Your Ad here
Be sure to sign up for the weekly RV Travel Newsletter, published continuously every Saturday since 2001. NOTE By subscribing to RVTravel you will get info on the newest post on RV Tire Safety too
. Click here.
Huge RV parts & accessories store!
You have never seen so many RV parts and accessories in one place! And, Wow! Check out those low prices! Click to shop or browse!

Friday, March 25, 2022

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

 Had a question:

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

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

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


 My reply:

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

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

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

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

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



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

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

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

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


Friday, March 18, 2022

Another post on Cold inflation. Is there just TMI?

A few times each week there are posts on various RV forums asking about tire inflation. There continues to be many  readers confused by the words "Max Cold Inflation" on the sidewall of many tires. This wording, while confusing, is mandated by regulation from DOT so don't blame the tire companies. You are more than welcome to write to      National Highway Traffic Safety Administration   at 1200 New Jersey Avenue, SE ,    Washington, D.C. 20590          and ask them why they require the marking say "Max xx psi" when they know that all tires warm up when in use and that many will have inflation above the stated "Max" soon after we start driving and that many people then bleed the tire pressure down to get below the stated "Max". This bleeding of hot air pressure has resulted in numerous tire failures.

As readers of my blog you know you should NEVER bleed down the pressure in hot or warm tires and the only time you might lower tire pressure is after you have been parked away from direct Sunlight and for at least two hours, and have moved to a location that is much warmer than where you were parked the day before your travels.

 Despite the information in my posts, some folks want to play the game of trying to adjust the tire pressure for the location they are traveling to. This is not the proper method of establishing your goal "set pressure" even if the expected "future" ambient is significantly different than the ambient where you are starting your travels.

 I'm not sure why this topic seems difficult to understand but maybe I'm just too close to the topic to see the confusion. I have over 25 blog posts that mention "Cold Inflation". THIS link will display a dozen of those posts if you need a review.

 I suppose one problem may be that with the introduction of TPMS many people are now getting a bit of "Information overload"  as they watch the pressure and temperature readings from each tire go up and down as they drive. This may be the TMI I spoke of in the title of this post.

I suggest you just stick to setting the pressure on the morning (before driving and generally before sunlight has hit the tires) of your travel day. Don't try and second-guess what the ambient temperature will be tomorrow and hundreds of miles away.

I have posts on how I suggest you learn what your "Set Pressure" should be. The procedure is a little different for motor vehicles (cars, trucks and motorhomes) vs trailers.

Generally trailers need to be running higher inflation and/or lower load levels than motor vehicles because of the higher level of Interply Shear that is inherent in multi-axle trailers.

For all users, I advise that the "set" pressure be at least the minimum in the load inflation tables for the measured load +10%.

For multi-axle trailers, I suggest you follow the inflation shown on the Certification sticker but you should confirm your actual axle load is no more than 85% of GAWR if you want a chance of getting better tire life.

Motorhomes should follow the Certification Sticker inflation until they have confirmed the actual loads on their tires, then consulting the load Inflation tables identify the MINIMUM tire pressure  they should ever run. I recommend you then add at least 10% to that inflation with a +15% Reserve load capacity being better.

Remember we are trying to always protect & prevent the tires from ever being in an overload or low inflation pressure condition when we are setting the temperature.

A tire with inflation higher than x psi will generate less heat than the same tire with the inflation lower than x. As you drive and your tire heats up, the pressure will rise but with the increase in pressure the amount of heat generated will decrease so the pressure will stabilize.


Friday, March 11, 2022

Can you change a flat tire?


Have you ever given this question much thought? Your answer will depend on your answer to a number of very important questions that need to be considered first.

1. Do you have a spare? A lot of RVs don’t have a one. Their only option is to call a service and hope the service company has the correct size and Load Range (D, E, G etc) tire

2. If you have a spare, is it inflated? Given the number of folk who seldom check the tires already on the ground a majority simply forget to check the spare or don’t check because it isn’t easy to do.

3. If it’s inflated, do you have enough pressure to carry the load for the position where you are going to mount it? Your car or Toad probably has the same pressure in all 4 tires but your RV may have different inflation Front vs Rear. You probably need to be sure you have the spare inflated to the max on the tire sidewall so you can bleed it down to the correct amount for the position.

4. Do you have the necessary tools? Wrench, sockets, long breaker bar, torque wrench, jack, jack stand, steel plate to support the jack, Safety warning triangles, flares, safety vest, and lighting to see what you are doing in the dark? How about waterproof tarp to sit on while doing the job? The steel plate needs to be big enough to support the jack if you didn’t park on a hard road surface.

5. If you think you have all the correct tools, have you made sure by actually unbolting a wheel?

6. Do you have the strength to loosen and retighten the nuts? Have you ever actually tried to loosen all the lug nuts? Do you know the torque specs? Do you have a torque wrench that is big enough for your RV? I have a full toolbox and air impact wrenches in my shop but I doubt I could loosen the nuts on a Class-A. Just watch the first 45 seconds of this sales video and ask yourself if this would be you? Note I am not endorsing that product. I just liked watching the guy jump on his wrench

One other thing to consider. If the nuts have been on for a few years there is a good possibility it will take much more than the OE specs to loosen. I have broken Craftsman and SK sockets on passenger lug nuts because they were put on too tight.

7. Finally do you have the strength to lift the tire & wheel to get it on the wheel studs? 22.5 tire and wheel is over 100#.

I suggest that if you think you are going to change your own tire you need to do a few things.

READ YOUR OWNERS MANUAL and be sure you understand what you are about to do. This job is definitely NOT for everyone.

1. Pick a nice day and with the RV level, wheel chocks in place and the jack stand on a hard surface, first just see if you can loosen all the lug nuts and then re-tighten to the factory specs. Don’t do just one nut or one wheel but do them all. I also suggest you just loosen and tighten one nut at a time for safety sake as we don't need to have the wheel pop off the RV when loaded. Be sure to have someone around watching just in case.

2. See if you can move the spare out of storage and to get it back into storage again.

3. Remove an outer tire and the inner dual and put it back on again as this isn't the same as doing a front single.

4. Most important be sure you clean the threads and torque the nuts to proper specs. I find that WD-40 is good on the threads and does not mess up the torque spec.  You do know the spec for the torque of the lug nuts. It may be as low as 75 Ft Lbs or over 150 Ft-Lbs depending on the vehicle.

5. Ask yourself if this is something you want to do while at the side of an Interstate In the rain, at night?

If you don’t feel up to the job you will need to plan on having a service do the job.

If you don’t have a lot of space for a spare tire mounted on a wheel you might consider having a used tire of the correct size just in case the service company doesn’t have your size. If informed most can do a tire change for you and you will save some big bucks too. You can always pack stuff inside the tire if there is no wheel.

Finally be sure to check the air on the spare every month, even on your toad. Please be safe if you decide to do this job. If you haven't changed a tire for a few years have an experienced person with you


Friday, March 4, 2022

Your tire says "Max xx psi at Max Load of yyy Pounds" Will your tire blow up if you go above xx psi?

 The simple answer is No. Your undamaged tires are not going to Blowout or Explode or Blowup if you see a pressure greater than xx psi on your TPMS or on your hand gauge.

There is a lot of confusion out there because people do not understand the reason for the confusing wording that is mandated by DOT.

There are Federal regulations on the words and information that must be molded on the tire sidewall. This wording has been around for years with some unchanged since the 1960's.

A recent poll of RV owners responding to a question on tire inflation number on the tire sidewall indicates that 18% think the inflation number molded on a tire sidewall number is the absolute highest a tire should ever have in it. Another 18% think that inflation is "the best" inflation for the tire 2% think it's the lowest pressure the tire should ever have. I am very disappointed with this level of confusion.

Here is the reality:

Each type and size tire and Load Range has a stated Maximum load it should ever be subjected to. The number is molded on the tire sidewall in both pounds and Kg. The tire industry has published tables that provide the MINIMUM inflation a given tire needs to support a stated load. The tables clearly state that the inflation number is the inflation measured before the tire is driven or warmed by direct sunlight. This is called "Cold Inflation". Not "Refrigerated" inflation and not some laboratory 68F or 70F "standard, but the inflation that would be the same as the surrounding ambient air. Some people know this as the "Temperature in the shade".

The confusion comes about because until recently vehicle owners never knew the operating temperature and pressure of their tires. However with the introduction of aftermarket TPMS as used by many RV owners, they now have those numbers presented to them.

What is missing are two things. One being training by the selling dealer as to what inflation is needed to support the stated load and second an explanation of what the words on the tire actually mean.

I am not sure if the RV salesman has ever received the training other than to tell the customer the information is in the Owner's Manual.

Hopefully when an RV owner reads "Max Load"  they understand that they should never load the tire more than that.

The confusion comes with the inclusion of the word Max as it relates to tire pressure.

IMO the wording would be much better and more logical if the tire said "Max Load yyyy pounds at xx Psi cold".

I would leave it up to the people at DOT to try and explain why they were not consistent across all types of tires with the wording on load and inflation limits, but I have no idea who to ask. as I expect them to pass the question off and say "Ask the tire manufacturer" but the manufacturer is only following the regulations established by DOT.

I have a large number of posts in my blog that mention inflation. If you have questions I can suggest you review my posts as the questions are asked a few different ways and I provide the answer with what I believe is a consistent interpretation of the intent of the requirements.