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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.

So please bear with me if you already know the information I am posting today, and just consider it a refresher course.

1. How much air do you need in your RV tires? Most important, we need to protect against overloading our tires. With most RVs on the road having at least one tire or an axle in overload, this is a most basic need. For many years RVs have come with a Certification Label mandated by Federal Safety Regulations. The labels may look like these:

2. The labels have the VIN for the RV and the GAWR (Gross Axle Weight Rating), which is the Maximum you should ever have loaded on the axle. The label also has Tire Size and Load Range (aka Ply Rating), as well as the inflation needed by the tires to carry the load. On a Class A, the label is located near the driver’s left elbow. If you have a driver door in the motorhome, the labels are on the driver door jamb. If you have a trailer or 5th wheel, the labels are on the outside, driver side toward the front. While helping an RV owner a couple of weeks ago we discovered that the information on his label had been polished right off the sticker so he will need to contact his RV manufacturer to obtain new labels. I suggest that every RV owner capture a picture and keep copies in a couple of locations.

3. Inflation needs of the tire are determined by the load you place on the tires. Every RV should at least once stop at a truck stop scale and learn the actual load placed on their tires. In tests, it has been shown that essentially no one can look at or “kick” their tires and learn the correct inflation. If you want the facts, you need to get on a truck scale. Here is a video showing the BASICS. The more experienced folks will note that the trailer in this case only got the total for both axles, which is OK for learning the basics. There are other posts here that cover the advantages of “4-corner weights” but I want you to at least get the basics. Here is my latest weight sheet.

4. If you want to confirm your MINIMUM inflation required, you can just confirm your actual axle weights are lower than the GAWR numbers on your Certification label, or you can consult a Load Inflation table like this.


5. I have a number of posts on how to use the tables, but as long as your weights are lower than the Certification Label GAWR you can use the inflation numbers on that label.

6. You should check and set your inflation when tires are at Ambient temperature, i.e., temperature in the shade. This means before the tire has been driven on or in direct sunlight for the prior two hours.

7. You should have and use a tire pressure monitoring system (TPMS) to warn of air loss due to cuts or punctures. There are a number of posts here on testing and programming your TPMS and how to care for your 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.