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Tuesday, December 12, 2023

Puncture repair?

 I read this question on an RV Forum:


We picked up a screw in tire tread. Does anyone know if it can be safely patched, we have a 42 ft fifth wheel and I'm worried about pressure.


May be an image of text 

The tire dealer can confirm. There are limits on Size (smaller then 1/4') Location (not in shoulder or sidewall. 

It looks like it might be OK for "Patch & Plug".

 The tire MUST be dismounted so the interior and be inspected for damage.

Tuesday, November 14, 2023

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.

Wednesday, November 8, 2023

Check out what hitting a pothole can do to a tire


Some people want to claim a tire is "defective" and present the tire for a free replacement because of a bulge in the tire sidewall.

There is no question of there being a sidewall bulge, but my job was to actually look at tires and determine if the tire actually had a defect.

We look for marks on the wheel

When we look for evidence of some mysterious "defect," we might notice marks on the wheel, as seen in #67-5, and notice the "witness mark" on the wheel left by the tire being bent over the edge of the wheel that matches up with a mark on the tire sidewall.

Some of the marks are subtle.

Some marks on the wheel and tire are not so subtle, as seen below.

Sometimes the wheel was even bent when the impact was so severe.

And sometimes the tire sidewall even "polished" the wheel.

An inspection of the inside of the tire at the location of the bulge seen in the first photo in this series reveals some broken body cords.

How does fishing relate to tires?

In my seminars and training classes I usually can find someone who fishes. I ask if it's possible to catch a 10# fish with a 5# leader line and they respond "Yes." I then ask if it is possible to break a 10# leader line trying to catch a 5# fish and they say "Yes." When asked how, they point out that you can break a 10# leader with a 5# fish if you jerk the fishing line, as the jerk is a "shock load" on the fishing line.

I then thank the person for pointing out how it is possible to "break" or "snap" the tire body cord with the "shock load" of hitting a pothole or some other road debris.

While not every pothole hit will result in a broken body cord, in almost every case of a large sidewall bulge there are broken cords present. Some are visible on the interior of the tire, as seen above.

Other times, the cord is still broken but does not result in the interior rubber being broken if the tire is dismounted before it has been driven many miles, as seen below.

What I found on my vehicle's tire

As a side note, the picture below is a different tire than the series seen above. Tire #02-30 was actually a tire removed from the left front of my personal vehicle. A sidewall bulge was discovered by chance when an oil change was being performed.

After dismounting the tire, I reverse bent the tire to place the interior under stress, which exposed the location of the broken cord. This break happened when I was driving. I can honestly say that I do not remember hitting a large pothole or piece of road trash, but the evidence is incontrovertible. I definitely hit something hard enough to break the body cords.

Close inspection can often reveal the evidence that helps the investigator learn the root cause of the tire failure.

Sunday, October 22, 2023

"Blowout" really Puncture, Runlow and Cutting impact

 This tire was presented as just a "Sudden Blowout" with a claim that the tire "must have been defective"

This is what the tire looked like when I got it.

We can see the severe damage to the tire tread area in picture #1

In the next two pictures we can see the puncture to the air chamber which allowed air to leak out.

Here we see the small nail from the inside.  
In picture #4  between the 2 arrows we see the "rutting" caused by the wheel flange digging into the lower side of the tire. This is evidence of many hundreds of miles run with significant loss of air.

In picture #5 we see the cut steel filaments. 
In the last picture we see more cut steel filaments. Note the lack of the "cup / cone" configuration normally found in steel that has failed from being cut by some external object and not from overload or stretching.

 My conclusion was that the tire was run while not properly inflated for many hundreds of miles due to the puncture and a lack of proper maintenance. 
This would lead to weakening of the tire structure. Hitting some sharp object. the weakened tire was cut and the tire suffered a fatal failure.

Sunday, October 15, 2023

Why you should not spin your tires. A forensic analysis

 I have mentioned a few times that toward the end of my career as a Tire design Engineer I became a specialist in failed tire inspection. In my RV tire seminars I have likened this work to what was shown in the TV series CSI.

I will be sharing the results of  a few of my inspections over the next few weeks and months but will start off with one of the more exciting types of tire failure. I was not involved with the tire seen in this video but it provides the evidence on why it is recommended that if your car or truck is stuck in mud or on ice you should not spin your tires. The video is just entertainment.

I believe this truck was part of some entertainment at some auto event but it shows what can happen when you exceed the speed capabilities of a tire. The wire in the tire bead that holds the tire on the wheel can fail at excessive speed.

Here are some pictures of a tire I did receive as part of my job.

This is what the tire looked like when I received it.


As you can see it looks

like the tire was "shattered".

This is very unusual as

normally tires fail from either 

a sidewall failure from being run low on air, or have a belt detachment due to long term overloading and excessive heat.

This picture shows the broken steel of the belts and does not show signs of a detachment between the belts.


When steel fails from tension the steel shows a narrowing of the filaments as easily seen in this shot of the tire bead wire. This is classical "Cup - Cone" tensile failure of steel

Here is what the bead wire looked like.

A close (microscopic) examination of the steel filaments shows the signature "Cup-Cone" shape as seen in this Electron Microscope comparison of tensile failure vs a cut filament as seen in the lower right.

This is one of the PowerPoint slides I use in my RV Tire seminars.

So the bottom line is that if you are stuck on mud or ice and your car or truck does not have "limited-Slip" differential if one tire stops and the other spins the spinning tire can easily exceed the high speed capability of the tire.

So do not "spin" your tire in an effort to get moving. I would also recommend against showing off at car shows.

Saturday, September 30, 2023

RV tire safety 101: Old news for some, but important for new RVers

 With over 600 posts here  and with almost 300 on I sometimes feel like a broken record. But when I see the same or similar questions raised almost every week on various RV Forums, I have to conclude that there are still many new owners who have not found the answers to the questions they have about RV tires.

Wednesday, September 27, 2023

Do you trust your TPMS or hand gauge?

I use Accutire Digital gauges. I have 3 and all three are accurate to +/- 0.5 psi when I test against ISO Lab-certified master gauge at 80.0 psi.
They run about $15 on Amazon.
I have done gauge checks at a couple of FMCA Conventions and find that pencil gauges, as a group, are the worst because they get dirty and the "slip stick" in many have nicks in them from rolling around in a toolbox. 14% "failed" and were off by more than 5 psi.
Analog (dial) gauges are sometimes difficult to read as the dials may only have marks every 2 to 3 psi or so. Their failure rate was about 5%.

Concerning TPMS accuracy

I tested 6 TireTraker external sensors and 6 TST internal sensors and found them to be within +/- 2.0 psi against the Accutire master gauges. I have published the data on my RV Tire Safety blog.

At my RV tire seminars, I have suggested the following system for checking and managing gauges.
1. Get a couple of Digital gauges and compare them to each other. If more than 2 psi difference at 80.0 psi then one or both are questionable. When you have two digitals that read identical psi (+/- 1.0 psi or less difference at 80.0)
2. If you have dual rear tires and need an angle head or "dual foot" like this    

to read the outer dual you can still use that stick or dial gauge on your duals and then confirm the reading of a front tire against your "Master" digital gauge to confirm the "stick" gauge is reading correctly
3. Keep one digital as your personal master but do not use it for your daily or monthly check against your TPMS.
4. If your daily "dual foot" stick gauge or dial gauge gives strange readings compare it against your personal "Master" digital gauge that you keep packed away in a padded box. It is very unlikely that both your "master" and your daily gauge will go "off" the same amount and in the same direction (higher or lower) at the same time.

Using the above system I have been able to confirm my digitals are ALWAYS accurate to +/- 1.0 psi or less difference over the last 12 years except when the battery "died" in one digital. After replacing the battery that gauge was confirmed to match the master again.


Tuesday, September 26, 2023

Proper care of tires is NOT rocket science

 Looking at some posts and questions on various RV forums, it seems that some folks think that proper care of tires is as complex as rocket science. While I will admit I can get very wrapped up when talking about tires, I do try to be reasonable, as I believe that if the instructions are too complex, detailed, or long-winded, some folks will throw up their hands and give up. I definitely do not want you to give up.

Four basic steps for proper care of tires

Here are four basic things I think every RV owner should do. These are probably the biggest “bang for the buck” actions you can take to avoid having a tire “blowout.”

  1. Find and record the information on your certification label that looks like this:It contains the VIN, tire type and size, load range, GAWR (Gross Axle Weight Rating), and inflation. This information provides the foundation of the knowledge you need, whether your RV is a 45′ Class A Diesel Pusher with three axles…… or a 10′ bumper-pull teardrop trailer.

2. Learn the actual weight of your RV. This means that you need to get on a truck scale such as this.

Don’t worry, getting your RV weighed is easy (check out YouTube videos) and only costs about $15. By “actual weight,” I am saying you need to have the RV loaded to the heaviest you ever expect it to be. This means all the clothes, water, fuel, tools, and even your bowling ball collection on board.

3. Then compare the scale weight and confirm the number is BELOW the GAWR for your RV. If not, that means you need to carry less stuff when you travel, so it’s time to put your RV on a diet.

4. Once you have confirmed your actual weight is lower than your GAWR, you can simply inflate your tires to the PSI on your certification label.

Extra information

The PSI number on the tire sidewall is just identifying the inflation the tire needs to support max load number on the tire sidewall. That is NOT the highest inflation the tire can tolerate.

So that’s it. Four steps and you are good to go. Yes, there is more you can do such as installing a TPMS, which I highly recommend, or even learning your “4-corner-weights.” But the above four steps are what I would consider the absolute minimum steps needed.

Wednesday, September 6, 2023

Inflate with Nitrogen? Why?

Saw this question on a FB page.

" Anyone researched cost etc of replacing the air in our tires with nitrogen? It's more stable and does not change pressure with temps. All my BMW's have it. I hate checking my pressures every trip.

There were over 10 pages of replies. Some good some not so much. Here is my final answer.

Lot of time and effort in this thread but I am not sure if a consensus will ever be reached.

As a tire design engineer I can say that inflating tires with Nitrogen AKA "N2" will not hurt the tire.

Is it better for the tire? Theoretically yes as N2 is less reactive than O2 but this gets sticky when you ask if the benefits are measurable or meaningful for an RV or other street vehicle in normal operation.

I do not see where any poster of this thread has identified any problems with their tire due to Oxygen reacting with the rubber in their tires.

Let me throw a "fly in the ointment" into this topic. Those advertising the use of N2 offer a claim of improved fuel economy. However I believe this claim is based on a couple of assumptions:
1. That the average driver does not check the air pressure in their tires and with O2 levels decreasing due to the O2 reacting with the rubber which effectively lowers the tire pressure over time.
2. Lower tire pressure means worse fuel economy.
I accept and agree with those 2 assumptions
BUT With the advent of TPMS many RV owners are now properly paying more attention to their tire pressure so they are not driving with their tires at lower pressure, so what is the advantage?

I believe I can even posit a disadvantage to running N2.

If we assume, that tire pressure does not change (increase) as some advocates of N2 claim, then that would suggest tires inflated with N2 will deliver worse fuel economy as the tire running at a lower pressure than tires inflated with air, will deflect more which means it will deliver worse fuel economy. This worse fuel economy would be very difficult to measure but the fact that tires with lower pressure deliver worse fuel economy is established and accepted fact.

For me, as a tire design engineer, I feel that using N2 instead of Air to inflate tires MIGHT be beneficial to long term tire life if no effort is made to ensure you are not introducing excess moisture into the tire air chamber. If you make the minimal effort to control the moisture level.That means your air compressor tank is properly maintained and drained of the excess moisture that can accumulate in the tank, or you use a "tank-less" compressor so the only moisture introduced into the tire is the moisture in the air we are breathing.

I have a post in this blog on how to get unlimited dry air for your tires for a few dollars no matter what compressor you use. Make your own air dryer using components used in auto painting and place it in your air line so all your high pressure air is relatively dry. 

In case people are wondering what I do... I have a large air compressor in my shop. I drain it every time i Use it. I also have an "air dryer" in the line to protect my air tools from rust due to moisture. I also have the "dryer" I made in the link so I see no reason to use Nitrogen in any of my tires.

Monday, August 21, 2023

What is a good tire pressure monitoring system?


“What is recommended to monitor RV tire pressure? I check my dual tires with a hammer when on the road. I also use a gauge from time to time, but I’m looking for something a little better.”

As you may know, I monitor a number of RV Forums. I recently saw the above question. So here is my answer:

I am currently running the ONLY (as far as I know) direct comparison of Tire Pressure Monitoring Systems (TPMS): a TireTraker™ external vs. TST® internal.


TPMS “reviews”

Every “review” I see on the internet is basically someone’s opinion based on the use of one system, but I do not see anyone presenting actual data showing the accuracy of either the Pressure readings or Temperature readings. Sometimes I have noticed the “review” has links to sell the units that someone has “recommended,” but I do not see any direct comparison data or test results. I’m wondering if those posting the “review” are just interested in selling products?

I have more than 40 posts covering various aspects of TPMS on my BLOG and at, if you want to do a “deep dive.” But the basic question you probably have is:

Prior report on what is the “best” TPMS?

I started my direct comparison of TPMS brands/types in March 2018 and have test data on Pressure and Temperature readings from 26°F to 98°F in actual service, along with a direct comparison of all 12 sensors for pressure accuracy measured on a custom-built test fixture.

While internal TPMS normally report hotter temperatures because the sensor is not being cooled from external air, I can report that the temperature difference runs about 20°F cooler on external sensors. Except for that difference, I would consider BOTH systems essentially identical when it comes to reporting pressure, which is more important than temperature readings.

The original poster on the Forum said he was looking for something better than the “Hammer Test”. Here are my observations on that test.

Tire pressure “Hammer Test”

While working as a Tire Design engineer (about 45 years) I was able to observe the “Hammer Test” when a dozen experienced (more than 500,000 miles driven) truck drivers were all presented with the opportunity to “Check” the pressure on two truck tires. As I recall, one tire was properly inflated to 105 psi and the other was set to 50 psi. We ran the test twice over the day and switched the tires around. Half the drivers could not consistently or correctly identify the tire with low pressure. Three of the remaining six did identify the low tire in both tests, but provided estimates from 30 to 75 psi. Only three truck drivers were able to correctly and consistently identify the 50 psi tire as being between 45 and 55 psi both times.

If you remember that any tire operated with a 20% or more significant loss of air is considered “flat,” the test results do not support the value of a Hammer Test other than the fact that if a tire has lost 75% or more of its air the “hammer” might tell you something was wrong.

What TPMS do I recommend?

With some 30,000-plus miles of use, I feel comfortable recommending either system, as the small variation in PSI reading and temperature readings are not, in my expert opinion, meaningful to the average user. I have replaced a number of batteries in the external system and expect the internals to need new batteries soon.

What is important, even if you get or already have a different system, is to be sure you test your system at least once a year, as I covered in this post.

It is also important that you program the warning levels for your RV, as the factory setting of the TPMS may or may not provide sufficient advanced warnings for you. Here is what I do.

Bottom line. I can recommend either system. I do suggest that any TPMS be purchased from someone that supports the RV community and that has a phone number and web page with info on the TPMS. There are some low-price units. But, personally, I think a TPMS with Lifetime Warranty is a good deal.

Thursday, August 17, 2023

Can you change a tire on your RV?


Can you change a tire on your RV? This is not a question of your physical ability. While that is something you need to consider, let us set that question aside for this post. Let’s imagine we are in great physical shape; or even if we can’t lift 150 pounds off the floor, we might be in a situation where there are others around who can lend a hand with the physical aspect of doing the task.

The intention of this post is to help people focus on the parts, information, and tools that might be needed to change a tire on the side of the road.

#1 Safety: You need to be sure it is possible to change the tire without putting you or others in danger. This means getting far enough off the highway that moving traffic isn’t going to be involved. There are almost an infinite variety of locations or situations, so I can only remind you to think first and review where you are. Since you have considered the proximity to moving traffic let’s move on.


Even if you are not going to change the tire yourself you should probably have a couple of wheel chocks to place in front and behind the tire on the opposite side of the one you would change. This will help stabilize the RV when it is jacked up. When I was racing and towing my Camaro in a 26′ box trailer and needed to re-pack wheel bearings, I would leave the trailer hooked up to my 1-ton dually truck AND still I used wheel chocks.

#2 Information: No, tools are not the first thing to consider as there is some minimal information I would need to know before I even reached for a wrench.

A. Do I have a spare? Yes/No? That’s pretty basic, but I bet there are some folks that assume they have a spare when in fact they do not, as many RVs are sold and delivered without a spare.

B. Is the spare mounted on a wheel and is it inflated? Have you confirmed the inflation in the last year? Wouldn’t do you much good to change out a tire if the spare is also flat. I have suggested that sometimes having a dismounted spare can save you hundreds of pounds and dollars by not forcing you to pay the service truck premium price or even having to wait days for a tire of the proper size and load range for your RV to be located and shipped in. Some folks have found they have space for a spare and save the cost and weight by having just a tire that is not mounted. There is a lot of space in the center of an unmounted tire, so having one still allows you to place some of your “stuff” in the tire. This is most likely something owners of Class A RVs might consider.

C. Service trucks can mount and inflate a tire by the side of the road, but you need to know before the service truck is called that you have a tire. Or, if you do not have a tire, Question C is exactly what size (the numbers) and what Load Range, “F”, “G”, “H”, etc., you need. Are all of your tires the same size and Load Range? Many Class A’s have different-size tires front and rear. You do not want to pay for a service truck to come out only to find they did not bring the correct size. This is some of the basic information you need to have written down and easy to find so when calling for service you can give them that information. If you are going to rely on a service truck, the other questions about tools and air will not apply. Can you reinflate the spare if it is just low?

#3 Tools: So, moving on, let’s assume you and your co-driver and passengers or friends have the physical strength to change a tire and you have a mounted and inflated spare of the appropriate size.

Some basic items I carry myself:

Lug nut socket of the correct size. Have you confirmed the “6-point” socket fits the nuts on your wheels? 6-point sockets are less likely to slip and round out your nuts as seen here. Don’t just look, but confirm the socket is not too large. A 13/16″ socket will fit over a 21mm nut, but might be so loose that the socket spins on a tight nut and now you are stuck with a nut you cannot remove. Some nuts come with chrome covers that make proper fit difficult. Ask a mechanic, if you are not sure.

Socket extension. I have a Class C with dual rear wheels. The nuts are deep into the wheel so I needed a 12″ extension (be sure the extension is long enough) to allow a proper 90° between the socket and my “breaker bar“.

The 2-foot breaker bar allows me to generate the torque needed to loosen the tight lug nuts. My wheel nut torque spec is 140 In-Lbs., so I am using the extra leverage the 25″ bar provides to make it easier to loosen the nuts.

Speaking of lug-nut torque, what is the spec for your RV? Do you have it written down in an easy-to-find location? While we are on the topic of torque: Do you have a torque wrench that can measure at least 120% of the torque you need to ensure your nuts are properly torqued? When I am tightening the nuts I use the appropriate pattern or sequence of tightening the nuts, as covered in THIS post from my blog. Maybe in your notes you should include the sequence along with the torque spec.

For my Class C, GM specified 140 Ft-Lbs. I start with all 6 nuts “snug,” which means I turn the nut till it bottoms on the wheel. Then I step up in about 1/3 of the ultimate level so I set my “clicker” torque wrench to 50 Ft-Lbs. and, after following the sequence back and forth around the wheel, I then set for the second step at 100 Ft-Lbs., and again move back and forth in the sequence. Finally, I set the wrench to 140 Ft-Lbs. and tighten all the nuts. Side note: Checking torque does not mean removing the nuts and torquing again, but rather setting the wrench to your value and applying the appropriate torque. I would suggest you check torque every 50 miles until you find there is no movement of the nut. If you see a nut still turning after 100 miles, there is something amiss and you should learn why and take appropriate action.

Jack. Also under tools is the jack you use to raise the tire off the ground. There are many options, but I prefer a “bottle jack” as this doesn’t take up much space in the RV basement. I selected an 8-ton model as my rear axle “weight” is 10,256 lbs., so my 16,000-lb. jack is adequate. You need a jack with more capacity or the safety valve in the 5-ton jack may not allow you to lift 10,256 pounds reliably. I also carry a piece of 2″x8″x8″ board to help stabilize the base of the bottle jack if I am parked on sand or soft dirt.

Regarding jacking the RV and replacing the tire/wheel assembly: READ your owner’s manual as some RVs have a specific location on the RV that if not used could result in damage to the RV.

Suggestion: Once you have reviewed your owner’s manual and have confirmed you have the spare tire and all the tools and information you need, you can decide if you need to practice changing a tire or just review with a fellow RV owner.

Sunday, August 13, 2023

Tires without traditional rubber? A tire expert’s opinion


The concept of tires made without rubber from “rubber trees” has been around for many decades. World War II and the potential of no “natural rubber” aka latex from rubber trees became a concern for the Allies. Plantations in Asia were under threat of attack and so were the plantations in West Africa. This spurred the development of “synthetic rubber” made from petroleum products.

Synthetic rubber

Firestone produced the program’s first bale of synthetic rubber on April 26, 1942, followed by Goodyear on May 18, United States Rubber Corporation (aka Uniroyal) on September 4, and Goodrich on November 27. In 1942, these four plants produced 2,241 tons of synthetic rubber. The American Chemical Society has a booklet on “The United States Synthetic Rubber Program, 1939-1945” if you want to learn more about the joint war effort.

Following the war, various tire and rubber companies expanded their work on developing “synthetic rubber” made from petroleum and many of today’s passenger and light truck tires are made with up to 100% synthetic rubber. Some of the properties used in mining, off-road, and heavy truck tires including sizes that might be used in a Class-A RV, typically require about 65 percent natural rubber and 35 percent synthetic rubber, as some properties such as cut resistances of natural rubber have not been completely matched by synthetic rubber.


Race tires from guayule desert shrub

Last year Bridgestone Americas (Bridgestone) celebrated its first-year milestone of using Firestone Firehawk race tires with sidewalls made of natural rubber derived from the guayule (pronounced why-YOU-lee) desert shrub, grown in America’s Desert Southwest.

These tires are built in Firestone’s race tire facility in Akron, Ohio. Firestone has been working on the project of using guayule latex in tires for many years and, according to this Release, it looks like there have been some breakthroughs as Firestone has been using guayule latex for the sidewall rubber on its Indianapolis tires.


Does this mean that your RV tires might soon be made of guayule latex? Well, I would not hold my breath for a few different reasons. Volume production would require hundreds if not thousands of acres of guayule to be cultivated and grown to maturity. The use in Indianapolis tires is clearly a “Demonstration Project” and low cost is not a high priority.

Will Bridgestone enter the RV tire market?

Finally, I have not heard of any interest on Bridgestone’s part to enter the RV market, especially for ST-type tires. While currently Bridgestone and Firestone’s tires are available in LT and Class A sizes, I see little reason for the company to push to expand in the RV market as long as the majority of the tires are being overloaded and/or underinflated by the users.

While I have no current knowledge of the status of the program or what the plans are to expand the evaluation beyond Indianapolis race tires, if and when Bridgestone is ready and I hear anything more about guayule latex, I will let you know with an article here.

Monday, July 3, 2023

‘What tire should I buy?’ Find out here

 “What tire should I buy?” I get this question almost every week. I have hesitated on giving an answer as there are so many variables and unknowns. However, there are a few suggestions on things to consider when shopping for tires.

  1. The Obvious:  Load capacity. Your new tires MUST have equal or greater load capacity than the OE tires provided by the RV manufacturer. This applies to all RVs from 45′ Class A to 15′ pop-ups.
  2. Not so obvious: Load Capacity margin or “Reserve Load”. I have a post on my blog specifically on “Safety Margin” and how that can be misleading. I prefer the term “Reserve Load,” or the extra load capacity above the actual truck scale load. I consider 10% to be the minimum, with 15% to 25% preferable, if possible.
  3. Load Range (aka Ply Rating) selection. As with Load Capacity, I suggest an equal or higher rating. A higher rating would allow you to run higher inflation, which delivers increased load capacity (see #1 above). But before you increase your cold inflation level, be sure your wheels are rated for the cold pressure you intend to run.
  4. Now we get to the area that requires more thought: What “Brand” tire? Many people ask me about changing the tire brand. My first response is the question: What is wrong, or what don’t you like about your current tires? Why do you want to change the brand?

The answer will help me understand their objectives or goal for making a change, as they may not have formed a clear reason in their mind. The reason is usually one of two things: price or performance.

“Price” is not easy

While “price” may seem to be easy, it really isn’t easy. In different areas of the U.S. there are some major retailers selling different brands at significantly different (lower) prices than are available in other locations. I am aware of some large dealers in the far Northwest states with brands not available in other parts of the country. So it’s difficult for me to offer a suggestion on “what brand” when the answer depends on what state you are shopping in. Don’t even start with online pricing, as those numbers can change daily.

I do suggest that people not select a tire brand simply on price, but to do a little investigation to learn who makes the brand or brands they are considering. Over the last few years, we have seen a number of brands being bought by one of the “major” brands such as Bridgestone, Goodyear, and Michelin. Some of these older brand names may have essentially disappeared, such as the Dayton brand which is now owned by Bridgestone, or BFGoodrich which is now owned by Michelin. HERE is a link to help you learn who makes which brand of tire.

Brands to consider

As a side note, I think it is reasonable to say that the tires with brand name “ABC” that is owned by the company “XYZ” can, for the most part, be considered equivalent to all the tires made by “XYZ”. Also, in general, the “Top 3” on that page listing Michelin, Bridgestone and Goodyear can be considered the “Top Tier” using the latest technologies, and are my first choice along with the brands owned by those three. I would consider the other “owner” companies to be 2nd Tier along with the brands they own. If you can’t find the brand on the list, those tire brands would be my 3rd choice when selecting a tire brand.

You may note that there are a number of tire brands not found on that list. Those tend to be “price leaders,” which many times means the low-cost option. If shopping on price, you will probably find a limited selection of sizes and Load Range, or you may find little or no warranty. These price leaders may also have a limited number of dealers or locations to get any “service” you may need.

Special consideration for trailer and 5th wheel owners with ST-type tires

There are a couple of tire companies like Maxxis not on the list in the link above. In general, the tire volume is low enough that few major companies are interested in the “niche” ST-type tire market. I would suggest you use tire warranty as a guide to which brand to select. A longer warranty would be preferable.

There is one other item for people to consider when shopping for tires to put on their trailer or 5th wheel. That is the reinforcement material in the tire under the tread. I strongly suggest you only consider tires that list “Nylon,” “Kevlar” or “Aramid” along with steel and the body cord in the tread area. You may not find this information in advertising literature. It is also possible the salesperson doesn’t know, so it is up to you to look closely at the tires you are considering to see the materials used in the tire. ALL tires are supposed to list the materials and you should find wording similar to this example.

The Nylon will help address the higher levels of Interply Shear found in tires in trailer applications.

Monday, June 26, 2023

What does "MAX Inflation" on tire sidewall mean?

 "MAX PSI" is a hot topic on various RV forums I monitor, so let's jump in. I have answered this question previously but some folks have decided they know more than the tire companies.

First, as always, you need to remember we are talking about the "cold" inflation which means when the tire is at Ambient air temperature and has not been driven or in direct sunlight for the previous two hours. If I ever talk about the warm or hot inflation that will be made obvious in that post.

Every vehicle has a Certification Label.

This one happens to be from the side of an RV trailer. The specifics of this individual label are not important as you should have captured a nice, sharp picture of the label for your RV.  Class-A has the label usually near the driver's left elbow, Class B & C and LT have the label in the driver door jam and towables (TT and 5th wheel trailers) have the label on the outside, driver side, toward the front.

The label states the Tire Size, and the recommended inflation if it is a passenger car. If it is an RV it will give the GAWR, Tire Size, Tire Load Range, and the inflation required to support the GAWR. Passenger car and LT inflation is arrived at after years of testing and evaluation of different tire designs from different manufacturers at different inflation that balance the requirements on a long list (hundreds of items) from the car company. These requirements include Force & Moment test results and fuel economy plus dozens of detailed ratings within each category for Ride, Handling, and Noise. Car inflation is a "Recommendation" from the engineers at the car company aimed at giving you the performance they designed into the car.

I have never heard of RV companies evaluating tires. They generally look for the lowest-cost tire that can provide the load capacity required by law. This usually means for towables that the tires would need to be inflated to the level required to deliver the max load capacity. A few RV companies are selecting better tires with Nylon Cap Ply but you need to pay attention.
The inflation number on a tire sidewall is the PSI needed to deliver the Max Load rating stated on the tire. Normally tire load capacity is increased with an increase in inflation and that would normally mean you would increase the inflation, BUT since the tire was selected for its max load capacity as stated on the tire sidewall, the inflation that will deliver the highest load capacity for that tire is the "MAX infl" which is NOT the highest inflation the tire can tolerate.

Yes, the wording is confusing but the wording was, not selected with the average user in mind.
Motorhomes are built on chassis built and designed by vehicle manufacturers so the tires on Motorhomes will many times have inflation on the label that is lower than the tire max because the tires were evaluated and selected by the vehicle chassis manufacturer.

Many towables are built with minimal capacity for additional "stuff" but many people load their RV with no thought to the load capacity. This is why the data shows that over half the RV on the road have one or more tire or axle in overload. This is a major contributor to tire failures and why there are so many RV trailer tire failures.

Too often on RV forums, people do not pay attention to what type of vehicle is being discussed A Passenger car (or 1/2 tom Pickup) or a Motorhome or a Trailer (5th wheel). These three completely different types of vehicles require three different guidelines and inflation information. This failure to be specific with the vehicle type is why people get confused.

Roger Marble

Check out my Blog www.RVTireSafety.Net

Have a tire question? Ask Roger on his RV Tires Forum here. It's hosted by and moderated by Roger. He'll be happy to help you.

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Thursday, March 30, 2023

What does "MAX PSI" on the sidewall mean?


I know I have answered this question in the past but maybe it was on an RV forum for a single-brand RV so not everyone has heard this. So here goes.

Many, but not all, tires have the words "Max PSI" followed by a number on the tire sidewall. I have no idea which lawyer wrote the requirement but he or she didn't understand how those words would be misinterpreted.

Too often I see people saying that the tire should never be run with a higher pressure or that this is the absolute only correct pressure for the tire, but these assumptions are incorrect.

I hope everyone reading this post understands that tire load capacity is related directly to tire inflation and if they want to increase the load capacity they will need to increase the inflation. While it is true that an increase in tire inflation is required if you want more load capacity, there is a limit. The limit is controlled by industry standards which are published and followed by all tire companies.

Each tire has a Maximum Load Capacity and to get to that capacity you need to increase the tire inflation BUT there is a limit as each tire also has a limit or maximum load capacity and increasing the inflation above the stated pressure WILL NOT increase the load capacity.

So you have a tire that says "Max Psi 65 psi" which means you will gain increased load capacity as you increase inflation from 35 to 45 to 60 and to 65 psi BUT any additional pressure above 65 psi WILL NOT RESULT in any additional increase in load capacity.

It is also important to know that tires are tested and can tolerate higher pressures due to being warmed up by running so the pressure on the tire sidewall only refers to the tire "cold" inflation so you should not bleed down the hot pressure.


Have a tire question? Ask Roger on his RV Tires Forum here. It's hosted by and moderated by Roger. He'll be happy to help you.

Read more from Roger Marble on his blog at or on


Monday, March 27, 2023

Why is there so much confusion on tire inflation ?

 Why is there so much confusion on tire inflation versus max inflation versus my recommendation of +10%?

Here’s a question posted on an RV forum: Tom said, “So, I see some who are saying to set pressure to max cold pressure recommended, and others talk about ‘minimum +10%.’ …I’m confused.”

Starting at the end

Let’s assume you know the actual load on each tire from your measurement on a scale. (Yeah, I know about assuming. But every RV owner has been told at least once to learn their actual loading.) You take the load on the heavy end of an axle as there are almost zero percent RVs with the load exactly at 50/50% side-to-side.


The load number is then found in the Load/Inflation charts for your size tire and you go up (to the right) until you find a block with at least, or more, load than what you measured on the scale. NEVER go lower than your scale reading. DO NOT average the reading from each end of the axle weight measurement. DO NOT try to calculate a pressure between the 5 psi increments. Then look up in the chart to find the PSI. That is the MINIMUM inflation you should ever run in the tires on that axle.

Add 10% to the tire inflation number

I suggest you add 10% to that inflation number to offer some “protection” in case the temperature drops. If you have added my recommended 10%, you will probably see that you do not have to add air every day the temperature drops 10 degrees.

RVs have certification labels aka tire placards that have tire size, type, load range and inflation numbers. They also have GAWR (Gross Axle Weight Rating), which is the MAXIMUM load you should ever have on that axle. The RV company is required by DOT to post on the sticker an inflation number that is sufficient to support 100% of the GAWR. The RVIA (RV Industry Association, a standards organization) sticker on the side of your RV now requires an inflation level good enough to support 110%, which is better than the DOT requirement.

Because of these load capabilities, most RV companies select the smallest (lowest cost for them) tire that can just barely meet these requirements. The result of this purchasing decision is that you will need to inflate your tires to the level needed to support the tire’s MAXIMUM load capacity – which is the number on the sidewall of the tire.

Side issue. The wording on the tire sidewall is confusing. The reality of what it means is that any given tire has a MAXIMUM load capacity and an inflation (minimum) required to support that load. What is not printed on the tire sidewall is the fact that there is no increase in inflation that will result in that tire ever being capable of supporting more load. Therefore, the “max inflation”  wording that was decided upon by some committee 50 years ago is inadequate.