OK As a tire design engineer and someone with RV tire
experience let's see if I can clear up some of the partially correct and
partially misunderstood information we see posted almost daily on one or more of the Internet RV forums.
##RVT1058
OK As a tire design engineer and someone with RV tire
experience let's see if I can clear up some of the partially correct and
partially misunderstood information we see posted almost daily on one or more of the Internet RV forums.
##RVT1058
I then called upon my 40 years of experience and took the time needed to
closely examine and take measurements with special tools to identify a
location that was more probably of interest. After cutting the section
at the location of interest and found the separation between the belts
that was almost all the way across. This separation allowed the tread
area to bulge out to the shape seen in the picture of the tire at the
top of this post.
For those interested these tires were not made in China as we decoded the serial and learned they were made in Mexico.
With the physical examination complete, John was able to file the three
complaints with NHTSA. Now it is important to remember that NHTSA has
budget constraints so investigations need to be prioritized. Obvious
defects that result in physical injury would receive top priority. Also a
single or small number of complaints will be of lower priority than a
large number so if the only complaints NHTSA receives on these tires are
the three from John there may not be any action. The same situation
would apply to any complaint you might file BUT it is important to
remember that if the majority of people with tire problems only post to
RV forums or grouse to others around the campfire nothing will ever
happen or result in the quality of tires improving.
Here are Links to John's information. Link 1 Link 2
A quick review of the complaint on file with NHTSA will show that the majority are
of little or no value to NHTSA as the owner didn't provide the crucial
information of a correct and complete DOT serial. Many complaints don't
even provide the tire size or even the correct tire brand. I believe
that if people spent half the time they do on RV forums but provided
complete and accurate information to NHTSA we might all end up with
better quality tires on our RVs.
BOTTOM LINE
If you have a tire problem you need to collect the facts - Size, Brand,
DOT serial and collect some good sharp pictures in case NHTSA needs
them. Then make the effort to file a complaint. Who knows, you might
just be able to grab the interest of the engineers and have an
investigation started.
##RVT1057
In response to a reader from Australia with a question on TPMS Low Pressure Warning level, I responded...
The main reason for ST type trailer tires to gain more pressure than the LT tires, is that they are forced to support more load relative to their size & inflation than LT tires are.
If you ever look at the Load & Inflation tables and find an LT and
an ST type tire of identical physical dimensions you will see that the
ST tire is “rated” to carry more load than the LT type tire is. The
basic theory behind that increased capacity is that ST tires will be
traveling slower because people should not be traveling as fast when
towing as when just driving the car or truck. When ST tires were
introduced they were limited to 65 MPH MAX in an effort to offset the
damaging effects of higher loading than seen in LT tires.
On an RV Forum I saw some posts about tire failures:
There were some posts that mentioned the RV total weight capacity or Gross Vehicle Weight Rating (GVWR). Others were mentioning the total of the Tow vehicle plus the RV Trailer or Gross Combined Weight Rating (GCWR). While others were talking about tire load capacity.
One person responded with: "You need to pay more attention to just what
acronyms are telling you. GCWR has nothing to do with tire inflation
pressures. The tow vehicle and towed vehicle are individual vehicles and
answer to their own standards and regulations.
Maybe you should ask Roger why, during his working years with tires, the
interplay sheer problem was never corrected. (Interjecting a fear
factor for attention purposes might be Roger's goal).
##RVT1054
Another post with a question on an RV Forum.
I've often wondered why the tires on my travel trailer will gain about 10-12psi on a trip, and the tires on my tow truck only gain about 4-5 psi. The tires on my trailer are Goodyear Endurance load range E, with a cold pressure rating of 80psi. (The original Chinese tire bombs were load range D with a cold pressure rating of 65psi. I had the same problem with them gaining pressure). I usually start my trips with the pressure set at 75psi instead of 80psi because I'm nervous about the tires gaining so much pressure. On a typical travel day in the summer (in Texas) the tires will usually go from 75 to about 87 or 88psi cruising down the highway at 65MPH. I have a pressure monitoring system, and I have a lot of faith in it. My trailer weighs 9950lbs according the the CAT scale.
My response:
Tire pressure will increase i.e. gain about 2% for each increase in temperature of 10F. I have covered this in detail in a few posts on my blog. Here is one post on that topic.
https://www.rvtiresafety.net/2016/01/does-tire-pressure-really-follow-gas-law.html
Since your TT tires carry a much higher load relative to the tire
size they have to work harder than your truck tires. Inflation on
trucks gives tires a 10% to 30% Reserve load while the inflation
specified for TT tries may give 0% Reserve and the sad fact is that based on actual tire loading data a MAJORITY or RV trailers actually have a negative reserve (i.e. they are overloaded).
What can confuse the issue is when you change the Load Range you can run a different pressure BUT a couple observations. When you increase the tire Load Range you only get an increase in load Capacity when you also run higher inflation.
Without knowing the scale reading for each axle and the actual tire sizes I can only give you generalizations. It is very unlikely that your 9950# is evenly split across all 4 tires and probably one or more is supporting more than 2,487#.
You should NOT get nervous about pressure gain as we tire engineers know the temperature will increase and also the pressure will increase. You can email me directly at tireman9@gmail.com and I will be happy to work directly with you to resolve your questions and concerns.
Some information that will help us.
1. Complete tire size and Load Range info for both TT and TV
2. Scale readings for all 4 axles (TV & TT)
3. Cold inflation for the TV. You said 75 for the 4 TT tires
==============================
Well I posted the above a couple weeks ago but have not heard back so either the OP has lost interest, or doesn't want to discuss the problem.
If you are reading this blog post then you probably care about your tire inflation and understand the normal pressure increase. If not my offer to help still stands, but please provide the requested information so we both don't spend time going back and forth.
"Root Cause" is the initiating condition or first cause. Someone having a temperature is not a Root Cause or Proof of an infection but is an indicator that there is probably an infection of some sort. A "Blowout" is not considered the Root Cause of a tire failure just the final condition.
OK, as you know I follow a number of RV forums. Here is one that caught my eye. Maybe some can learn this lesson before they end up in big trouble.
The post started off with "Well, I can assure that a tire can blow up for
no apparent reason. LT275/70R18 Americus Commercial date code 3518.
Truck was shaking a bit. Thought drive shaft. If any of you ever drove
a bit heavy truck (I used to drive fire trucks) that sat for a long
time and got a flat spot, well drive shaft or flat spot feeling.
Couldn't see anything wrong but decided to take my clunker over to (a local NAPA store) and let them have a look. Its about 15 miles. Missus
following. Truck was shaking even worse. Missus said she saw the left
front "flapping" (her words) and I queried why she didn't call me so I
could pull over and check. Anyway I went to the tire and checked by feeling the
inside and there was a definite bulge. So I decided to let that go
and went in to the office and BANG! rubber off the inside of the driver
side front blew off; about a foot long x 8 inch hunk. Tire still holds
air. Always kept those tires aired properly.
Bought four Cooper Discoverer A/T All-Season LT275/70R18 125S Tires.
The old Americus tires no longer had my confidence. I praised the Lord I
was able to make it over to the NAPA without a blow out on the road.
Michelin's would have been my choice but they are outside what I wanted
to spend. I checked Sams Club and the same tires were about $100 more a
piece than the Coopers."
IMO TPMS are of little value when it comes to temperature warning for tires. Same for IR guns.
In reality, tires fail for a relatively small number of Root Cause
reasons that can be discovered, but it does require detailed and
sometimes exhaustive investigation. By "Root Cause," I mean the
initiating feature or condition that eventually led to the failure. Too
often people confuse the tire's ending condition with the initiating or
"Root Cause" reason for the tire to end up in the condition they are
observing.
For the last few years of my 40-year career as a tire engineer, my
primary job duty was to investigate failed tires that had conditions
that were hard to understand or provided confusing and sometimes
contradictory evidence as to the Root Cause for their condition. With
that background, I have developed some guiding principles for the most
likely reasons for tires to fail.
These are, in no special order:
1. External Damage. These include punctures, cuts, impacts, wheel and valve failures and similar conditions.
2. Run Low Flex Failure. This is best described by the failure of
the tire sidewall due to excessive flexing. The flexing is the result of
operation when the tire is significantly under-inflated.
3. Belt & Tread Separations. This is when the belts of a radial
tire detach from the body or from each other and/or when the tread
rubber detaches from the top belt.
4. Manufacturing Defect. For the purpose of this discussion this would be when components of a tire were not manufactured to intended specification.
The "Why" for some of these are obvious, such as the External Damage category.
Others can be further traced to various contributory reasons.
Run Low Flex Failure This is a more accurate description of what some incorrectly call "Blowout".
When a tire looses significant inflation air they flex much more that
the body cord can tolerate. Excess heat is generated which can, in
extreme cases, result in the Polyester actually melting. I showed
examples of what this can look link in THIS post.
Polyester is used in most Passenger, ST type and LT type tires. Steel
body tires are used on most Class-A RVs, the steel can fatigue. I
covered "Zipper" failures and steel fatigue in THIS post.
Belt & Tread Separations occur
primarily because the rubber around the belt cords or between the belt rubber and the tread rubber isn't strong enough. Now it
can be weak for a variety of reasons. Some might be design, some might
be manufacturing and some weakening can be caused by cumulative improper service conditions.
Now let's talk about tires made by a reputable company, i.e., one that has
tire stores and dealers with physical stores and sells tires that have a
warranty of two or more years.
If this tire is subjected to
thousands of miles of lower inflation or higher loading or operation at
higher speeds or stored is full sunlight it is reasonable to expect the
strength of the belt & tread area rubber to loose a good portion of
its strength primarily due to the increased operating temperature of the
tire. If
this tire is in service on a tandem axle trailer then there is also
increased Interply Shear which can overload the belt area rubber. The
combination of the above may result in a belt or tread separation.
Another possibility is a Manufacturing Defect.
These usually occur in small
numbers as tires are built in batches so the substitution of the wrong
type of rubber may cause tires to fail. It is important to understand
that in almost all cases this type of "defect" usually shows up at early
life of the tire. It is also very important to understand that unlike some lawyers,
engineers deal in facts and logic. Simply having a tire fail is not in
it self proof of a defect but all to often that is the position that
those in the legal profession seem to jump to. That approach may result
in a nice payout to the lawyer but will not result in product
improvement as there has been no determination or identification of the
actual initiating "defect".
Finally there is the possibility of a design weakness. Now I do
not believe that anyone is intentionally designing tires to fail but
this sometimes may occur when the performance goals of the manufacturer
are
limited to meet the bare minimum for strength and durability and the
focus is primarily on low cost. There is no absolute way to identify
these tires but I do believe there are indicators when looking for tires
that are made to a higher standard of quality and durability.
I would consider a tire company reputable if it had a chain of stores
across the country. If the tires carry the name of the manufacturer and
have a multi-year warranty the longer the better then they probably have
higher durability requirements than those established by DOT.
For ST type tires I would look for tires with a Speed Symbol of "L" (75 mph) or SLOWER. Now a side point about speed. I did a POST some time focusing on speed and strongly recommend you read it. I
do not think I would recommend any tire for general use that does not
have a speed rating molded on the sidewall. Few people realize that ST tire loading is based on the assumption of 65 mph Max operation speed
I do hope this post will help some to have a better understanding of
what can contribute to tire failure and consider what you can do to
lower the chances of having such a failure.
##RVT1049
If you follow any RV forums you probably see a statement like this every few weeks. I can tell you that tires do not fail because of some RV-Magic. It comes down to actual Science.
I educated some fellow tire engineers about this “T” function when I
proved, through lab experiments that it was possible to fail two tire with
high pressure above its stated max 18 days after it was initially
inflated.
The other condition that affects and changes the “T” in the equation is
temperature. Organics experience constant change (loss) in properties as
the temperature increases. The rate of change (aging) doubles about
every 18 degrees F of increase in temperature, so it's not easy to
calculate or predict the time it will take for an organic structure to
fail unless you can control the temperature over time.
Bottom line. It’s a combination of temperature (heat) and time
that causes tires to fail. A tire that spends its life in Flagstaff,
Ariz., could probably last twice as long as a tire that spent its life in Phoenix
if all other operating conditions were identical so even knowing the state where the RV was used isn't sufficient.
As the owner of an RV you can significantly affect one factor and that
is the heat generated internal to the tire. When you run fast or
overloaded or under-inflated you are running hotter. This means you are
speeding up the rate of "aging" of your tires and can expect to see a
tire fail before it wears out. You can also protect and shield your tires from the heat generated when in direct sunlight while your RV is parked. HERE you can read about an experiment I ran on the benefits of shielding your tires from Sun exposure.
##RVT1048
Following an RV Forum on trailers.
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
I would strongly recommend every RV owner watch the four videos from Goodyear.
https://www.goodyearrvtires.com/helpful-videos.aspx
Note: If you have problems running the videos you can try using VLC Video Player. Download for free HERE
While they focus on RV applications, the information can still be informative and educational for anyone that owns a vehicle that has tires. Watching these will also give you a break from my run-on sentences in my sometimes over-detailed posts.
PS I know Tim Miller, the Goodyear Engineer in the video. While I never worked directly with Tim we did share some knowledge about tires in RV applications.
##RVT1046
Had a question:
I've read many comments on various RV forums about truck tires vs. "motorhome" tires as it pertains to cost. Some also mention the firmness of the ride as one of the comparison differences. Upon reading several tires' specifications I've seen that some have 16-plies ( for example: Michelin xza2 energy 295/80r22.5) whereas others have 18. This leaves me wondering if the number of plies can help predict ride firmness?
Does the advertised number of plies refer to the sidewall or to the portion of the tire that touches the road surface? (I'm guessing these can be different.)
Also, what other factors and/or specifications contribute to a tire's ride firmness that may help us compare them?
My reply:
When people talk about the "ply" they are usually referring to the sidewall as the number of layers under the tread is always more as there are usually two to four or more additional layers under the tread of radial tires.
I suggest you read the tire sidewall of your motorhome tires. I believe you will see that those tires say something like "Sidewall 1 Ply (or layer) of steel". The use of "ply rating" in advertising is just perpetuating the confusion that started in the 70's with "Ply rating" such as "6 for 8" or even "8 for 12" when better and stronger cords were introduced in Bias truck tires.
With the switch to radial construction, you will find that most radials from car to light truck and even heavy truck have just one "ply" or "Layer" in the sidewall. The letters for "Load Range" replaced the "ply rating" advertising because some people don't understand the concept of "rating". When you are looking at large radials with "Load Range" of F and higher all that those letters are telling you are the inflation level the tires can tolerate.
If you look at the published Load & Inflation tables you will see that some sizes are available in a number of different Load Ranges.
While these are LT tires they show both Inflation, Load Range and Load rating.
Here you can see that some sizes only come in one Load Range while others come in many. You will also note that a Load Range C, D, or E are only rated for the same number of pounds if the Inflation is the same.
One tire I designed was a Load Range E version of a Load Range D tire and after running all the required tests it was discovered that for this specific tire I only needed to change the number of strands of wire in the bead area (where the tire attaches to the wheel) to meet all the strength requirements. So you can see that it is impossible to make a broad statement on the tire construction to provide any useful information on the possible ride qualities of two different Load Range tires.
If you were to conduct a controlled ride test of 295/80r22.5 size tires with different Load Range but ran the same inflation level you would not be able to feel a difference in ride. However if you were to change the inflation level to achieve greater load capacity you might feel a difference but in that case wouldn't you expect a heavier loaded vehicle to have different "ride"?
My original question in the title of this post is intenionally misleading as you will find that the load capacity of a "10 ply rated" tire and a Load Range E tire of the same size from the same drsign are really identical.
##RVT1045
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.
##RVT1044
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
##RVT1043
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.
##RVT1042
So I came across another post on an RV forum. I am sorry to report that many of the posters did not understand the concept of Cold Inflation. The OP asked:
Why did I have three Blowouts?
##RVT1041
Tire load capacity is basically a function of volume and pressure as seen here Load = K x (Air Volume x Air Pressure) with different type tires having different “K” factor. Tires in LT applications are required to support lower load as a percent of their volume and pressure so they do not have to “work”as hard so they do not generate as much heat.
More heat means a greater increase in pressure. (Approx 2% pressure increase for each increase in temperature of 10F)
Please note that the actual load calculation is much more complicated as the response to air pressure is not linear and different aspect tires i.e. 75 series vs 85 series etc have some different factors that are applied to the actual calculation.