specific tire and Load Range but also do not bleed down Hot tires. Tire Engineers know that tires will heat up and we test our tires at highway speed and above when the tire is fully loaded and design the tires to handle the hot inflation.

Over-inflation tires make for spectacular explosions. A quick search on YouTube shows a number of   examples .
Sometimes it is the wheel that fails.

Improper inflation can kill.


In general we see that new tires are capable of handling from 200% to 700% of the cold inflation molded on the tire sidewall when we do a burst test in the lab. With that large of a range there is no single number I can provide. The other thing to remember is that internal structural damage from pot-holes and curbs and road trash as well as simple age can reduce the maximum strength capability of a tire so this compounds the problem of providing a maximum safe cold inflation other than that molded on the tire.

Bottom Line.
Do not exceed the maximum inflation identified on the tire or wheel.
All inflation specs are COLD i.e. Ambient inflations
Confirm the max load on each tire will never exceed the load capability for your "set" cold inflation per the published tables.
DO NOT bleed down hot tires
If unsure, let a professional tire service person mount and inflate your tires on the wheels.

Have you read a tire lately? Tire Marking

Have you read the information provided to you by the tire manufacturer? If you have, did you bother to record the important numbers in your log book so you only need to do this job once in the life of a tire?

There is a lot of information molded into the sidewall of your tires. Most of this is required by law. Most of this is important for you to know so you can look up the correct inflation for your tires or if buying new tires be sure to get replacements that can carry at least the same as the original tires.
Here is some information from one tire.

First the SIZE

This tire is a "Passenger" type as it starts with the letter "P" other types might be "LT" for Light Truck, or "ST" for Special Trailer. Small tires intended for passenger cars migth not have the "P" if made to European specs. Large tires like 19.5 or 22.5 rim dia have no letter and are "TBR" of Truck Bus radials and are found on Class-A RV. The "114S" is the Service Description which is a Load Index (from a published table but using the actual Max Load is better). The "S" is the Speed Rating or max operating speed. Like the Red Line on your engine. Not all tires have this description.

The DOT Serial

This has important information used in determining the tire age. Other information such as the location of the tire plant that made the tire is part of this code ( first two characters  8X in this example). If there is a recall, this code is used to identify which tires are covered by the recall. NOTE that the last portion, the 4 digit date code, 3908 in this example is only molded on one side of most tires. Every tire sold for use on the highway in the USA must have a full DOT serial including the date code molded on at least one side. This tire was made the 39th week of 2008.

The Load & Inflation information

This is the maximum load capacity for the tire when the cold inflation is set to this pressure. In this example (2601 lbs) when the inflation is set to( 44 psi max press) when the tire is at ambient temperature. NOTE for LT and TBR type tires there is a second lower load limit for dual application (tires side by side on the same axle as on the rears). If you have two axles and ST type tires I personally suggest you not exceed the "dual" tire load as you need a safety factor in your tire loading due to extreme side loading unique to tandem axle trailers.

Tire Materials

This is really just FYI and is more like truth in advertising to let you know the materials used in the sidewall and center of the tread of your tires. In this case there are two ply of Polyester in the sidewall and in the tread there are two ply of polyester + 2 ply of Steel + 1 ply of Nylon. Most TBR tires will only have 1 ply of steel in the sidewall.

Safety Warning

This is for the person mounting and inflating the tires for the first time. Do not confuse the inflation number here ( 40 psi) with the inflation number associated with the load (44 psi). This is the max inflation to seat the bead. If you have ever watched a tire being inflated it is the "Pop" or "Bang" first heard. If the tire doesn't seat by this inflation then it should be deflated, re-lubed, re-centered and re-inflated. People can die if they ignore this warning.

Bottom line
If you get new tires and they match the Size and Load & Inflation information you are good to go. If ANY of these numbers are different you need to be sure you completely understand why and that you are not getting a tire with lower load capacity.

What is Ply Rating?

 "Ply Rating" is an old term left over from the days of cotton being used for tire reinforcement . Pre World War II. Today the actual number of layers or "ply" in the sidewall and tread are molded into the sidewall of your tires. The term "Load Range" is used today to identify the maximum inflation for a tire.

The vast majority of Passenger tires and for the most part Light Truck tires have polyester body ply material and steel belts. Most Truck/Bus tires will have steel body and belts.

In the picture above we see the two bias (angled) body ply plus the two angled belt ply in the bias-belted construction from an early Goodrich tire.

 The actual number of ply has decreased over the years as technology improved and stronger cords were developed so fewer actual layers of material was needed to contain the air pressure that is needed to carry the load.
Also the switch from bias construction to radial allowed the decrease from 2, 4, 6, 8 or another even number etc body ply to 1 or 2 or 3 actual ply. This graphic is a basic representation of Bias, Bias Belted and radial constructions.

Examples of information seen on the sidewall of modern radial tires:
Passenger tire might say "Sidewall 1 ply polyester, Tread 2 ply steel + 1 ply polyester"

Light truck might say the same as passenger but some larger LT tires might have two or even three body ply so they might say "Sidewall 2 ply polyester, Tread 3 ply steel + 2 ply polyester"

Truck/Bus tires will probably say  "Sidewall 1 ply steel, Tread 4 ply steel"

Note Any reinforcement material that goes through the center of the tread is counted so the body ply material is counted in the tread material listing.

Here is an example of a heavy duty traction design truck tire with one steel body ply and 4 steel belt ply. 

To help you understand the relationship here is a simple comparison of Ply Rating and Load range

 Load Range     Ply Rating               Load Range       Ply Rating
     A                     2                             B                   4
     C                     6                             D                   8
     E                    10                            F                   12
    G                    14                            H                  16   
    J                     18

What do all those letters mean in the tire size?

A fairly consistent problem I try to provide answers about specific tire applications, is the fact that we are usually only given part of the tire information we need to provide an informed answer. I have been asked “What load can my 16” tires carry” or “I have 8 ply tires, how much load can they carry?” or “Can I replace my 235/70R16 tires and carry more load with a 245 tire?”
While I really want to help you get the information and answer you seek, I do not want to guess what tire you have as I may guess wrong and give you incorrect information.

The reality is that the numbers alone are not all the information we need. To help us do a better job of answering your questions, you can help us by giving us the needed details.

Here are some examples of how you can help us all if you provide complete size information when you ask a question.

A P235/75R15 105S is rated at 2,028 Lbs at 35 psi maximum. This would be a “Standard Load” tire, while a P235/75R15 108S XL or Extra Load is rated at 2,183 Lbs at 41 psi max.

We can break down the different parts of the complete size designation as follows. The P stands for Passenger. The 235 is the width of the tire in millimeters and the 75 is the Aspect Ratio of how tall a tire is relative to how wide. In practical terms it is how close the wheel is to the road. The “R” of course stands for Radial and if the tire were Bias as tires were before the introduction of Radials it would have a D for Diagonal. Don’t ask me why they didn’t choose the letter B. I have no idea.

We all know the 15 is the rim diameter. The 105 or 108 is the Load Index. You can consider any passenger tire to be Standard Load unless marked “XL” or “Extra Load”. The “S” in the size above is the speed or handling rating. Passenger tires are not rated for dual application. The combination of Load Index and the Speed rating make up the Service Description.

When you ask a question about a tire don't worry about what all the letters and numbers mean just look at your tire and copy all of the information and leave it up to me and other tire engineers to decipher the mumbo-jumbo. If you tell us your tire size is a P285/35ZR19 87Y we will know this ultra wide, very low aspect ratio large rim tire with a high speed rating indicates you are driving a Corvette and that those tires are not meant to be used on your RV.

Next time we can move on to other type tires that many will find on their Pick-Up, Trailer or RV.

Light Truck tires on trailer

Had a question from a reader
Tireman:
Thanks for your expertise. I am, frankly, baffled about what to do about our tire situation. In this instance, our tire that went flat definitely was not overinflated. It had been checked about two days prior and had 63 pounds. We have been running nitrogen since the tires were put on and have not lost a pound in any of them in 3 months.
When we upgraded to 80 pound, E-rated tires three years ago, I asked about the rims' ability to hold that pressure. Stupidly, I took the tire dealer's word for it.

In 2008, we started blowing Denman tires all over Montana: three of four blew, tires with about 8,000 miles on them.
On our way to Maine in May, we blew yet another tire and sought advice from the guy who owns the campground where we were headed. He is a tire dealer, and advised us to go back to the original equipment 65-pounders, which we did. Now, we have a rim problem.
An 80-pound Maxxis, which we kept as a spare, is now on the trailer. The one that went flat will be on a new rim and used as a spare until we get home. Clearly, we had lost pressure in that tire before we got to the CG; how much is the question. It was not flat or we would have noticed it when we put the chock between the wheels. That tire will undoubtedly go bye-bye when we get home.

I will research rims. It sounds like I should replace all rims with ones that are capable of handling E-rated tires if we want to go that route again. I do not think we have room to upgrade to 16-inch wheels, but I now am going to find out for sure. If it's possible, we will do that.

I am adamant about checking tire pressure, so I am confident we have not been running on over or under inflated tires. We are not overweight, and our axles are fine.

It is obvious we are doing something wrong. I'm beginning to feel like we are too stupid to own this 5er!

Hope your eyes don't glaze over reading all this...thanks for your input.

Answer
You didn't mention if you ran 65psi or 80 psi in your "80 pound" tires. I wonder if you are running metal valves, as standard rubber valves are not rated for more than 65 psi. Also the rims have a max load and max inflation rating. Did you check the rim stamping?

You also were not clear if you were running LT or Light Truck tires or had been running ST or Special Trailer tires. These two different type tires have different load ratings even if the rest of the numbers were the same. A LT235/75R16 Load Range E has a different rating than an ST235/75R16 Load Range E.

An "80 pound" Load Range E tire rated for 80psi will carry no more than a Load Range D tire will if they are both inflated to 65psi. It is the air (nitrogen) that does the work and carries the load not the tire. Just because you checked the tire two days earlier is no guaranty you didn't get a nail as you left the CG that day and drove for two days on a leaking tire. This is one of the best arguments in favor of TPMS.

With all the tire failures I have to ask what your real ( not sticker or guess) axle by axle side to side loads are when you are fully loaded going down the road. With those numbers you can consult the manufacturer’s charts.

While you are getting the TT weighed it won't hurt to get the four corner weights of your tow vehicle too.

One thing few realize, including the tire salesman, is that according to Industry Guidelines LT tires require an inflation increase or even a load reduction if you ever drive over 65mph. ST tires also have a speed restriction that needs to be considered. The only way to know if this is not needed is to consult printed literature for your brand and design tire from the tire manufacturer. I would not assume the tire salesperson knows the correct answer.

Load Range - Ply Rating - Standard Load and related markings

Had a good question from George. He said "The tires on my Chevy Silverado say "Standard Load" rather than Load Range. What does Standard Load actually mean?"

The simple answer is that your tires are rated equivalent to Load Range B. But I am sure that raises more questions.

This is a good time to clarify some of these terms. To do that we need a bit of a history lesson so we understand why the term "Ply Rating" is out of date.

80 years ago when tires had cotton for the body fabric four Bias plies were needed for use on passenger cars. Trucks needed more air to carry their heavy load which meant more layers or plies were needed to hold the increased air pressure, so truck tires had 6, 8, 10, or more actual layers of cotton body fabric. They needed the even number because they were Bias not Radial construction.

With the invention of synthetic materials such as Nylon, Rayon, Polyester fewer layers or "Plies" of fabric were needed to hold the same air pressure. The term "Ply Rating" came into use when the actual number of plies of these synthetic materials was less than the number of cotton plies.

I remember when I started working in truck tire design in 1969 using terms like "6 for 8" meaning we were using 6 plies of Nylon to deliver the strength of 8 plies.

With the introduction of Radial construction from Europe a new size standard based on actual tire dimensions was used but something was needed to address load so about this time the use of "Ply rating" was replaced with "Load Range" and a letter was used instead of a number as the number was misleading the consumer. We ended up with Load Range, or "LR" B replacing the number 4 and C replacing 6, D replace 8 etc. Since essentially all passenger cars came with Load range B tires it was decided this was the "Standard" load and this did not need to be marked on the tire. There are a few "Extra Load" passenger type tires which you could consider like a LR-C and they are marked as such.

All Light Truck and Heavy Truck tires are marked "Load Range x" with the x being the Load Range for that tire. They may also simply have the Load Range letter right after the size.

To further confuse things there is now a "Service Description" which includes the speed rating. So you may have a passenger tire marked:
P205/75R15 84H The 84 is the "Load Index" and the H is the Speed Symbol.

A Light Truck tire might be LT205/75R15 98/95Q LRC with 98 being the single Load Index and 98 the Dual Load Index and Q the Speed Symbol and LRC indicating the tire is rated a Load Range C tire.

A heavy truck or bus tire might say 255/70R22.5 LR-G 138/134M At this point I trust you can figure out what the letters and numbers mean. If not and want more info check out
this link or simply ask the question.

Tire Loads & Inflations – A Heavy Topic – Part 1

OK so maybe the title is a bit too cute but it was suggested I try and balance my focus on highly technical stuff with a little bit of lighter stuff. Well air is light, isn’t it? Today’s key points: Know the minimum tire inflation based on manufacturer estimates. Check your inflation with a good gauge at least monthly and every morning before travel.

Tire inflation seems to be a topic that confuses some and has others believing in misleading or just plain incorrect information. Tire inflation is one item that directly affects the safety of your RV, truck or car as you travel down the highway. Many of my previous posts have been background information that you really don’t have to know or fully understand. The intent of these topics is to give you a better foundation of understanding more about tires but, if you only pay attention to one series of posts this is it.

Tires do not carry the load. They are just a container of air. It is the inflation air that does the work. Think for a moment of an impact wrench. It can’t do the work of loosening or tightening nuts on your wheels without the air, and a tire can’t do the work of carrying the load or provide the traction needed to turn, start or stop if it doesn’t have air. The load a tire can carry is based on the air volume of the tire and pressure of that air inside the tire.

If you want to get a feel for how little load your tire can carry without air in it, you can test this yourself. Simply take an unmounted tire and stand on the beads of the tire. I think you will find that the tire can support less than 5% of the rated load before it deflects more than an inch or two. Some people believe that tires with higher load range can carry more load at the same inflation. This is just not correct. You would be hard pressed to measure the uninflated load capability difference between a load range D and E tire or between a G or H load range tire.

Sidewall stamping information HERE.

If you are not sure, the "Load Range" is marked on the sidewall of your tires. If you don't see the words "load range" look for "LR" followed by a letter usually between C and G. "Load Range" may not be in large letters but you should be able to find them on your tires.
 

The simple answer to how much air you need is on your data sheet. Depending on the year your RV was made, this information is on a sticker on the side of your trailer or near the driver’s seat in your Class-A or glued to the wall inside a cabinet or on the inside of your entry door. Where ever it is, you should also have the information in the stack of owners manuals you received when you bought the new RV. Find this data sheet and write down the information for loads, minimum inflation, tire size and load range and place this info where you can easily find it. This inflation is the minimum based on what the RV manufacturer thought you would load into your vehicle. They may have guessed correctly or you may have gone way over that estimate depending on how much “stuff” you carry.

Our next blog will cover how to know the real load on your tires and what you need to do to be sure you are nor overloading your tires, wheels, axle or RV.