Should I move from Load Range D to LR-E ?

 Following an RV Forum on trailers.

Originally Posted by NavyL

If the trailer came with Load Range D tires from the factory, and you replace them with Load Range E tires - I just don't see the need to run the Load Range E tires at the full 80 psi. Tire manufactures have inflation pressure v. weight charts for a reason.

My reply:

If you change from LR-D to LR-E (or from LR-C to LR-D) you will only get an increase in load capacity, or an increase in the Reserve Load, if you run higher than the Certification Sticker inflation psi. If you look at the Load & Inflation tables (they are almost all identical for ST and LT type tires) and look at your actual scale weights you can calculate your current Reserve Load and see what inflation you would need to get to a Reserve closer to 20% or 25%. Due to the unique forces ("Interply Shear") tires must tolerate on multi-axle trailers, I and other tire engineers suggest at least a 15% Reserve with 20% being better. On my personal RV I run 20 to 25% Reserve Load.

While we are talking about the certification label, I advise people to snap a picture of the label, or labels if more than one, along with a shot of the complete tire size and Load Range info on your tires PLUS the full DOT serial including the data code portion of the DOT serial. That way if the printing on the sticker fades or your tire gets cut and destroys itself you have a record so you can file a claim if you purchased "Road Hazard" warranty on your tires as I have, or need to check against a tire recall notice, you can answer the question of what size and Load Range you are currently running. Keep a picture of the Weight Slip too. Its a lot easier to have all this tire related info in one place on your phone.

##RVT1047

Tire Loads & Inflation - A refresher

 Just read another post on a FB page where more incorrect info was published....Soooo lets go over this topic again

 Today’s key points: Know the minimum tire inflation based on manufacturer estimates. At a MINIMUM Check your inflation with a good gauge at least monthly and every morning before travel. Better yet get, program and use a Tire Pressure Monitor system  TPMS to the knowledgeable.

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 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 basically based on the air volume of the tire and pressure of that air inside the tire.

If the load was carried by the tire construction we would have Tire Load and Construction tables. But we don't. We have Load and Inflation tables because, for a given type and size tire the load is just a function of air pressure. More pressure gives more load carrying capacity.

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 capacity difference between a Load Range D and E tire or between a G or H Load Range tire because almost any significant load would compress the tire to be flat.

The term Load Range replaced to old "Ply Rating back in the early 70's when tire construction materials became stronger and with the introduction of Radial construction.

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.

TireRack has a good information page on "Load Range" HERE.

The simple answer to how much air you need is on your Certification Label AKA Tire Placard that I wrote about last week. 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 on older RVs it might be glued to the wall inside a cabinet or on the inside of your entry door. Yoyr car or Pick=up has the sticker on the driver door jam. 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.

##RVT1038

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 change from LR-F to LR-G or H? (ply range change)

A motorhome owner needs to change his 245/70R19.5 LR-F  tires and asked some questions:

My questions are:

1. Will the truck "H" rated tire give a much different ride than the recommended "F", or "G" rated tire?
2. Some manufacturers claim UV protection. Does it make a difference?
3. Are there any particular brands to steer clear of for RV tires?
4. I qualify for veterans/AARP discounts. Are there other good discounts?
5. What else should I be looking for/be concerned about?

My answer:

LR-F  vs LR-G  vs LR-H

You should never go lower. If you go up the only way you will get increased load capacity is by increasing the inflation. It is unlikely that you will get a different ride if all you change in the marking on the tire sidewall for what the Load Range is. Now if you also change brands then ride can change and if you change from a ribbed design to traction design then I would expect ride and noise to change. When you check the load/inflation tables you will note that the capacities for LR-H match the capacity for the LR-G at the LR-G inflations so it is OK to run an LR-H at less than the max inflation on the side of the tire as long as you know the actual load on each tire position and NEVER run lower inflation than what is needed to support the actual measured load.

Remember it is the air pressure, not the tire construction that actually supports the load.

I have a number of posts on my RV tire blog on Inflation as well as other tire topics so you can learn quite a bit there.

RE Brand. Yes, many to choose from. One thing to consider is how many and location of dealers."Billy-Jo-Bob cheap tire emporium and bait shop" may have the best price but with only one store how are you gonna get service if you travel?

Many of the "majors" also have alternate lines at lower cost, sometimes even made at the same plant with most of the same materials. For example in Warren Co TN Bridgestone truck tire plant also makes Firestone and Dayton brands which are less expensive. Do some research to see what other brands have.

Does the country or origin make a difference? If "Made-in-Canada" or where ever is important then be sure to read the tire sidewall as the country of origin is always listed. You can also look up the actual individual plant location by reading the first 2 characters of the DOT serial and checking HERE or HERE for actual plant location.  

UV protection:  All tires have some level of protection. There is no industry standard so it's impossible to get a meaningful comparison. Some will claim "more" or "better" but more than what isn't answered. Covering your tires will do a better job of extending tire life than simply depending on advertising.

Discounts. Yes, there are a number out there. Some might even vary depending on location as some large dealers can offer better discounts simply due to their volume.

If the price is a major concern you may be able to do a rolling change over a three year period as I suggested in THIS post.

What inflation to run when changing Ply Rating or size?

Following a few different RV Forums, I see a number of people, that clearly do not follow this blog,  have questions on what inflation to run. While many of these folks are discovering that the new Goodyear Endurance line seems to come with higher Load Range or only in larger sizes they end up not knowing what to do about inflation.
In one case the person didn't even know they were buying a larger size so I do wonder sometimes how people managed to ever buy tires for their car if all they seem to know is that tires are round and black and seem to cost too much.

When you replace tires on any vehicle, you should always be sure the load capacity of the new tires is equal to or greater than the capacity of the original tires on the vehicle.

Regular readers of this blog know that load capacity depends on BOTH tire size and INFLATION level. You also know that there is a "Tire Placard" or "vehicle certification label" on or in all your vehicles that identifies the original size tire and the inflation recommended by the manufacturer. In the case of RVs the label also should tell you the GAWR which is the maximum load you should ever have on each axle confirmed by scale readings.

So back to the original question of what inflation to run ?

 .

Example 1:  There was a change in tire size but the Load Range stayed the same.
Original tires were ST205/75R15 LR-C and you mistakenly bought ST225/75R15 LR-C
 A quick check of a Load & Inflation table for ST type tires we see that the ST205  is rated to support 1,820# @ 50 psi and the ST225 can support 2,150#@50 psi. This is a nice 18% increase in load capacity.  I would suggest that in this case the owner continue to run 50 psi and enjoy better tire life.

Example 2:  There was a change in tire size AND in Load Range as can happen with the new Goodyear Endurance.
 Original tires were ST205/75R15 LR-C and you mistakenly bought ST225/75R15 LR-E
Back to the Load & Inflation table for ST type tires we see that the ST205  is rated to support 1,820# @ 50 psi and the ST225 can now support 2,830# @ 80 psi. This is a 55% increase in load capacity.  If the owner were to run the 80 psi as indicated by the tire sidewall the "ride" would probably be hard on the TT. In this case I would not follow the inflation on the tire sidewall. I would suggest that in this case the owner continue to run 50 to 55 psi and enjoy better tire life. In this example the owner expressed concern about running lower inflation than marked on the tire. Some people even incorrectly said that running less than 80 psi would somehow overheat the tire. I pointed out that I saw no problem with running less than the sidewall inflation as long as the actual load had been confirmed with actual scale readings and that there was a good margin of capacity over the actual loading.

Example 3. A Class-A owner wanted to change from a Michelin 275/80r/22.5 to a Firestone FS 591 295/75r/22.5. His reasoning was two-fold. First he was concerned about the historical reports of  delays in getting the sometimes hard to find the Michelin size and second was the significant for him, cost difference.
Both tires were LR-H . The owner did a good job of consulting the tire manufacturer's data sheets to learn the actual tire dimensions. One poster had offered a generic tire size comparison web page but the numbers the page generated were clearly different and could lead to problems.
The load capacity for the Michelin and Firestone tires is 7,160 @ 120 The owner had also confirmed the dimensions were acceptable for the application.

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.

Are you smarter than a tire dealer? Part 1

With apologies to the TV show "Are you smarter than a 5th grader"...

I sometimes wonder if RV owners are or at least need to be smarter than the average tire salesperson.

I bring this up based on a few recent observations and experiences. Let me give you some examples and then some suggestions to help you get the tires and service you want and need for your RV.

I have read a number of examples where RV owners had their tires inflated by a tire dealer only to later discover a variety of issues such as too much air, too little air, loose or missing valve caps or even loose valve cores. While I am sure that many dealerships want to provide good service, I think it important to remember that many times it is the "new kid" that gets the job of doing a pressure check and the on the job training may be done at your expense.
I would suggest that if you are going to have a dealer do tire inflation, it is in your best interest to provide the tire tech with clear instructions on the pressures you want. If you have more than a single inflation (fronts different than rears for example) maybe just an index card with a simple graphic along with the inflations you want will avoid confusion. You might even consider specifying a few psi higher than your real Cold Inflation Pressure or CIP so the next morning when you do your check with your Master Gauge you can let the pressure down which is always easier than needing to add a couple psi.
Also I suggest a quick walk around after the inflation check to be sure you have metal caps on all your valves. A light tightening twist may not be out of line to ensure you don't loose a cap on the way home.




Now the biggie Tire Buying.

 Next to going to the dentist, buying tires may be one of our least favorite activities in life. I do not expect to change your mind on this and turn the act of visiting a tire store something you look forward to, but I would like to offer some advice to make the task less stressful and possibly extend the time between visits so you have to go tire shopping less often.


Here is where some fact based knowledge can pay off in making the activity less stressful and might even end up saving you some money in the long term for I believe that a better purchasing decision will lead to lower probability of problems.

Lets start off by deciding if we are simply "replacing" out tires with more of the same or if we are "shopping" for tires that might deliver better performance, fewer problems or longer life.

Tire Replacement
If the tires you currently run have delivered satisfactory service, why would you think you need to make a change to a different size, type or brand? To me this would fall under the "It ain't broke, but I'm gonna try and fix it" approach. If your plan is to simply replace the tires you have with a newer set then you have it easy, simply shop for tires identical to what you already have.
When shopping I suggest you first go out and read the sidewall of your current tires. Note the Brand i.e. Goodyear, Michelin, Maxxis, Duro, Cooper etc. Next the type or design. This might be a name like "Marathon" or a number like "S637". Finally and maybe most important the COMPLETE tire size this includes the letters and numbers in front of and after the dimensional numbers and would also include the Service Description part, if any, that comes after the rim diameter. Service Description has two parts: Numbers for Load Index and a letter for the Speed Symbol or Speed Rating

For size something like "235-15" isn't correct and if that is what you tell the tire dealer, what you are really doing is sending the message that you really don't understand tires so an unscrupulous dealer may try and take advantage of you.
Technically an "LT235/75R15 107/110Q Load Range D"
is a different tire than an "LT235/75R15 Load Range D".


If you are not completely clear on this you might want to review THIS post that covers the differences for Passenger and Light Truck type tires.


Trailer or "ST" tires will have markings similar to LT type tires


Class-A Truck Bus Radials or TBR type and European commercial tires will also have size information similar to LT but with no letters in front and of course bigger numbers like "275/80R22.5 Load Range G". For TBR type tires the Service Description part is optional. If your current tires have a Service Description I would include that information when identifying the tires you want to the dealer.

You may find that shopping on the Interweb an exercise in confusion as I find many tires listed with incomplete or even incorrect tire information. Poorly designed web site may not be an indication of the competence of the dealership but it is not a good sign. This might be the first sign that you actually are smarter than the tire dealer.




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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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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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Soften the blow to your wallet when buying tires

Recently read a blog post about the "sticker shock" of the cost of "truck type" tires for the large RV. I would like to offer a suggestion on how to soften the financial hit. This strategy can work for all RVs be they trailers, Class-B, Class-C or Class-A size units.

It a simple plan and will only take a few minutes to lay-out. With the planning behind us we will be prepared to take advantage of any special deals or short term sales we might come across.

Now to follow this plan there are a few bits of  information you need to have:

You need to know the exact size, Load-Range and DOT serial date for your current tires.
Sorry but just thinking you have 235-16 size tires that you bought in 2009 doesn't cut the mustard.

If you are not sure how to get this information I suggest a quick refresher is in order so you might read the post on "Reading a Tire". So lets assume you have collected the details on your tires so you know exactly what you will be looking for over the next few months.

Here is how my suggestion works.
If all your tires are the same size I would suggest you plan on replacing the two oldest tires first. The new tires would go on the front positions and the others in dual position in the back.

Next year I would buy two more new tires, place them on the front and move the tires that were on the front back to one pair of duals.

Then the third year buy two more tires, place them on the front position and move the older fronts back to the rear.

The above schedule serves a few purposes:

1. It spreads out the purchase over a three year period.
2. It has you running on the newest tires on your front position.
3. With this plan you can spend months shopping for the best deal and avoids the need to accept tires that may be years old before you even buy them. Since you know you have a plan and you know that over a six to 10 month time period to do your shopping.
4. When you are done you know your oldest tires are three years old and if you plan on changing tires when they get to seven or eight years you now have a four year period to set aside some cash for when you start the cycle over again. You can continue this schedule for as long as you own your RV and never be confronted with having to buy more than two tires in any year.


Now if your fronts are different size than your rears as seen on some large Class-A units you can't do the front tire rotation but you can still limit the purchase of your rears to just two a year

With a little planning no one should have to buy more than two tires in any one year. It just takes some thought and planning.



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Can I change from ST to LT tires on my Trailer or 5ver? Part Two

In Part 1 we left off with having to do some calculation.

I will assume you have confirmed the actual individual tire loading and have moved some heavy items around to end up with a reasonable balance of loads,

I will also assume you still want to change from ST type to LT type tires which means you must increase the Load Range and or increase the tire size to get a load capacity in the LT to match or exceed the capacity of the OE ST type tires.

Now before we move on you need to realize that "LT" is a designation used here in the US and European and some Asian countries have what they call "Commercial" tires. These Commercial sizes do not start with LT or CO but will probably look like 7.00R15  or for metric sizes 205/75R16C  The "C" in this case is not the Load Range but stands for "Commercial". The Load Range will be identified as normal LR-C, LR-D etc or possibly with RL or XL for Reinforced or Extra Load. To make this post easier to read I will limit my comments to LT type tires. Just remember there are other options that may be better for those with 15" or 14" wheels that do not want to change rims.

NOTE: All of these letters and numbers are important when selecting a size so be sure you record them all when doing your research.

So on to step
#6 Dimensions. There are two key dimensions Outside Diameter or OD and Width. Now I am confident that we all understand OD but width can be a bit confusing. Depending on the wheel well contour the overall maximum width or "Section Width may be most important. Some tires may have a narrower clearance nearer the tread so they will need to do some actual measurements at a number of locations.
It may be easiest to use the dimensions for OD and Section published for your current tires and just do a confirmation with your tape measure. Remember tire "width" is not the same as tread width.

You need to be sure the tires NEVER contact any portion of the RV frame wheel well or bodywork. You should try to have equal or greater clearance with the new tires that you have on your original size.

7. The challenge
When moving from ST type to LT type you will need to move up in Load Range or up in Size or both.

Now comes the research to see what your options are
8. Knowing the target Load Capacity and the maximum OD and Section width, it's time to use the Internet to do some research. The objective is to find tires that meet your needs for the numbers and that are appropriate tread pattern. You certainly don't need Snow Tires or heavy traction tread pattern. I would suggest that the tread be identified for "All Position" or Steer for your trailer application.
You can go to web sites from large dealers such as Tire Rack, Pep Boys, WalMart, NTB, Discount Tire or similar. You might also just Google "Trailer Tire" + the name of a large city or town near your location.
Once on their web site find the various possible tires that meet your needs.

9. If you are increasing the Load Range with the associated increase in inflation you need to confirm the wheel can manage that higher inflation. The info may be marked on the back side of the wheel or you may need to contact the wheel seller or manufacturer or you may need to get different wheels if your OE seller doesn't know what the rating is for the OE wheels

10 Finally, as I have previously suggested in my post on "The Best Trailer Tire" you need to make your purchase decision not just on lowest price but need to consider the tire warranty, even if there is a Road Hazard Warranty. Also how easy will it be to get a replacement if your tire gets a sidewall cut or unrepairable puncture.

11. Last step:  After all this work we want to do a first class job. Some might want to say you can't change from ST type to LT type due to Federal Regulations. Well a friend Dave Gray has an excellent post just on this topic. He has even provided an example of what would be the appropriate label you should apply after making modifications to your RV.


I hope these two posts have helped you understand the steps, calculations, measurements and research needed to make such a change.



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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.

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.

Can I mix Load Range ?

There was a question about mixing tires of the same size & design on an axle if the Load Range is different.

First we need to all understand what is meant by "Load Range". The official definition as published in the Tire & Rim Association yearbook says "Load Range with a letter (A, B, C, etc), Standard Load, Light Load and Extra Load are used to identify a given size tire with its load and inflation limits when used in a specific type of service, as defined in the heading of TRA tables".

Basically "Load Range"identifies the max inflation for that specific size and type tire and the load capacity of the tire when set to that pressure. many think of it as Ply Rating 2, 4, 6, etc. I previously covered Load Range and Ply Rating in THIS post.

But what do you do if you have to replace one tire on an axle because of some failure like a puncture, impact or even a "Blowout" and can find a matching tire of the same size and type but of a different Load Range?

If you are replacing the failed or damaged tire with a higher Load Range you can run it as if it was of the lower Load Range.

Example 1. You have an ST225/75R15 LR-C and can only get a LR-D.  Your Placard indicates you should run 50 psi cold. Since you know you should always run all tires on any given axle at the same pressure your only option is to inflate the LR-D replacement to 50 psi. Later on you may want to increase your RV load capacity so you may want to get another LR-D and then inflate both tires to 65 psi which will increase your load capacity of the tires by over 300#
 BUT you need to confirm the wheel is rated for 2540# and 65 psi. You will need to contact the wheel manufacturer to confirm the wheel is so rated. I am not sure if i would accept what either the RV dealer or even the RV manufacturer says as they might not have all the engineering data or have other reasons to state a lower capacity.
You will also need to confirm you are not overloading the axle or springs or frame by increasing the load.

There is another reason to increase the inflation but not increase the actual load beyond the original max of 2150#. By running the tire at the higher inflation you are giving yourself a larger "Reserve Load". Some consider this like a safety margin. By running the higher inflation at the lower load you will also decrease the internal structural loads the tire has to tolerate and this should give better durability.

Example 2. Your RV placard indicates you should br running 255/70R22.5 LR-H but you can only find LR-G. In this case you are really out of luck unless you know for certain that you have less than 5205# load and not something any higher. The LR-H tire is rated to carry 5510# at 120 psi while the LR-G is only rated for 5205# at 110psi. This may not sound like much but you should not run your tires in overload as you will do structural damage to the tire which could lead to a reduction in life and even a tire failure under some conditions.

If you are running the highest Load Range for your size you may want to consider carrying a spare tire and let the road service mount your old used spare to be used to get you off the highway. This way you will not be spending hundreds of dollars for a tire you can only use for a few miles.

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.