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Friday, July 3, 2020

Valve Stems and TPMS Part 2

As a follow up to last week's post of why I recommend people NOT use rubber valve stems with their external TPMS sensors I decided to show some of the "guts" of valve stems.

Standard "rubber snap-in" stems like the TR413. If you look down the hole you can see the end of the brass part of the stem. More on this later.

These have been used for decades on hundreds of millions of tires. These can be installed by hand using a "puller" that stretches the rubber which makes the diameter of the stem small enough to "snap into place in the wheel hole.

Once installed the wheel "pinches" the rubber part of the stem to seal the air in. The arrows show the location of the wheel relative to the metal part of the stem.  Note the part of the valve stem that goes into the air chamber was cur off before I took this picture.

You can see that the brass stops before it gets past the edge of the wheel. This makes installation easier.

Next, we have the "High Pressure" stems such as the HP-500.

 Here you can see the brass part extends almost to the bottom of the valve and into the air chamber.

When the rubber is buffed off you can see that the brass part extends through the wheel hole (location shown with the arrows.)

Now when we look at a "bolt-in" stem, like this TR416s
we see the location of the wheel hole at the arrows. We can also see the much larger brass body (nickel-plated in this piece) that goes inside the air chamber and expands to a broad base. This type of stem needs to be installed through the wheel hole with the rubber grommet sealing the air. An external washer is used and the nut is to be tightened to specification to prevent air loss.

I am also including pages from the US Tire & Rim Association yearbook which publishes the "interchange and fitment" specs so all tire companies and valve manufacturers know what dimensions are required. This is the book where all the Load & inflation tables come from and might be considered the Tire Engineer's "Bible" and is used by tire engineers around the world when they are making tires that are intended to be used in the US.

Here we find the details of valve stem designs as specified by TRA.

Finally to show the attention to detail here is the spec for the little pin that sticks out of the valve stem. Not meeting this specification could be the reason your TPMS does not register your tire pressure. (Yes I have run into that problem)

 I just wanted to try and give you a little understanding of the attention to detail tire engineers go-to when designing tires and when trying to understand the "why" for a tire to lose air.

Wednesday, June 24, 2020

Valve stems and TPM Sensors

I read the ongoing discussion on what valve stem to use with an external TPMS sensor.

A standard 65 psi max, rubber valve stem is very flexible as seen here.

 Some people think the 80 psi max, "High Pressure"

 HP 600 rubber valve stem is Ok to use with external TPMS sensors but you can see the HP-600 is still flexible.

 Here is proof that an HP rubber stem can fail when a TPM sensor is installed.

IMO staying with any "snap-in" type stem is false economy given the metal bolt-in stems only cost $3 to $4 each. Not all tire stores will have the metal valve stems so check first. if they don't you can get stems at AutoZone, O'Riley's, Advance Auto Parts or NAPA or most any auto parts store or even on Amazon.
They are easy to install too. Don't let the service center tell you installing metal stems is a lot of work.  Watch and you will see.


Friday, June 19, 2020

Another post & question of "Trailer tires vs Truck tires"

Original post and question on a 5th wheel RV forum I follow.
"Searched this forum (no, didn't search travel trailer forum) for any info on using LT (truck) tires instead of "trailer" tires on a 5th wheel.
Nope, didn't find anything - So,
Any problems with using a 6 or 10 ply LT tires on my '99' trailer instead of the replacement tires for trailers?"

He gave the dry weight and stated GVWR but no actual scale readings. He also did not provide information on his current size or type or Load Range of his tires. He did provide info heard around various campfires. In the forum, there were a number of replies. A few OK and sadly a number just plain incorrect.

In the'60's RV trailers were mostly smaller single axle and towed behind a car or 1/2 ton P/U. RV companies wanted less expensive tires. Speed limits and actual travel speeds were lower so Goodyear came up with "Special Trailer" tires with a 65 mph max speed as part of the load formula specification. This speed reduction and decreased tread depth theoretically offset the increased load capacity when compared to the same dimension LT type tires.

In 2002 after the Ford Explorer fiasco, new tougher standards for tires were implemented by DOT. RV companies fought to keep the old test requirements for ST type, the same as they were in 1968, while P-type and LT-type had to meet new, tougher standards for the 21st Century.

In 2017 China was accused of "dumping" cheap tires of all types into the US market. Trade restrictions by FTC (not tire safety standards) identified speed-rated tires as not having to pay the import duty. Almost overnight almost all ST type tires became speed rated. The SAE test for speed rating is stated as a "passenger car tire test" but was applied to ST type. It only requires tires to run for 30 minutes at the stated speed and to not come apart.

Back to the OP. "Dry weight" and GVWR are of no value when selecting tires. GAWR is almost useless as it is well documented that a majority of RVs have tires and /or axle in overload when actual loading is measured on scales.. The only weight number that really means anything is the actual scale reading for each tire, as RV weight is almost never exactly split 50/50 axle to axle or side to side. Some big RVs have been found to be 1,000# or more out of balance.

Reserve load is the extra load capacity above the actual load. Cars and P/U have reserve load in the 20% to 40% range while RVs have 0% to maybe 10%. That is a MAJOR reason for the difference in durability. There is also the shear forces seen in trailers that can be 24% higher than an identically loaded tire on a motor vehicle. This is a function of suspension dynamics. Tire Interply Shear was a complete unknown back in the 60's and not as well known or understood even in the 80's. You see the large tread distortion due to lateral loading when backing into a parking spot when the tire bends sideways. You never see this bending on a motor vehicle. The shear is always there in every curve or turns not just when backing into a parking spot. Even the normal sway observed when a trailer is towed down the highway is generating high Interply Shear. You can lower, but not eliminate the Interply Shear by increasing your Reserve Load.

So how do you improve your Reserve Load? An increase in load capacity would be a good approach. For most trailers, there are a number of options. Increased Load Range is one as long as you confirm wheel limits on load & inflation. Changing to larger tires. Even changing to larger diameter wheels might increase load capacity. I have seen some that increase all three specs, with reports of eliminating all tire failures other than road hazard or valve-related issues that can occur on any size, brand, or type tire.

If or when you replace tires the new tires should ALWAYS at a minimum have equa load capacity.

I have covered the above in numerous posts on my blog if you care to learn the facts from an actual tire design engineer.

Or you can listen to the guy in the camping space next door or the salesman at "Billy Jo Bob's Cheap Tire and Bait Emporium".


Sunday, June 14, 2020

New updated post with videos on how tires are made.

The original was posted July 2019 but there are new and better videos available so I updated all the links.

Friday, June 12, 2020

Tire "Flat Spotting" when parked

Another post from an RV forum
"I'm no tire engineer but I always thought of a "flat spot" as an area ground off from a long skid. The old bias ply tires of years ago would "deform" or become "out of round" (especially in cold weather) but a few miles of rotation would flex it back into shape. But that's all just semantics."

Well I am a Tire Engineer and the correct terms are "Flat Spot" for an out of round condition. and "Brake Flat Spot" for having an area of the tread worn off due to locking up the brakes so the tire is dragged along the road and does not rotate. When I was racing I would sometimes lock-up the brakes to avoid a spinning car. This would give a strong vibration and we would have to change the tire at the next pit stop.

You can develop "Flat Spot" from long term parking. The degree or level or amount of this type of flat spotting depends on time, temperature load, inflation pressure, rubber chemistry and tire construction.
You can decrease this flat spotting with:
Lower Load  or Higher inflation or not parking when the tire is still hot or keeping the tire out of direct sunlight
The owner has no control over the rubber chemistry or tire construction.

FYI In general tires with Nylon cap ply (seen in tires with higher speed rating) tend to develop and hold the flat spot longer, but I would not reject tire purchase because of the Nylon cap ply as that might give you more life of the tire.

You can see and probably measure the amount of flat spotting from either brake lock or long term parking if you check with a "Free Spin" inspection as seen in the video in THIS blog post. 


Friday, June 5, 2020

Tire Advertising claims ???

Read this on an RV forum.

"I am using Carlisle Radial Trail HD Trailer Tire, not at all but I think it is a good tire for my trailer. these tires have an added protection against the heat with built-in weathering and ozone protection. And with the summer months getting into their absolute hottest parts, this feature could be a nice addition to have in my trailer tires. Additionally, these tires have interconnected tread blocks that I find encouraging. See, this interconnected tread blocks ensure the tread will last for a longer time and that’s something I find it very intriguing."

I have nothing against Carlisle.  I do find the ability of Copywriters to make features common to almost all tires sound unique and special. I do question the ability of anti-ozone waxes and oils to provide any "protection against heat" and I consider that claim a serious stretch. I would love to see any test data that supported that claim.

Be a smart shopper and don't fall for slick promotional claims. Ask to see the data and results from direct comparison tests. You will many times just get the sound of crickets.

Friday, May 29, 2020

Are your "Nuts" tight enough? Part 2

This topic of how to ensure your Lug Nuts are tight enough, but no too tight,  is a two-parter and this is Part 2.

The first part, if you missed it, covered the Science and Engineering behind the basics as I am expecting that there will be a number of people who will say something along the lines of "Roger, You are all wet. I've done it THIS way for years and never had a problem".

You are certainly welcome to ignore my advice and continue with the methods you have used for years. My target audience is those who are still new to the RV life and do not have years of automotive or mechanical background or training, and those that want to ensure they do not end up with a wheel coming off their RV or breaking a wheel stud.

OK let's jump in.

I am confident that no one wants a wheel of their car, RV, trailer, or dolly to come off while traveling down the road as seen in THIS video. Or maybe even worst to cause someone personal injury as seen HERE. (The man suffered a fractured skull and chest injuries). So what do we all need to do to prevent a wheel coming off one of our vehicles? It's easy. Just make sure all your lugs nuts are properly tightened and neither the wheel or nuts or studs have been previously damaged. Sounds simple enough but how do we do that?

First, you need to know how tight the nuts are supposed to be. This information should be in your Owner's Manual 

You can check out this YouTube How to Tighten "Nuts" - The Right Way. Note: I covered the sequence for setting or checking the torque depending on how many lugs you have on your vehicle in THIS blog post. One important point to consider. If you had service on your brakes or tires and someone else tightened the lug nuts how do you know they did the job correctly? Many of us have heard about or experienced an over tight lug nut so I recommend you set the torque your self as seen in the video. Then when you are doing the recommended "Torque Check" at 50, 100, and 150 miles you will know that you don't have a nut that is significantly over tight. Note if your owner's manual has different mileage for torque check follow your owner manual. If you find a nut that turns after the 2nd check keep an eye on it in the 3rd check and if still turning you need service as something is wrong.

Let's review the tools you will need and seen in the video.
Remember this info is aimed at owners of RVs with tires smaller than 19.5"So if you are in a Class-A you can read to understand what is happening to your "baby" when you call the service truck.

Torque wrench, 6 point socket of the correct size for your nuts, 2' "Breaker bar", 12" long 1/2" drive extension to allow you to get to your dual wheel nuts. Note Trailer owners may not need this tool.
You will probably not need to use these tools too often so top quality (expensive) is not needed so in those cases I head for Harbor Freight for low-cost tools.
Check these links:
1/2" Drive Torque Wrench. Harbor Freight    or  Lowes

1/2" drive extension     Harbor Freight   or Lowes

6 point "Impact" rated socket I recommend you not use a "12 point" socket as they are more likely to spin off or round off your nuts. You do not need to buy a set. You might want to confirm the size by borrowing a socked from a friend or fellow RV owner. Example 13/16"  Lowes
Note it might be better to go to Lowes or similar as you do not need a set, but be sure to get the correct size not something close enough or you can damage the lug nuts. Here is a 3/4" socket from Lowes.

Now how do you get the tight nut off? a 2' long Breaker Bar will make the job easier. This is what I use. and I can easily generate 200 Ft-Lb

OK so with all the tools you may need collected, How do you set your clicker torque wrench to the spec for your vehicle,
Here is a YouTube to help those who have never used a Torque Wrench.

Hope this helps and if these couple of posts help a few RV owners avoid problems we will be happy.


Friday, May 22, 2020

Lug nut Torque? Why is it important and why measure the force? Part 1

Here are some YouTube videos on the topic of Torque". What it is and how do we measure the force. As an engineer, I sometimes just assume that everyone understands some basic Engineering terms but I am wrong to make that assumption. You don't have to remember all the details. I am just hoping that when we are done with this topic you will accept our recommendations on how to set and how to check the torque of your lug nuts.

Important info. It is impossible for me to know the size lug nut or specification for every vehicle but you, the owner should know this important spec and it should be in your owner's manual. If you can't find it, find a dealer of your brand RV or check the on-line forums for other owners of your exact make and model and ask what the specs are. These numbers are critical for the safe operation of your vehicle. I can only talk in generalities in this blog.

One thing to remember is that for Class-C and Class-B RV motorhomes and for RV trailers as with your car or pick-up with 14" to 16" steel wheels, the torque spec is probably between 75 Ft-Lb and 85 Ft-Lb, while 19.5 tires run about 135-145  and 22.5 tires run 450-500 Ft-Lbs. So you folks with large wheels will have to depend on the service truck to tighten your lug nuts. It is possible to get a hand torque wrench with 1/2" drive sockets that will get you to the 150# to 200# range, but it is probably safer for you to leave the larger wheels and lug nuts for the service tech that has the proper tools. I will address the tools you need next week.

Here is a video that explains what torque is?

Friction is the next topic.

For proper torque of our lug nuts, the stud and nut need to be clean, rust-free, no damaged threads, and no oil lubrication unless specifically specified in your owner's manual. If you have had problems with a stud or nut, such as a nut coming off, or broken stud, or the wheel being partially loose or the threads have been cross threaded or the nut was significantly over-tightened, both the stud and nut should be replaced. Over-tightening can get the stud into the "yield" load range which can lead to incorrect tightening and even to stud failure.

This video shows why nuts come apart
"Transverse vibration" is what happens with a wheel is fastened to a hub. This is why we need to check torque to be sure the assembly is retaining it's clamping load after we start driving.

Tensile strength is covered in THIS video.

HERE we learn about SHEAR

Ok, enough "Engineer speak". This stuff is what we engineers learn and use when designing joint and developing specifications for studs and lug nuts. There is no test in my blog on this topic, but if you are going to argue with an engineer, then you will need a solid understanding of these forces.

Now the next step is for you to do a little research
A. Find your owner's manual and look up the specifications for each of your vehicles.
B. Make a note of the torque spec and lug nut size where it is easy to find. A permanent marker on your door jam might be a convenient location.

Ok here is a short video on using s "Clicker" type torque wrench.
We will cover this tool and some others next week.

Stay Safe

You can check out this "entertaining" YouTube from a guy in Australia on How to Tighten "Nuts" - The Right Way

Friday, May 15, 2020

Was your "Blowout" caused by parking at Quartzsite two years ago?

This is a bit of a continuation on the topic of "tire Dressing" from last week's post.
I do wonder how many that complain of sidewall cracking or less than desirable tire durability makes the effort to protect their tires from the heat and UV degradation from direct sun exposure.
While there might be some benefit and shielding from applying such as "Dressing" or "Shine" or other "stuff" to the tire sidewall for UV shielding. No dressing will protect a tire from the accelerated aging process due to being "baked" by the sun's heat.

There is no standard SPF for tire dressings as there is for sun-tan lotion, It would not be that difficult to measure the level of UV shielding by measuring the UV going through some clear plastic sheeting and then applying the tire dressing to the sheeting and measuring the level of reduction if any in UV rays.

In many cases, the rubbing of the tire sidewall when applying a dressing can remove the special anti-oxidants and UV protection provided by the chemicals the tire companies use in all tires.
All rubber, natural or synthetic, loses strength and gets stiff over time. The rate of degradation is also temperature-dependent with the rate effectively doubling with each increase of 18° F. As I have shown in my blog on the use of tire covers sunlight can easily accelerate the rubber degradation by 4 times with 8 times not unreasonable in Southern states. This loss of strength and flexibility can eventually lead to a belt separation, which many sometimes call a "blowout". Maybe that unexplained "blowout" in June was brought about by the eight months of direct sun exposure in Quartzsite, AZ, over the last two winters.

I have confirmed, with temperature measurements, the significant temperature drop with the use of white vinyl covers on Class-B, Class-C and RV Trailer sizes, and the use of a flat mesh "Tire Shades" on Class-A motorhomes. I would recommend against the use of black or dark color solid vinyl covers as they would act more like an oven by both transferring the sun's heat to the tire and preventing cooling air circulation around the tire.


Friday, May 8, 2020

Tire "Dressing" and "do not use covers"! Where's the test data?

Been following a long thread on an RV Forum on the topic of "Tire Dressing" aka tire treatment or "Tire Shine".
The good news is that most posters knew to not use any product that contains Petroleum Distillate. Too bad some RV dealers don't follow the guidelines on this. I have seen a number of display coaches almost dripping with some slippery fluid. Might be Brake Fluid or even motor oil as the tires were shiny and I could scrape the coating off, leaving a "slimy" substance on my finger.

I saw a number of different products mentioned and many suggestions that a product called 303 was a good UV protectant.

I saw no one provide any actual direct comparison test data for any product that would support the claim of protection against UV damage. With a little work getting through the maze of retailers selling "303" I finally made contact with their customer service. I asked "Can you provide any test data on 303 vs other tire protection products. Also info on if 303 application removes any of the wax or oil or anti-ozone chemicals built into tires." The answer was that they would ask their chemists. This seems strange that a company making claims on the performance of their product would not have comparison data available that would back up and support the claim. Please note, I am not saying that 303 does not offer some "protection" against UV damage to tires. I am concerned that the actual application as seen on YouTube may be removing the special waxes and anti-ozinate chemicals tire companies put in our tires.

If I receive actual test data that compares 303 against other products that make similar claims I will post on this blog.

What was most concerning were a couple of posts where the writers claimed
"I got tired of reading all the opinions on tire dressing so went to the source, Michelin. They stated that washing tires with mild soap is the only thing they support on their tires, no dressing no covers, no nothing. You don't see shiny tires at a truck stop and these are the people who put on the miles."
Another said "Goodyear RV tire guide says. Just keep them clean, no dressings, no covers, zip. You can use the same stuff you wash your RV with perhaps use a medium brush on stubborn spots."

I responded:   Interesting comment on "no covers". Wonder what Goodyear RV guide you are looking at? 
I found in THIS Goodyear RV Tire Guide and under storage the advice to store tires "in sunless area" and "Don't store tires where they are subjected to direct sunlight or extreme temperatures".
Based on the above, how does telling us to not use tire covers make sense?
I have confirmed with actual test data that covering tires can reduce the tire temperature by about 40° F which could extent tire life by many months, depending on how long you protect them from artificial heat aging.

I checked and found just the opposite on the shielding from the Sun. In fact I even contacted an Engineer at Michelin and he said "Our position regarding tire dressing and protection has not changed. It is still recommended that tires are cleaned with a mild detergent and water, and they are protected from direct sunlight when the vehicle is parked for extended periods of time. This is usually accomplished with the use of some type of cover. "

So I don't know where the "no cover" info from either Goodyear or Michelin comes from and if you read my blog you know that this tire design engineer is a strong proponent of using White vinyl on Class-B & C tires and the flat mesh of any color on Class-A.

I have nothing against 303. I am wondering why, for the price they don't have any actual direct comparison performance data on UV protection.

PS. If you don't want to protect your tires from the heat aging due to sun exposure please don't ask me to explain why you don't get longer life from your tires. Also next time you run into someone selling an brand  "Tire Dressing" ask to see the test data and see what happens.

Friday, May 1, 2020

Is Moisture in tires a bad thing. Why with RVs?

The question of Nitrogen being used to inflate a tire has been covered in a few of my blog posts and on some other posts on the internet. It is often mentioned that the Nitrogen used to inflate tires is "dry" and so that is considered a positive but I don't recall anyone getting too specific on why "dry" is better than "wet". Before we get into that part of the discussion I want to be sure that everyone understands that any "gas" you buy in a high-pressure tank aka cylinder, will be "dry" as the process of separating the gas and compressing it removes the moisture. So if you were to buy a cylinder of CO2 or Argon or Helium etc the gas would be "dry.
I did a post in May 2012 as one of my early posts on How to get dry air for your tires by making your own air "dryer" for less than $20 for an almost endless supply any time you need it.
There are some companies that sell small cylinders of various gasses but you would also need to have a pressure regulator and a source of high pressure (1,000 to 2,000 psi) gas to refill your tank.

But back to the original question of why do we want to keep moisture out of our tires and why would getting "dry" or at least "dryer" air for our RV tires be advisable. By "Dryer" I am referring to the wet air you can get out of the "free" air at some gas stations where they might not maintain their air compressor or air dryer.

In the past when RV trailers came on Bias or tube-type tires we didn't worry too much about dry air primarily because the tube did a pretty good job of keeping high-pressure moisture out of the tire carcass plus those bias tires did not have steel belts and were probably just Nylon or Rayon cord.

The modern radials we use today are almost all "Steel Belted Radials". So the question is what happens when you "mix" steel and water?  The steel can rust over time. Now in most tires on your car or TV you may drive it almost every day. The driving generates heat and this heat is highest at the belt edge which would be the most susceptible to moisture. This heat tends to drive the moisture out of the tire rubber. However, if you let the tire sit for days or weeks moisture in the air can migrate into the tire structure. Moist inflation air can be driven into the tire structure and over time this moisture can attack the ends of the steel belts and form iron oxide. Rubber doesn't stick very well to the rusty steel so tears can initiate at the molecular level. Once cracks or tears are initiated in a tire they can only grow and if allowed to grow long enough or big enough you can end up with a separation in the tire structure.
Keeping moisture out of the rubber structure is why we also recommend you not park with your tires on wet sand or dirt and the moisture can migrate into the structure if exposed to water for weeks at a time.
Please don't jump to conclusions and say "Ya but I drive in the rain" or "Occasionally it rains and my tires get wet".  I am not talking about a few hours of exposure or even a few days. If you drive and heat up the tires it will drive the excess moisture out of the tire. It is weeks or even months of parking in a wet situation that we want to avoid.
Not inflating your tires with wet air (if you get water drops spitting out of the air hose it is way too wet to use except in an emergency) is what we would like to do. If you remove your valve core and what looks like fog or steam or water droplets spits out you have too much water in your tires and this is under high pressure all the time so this can affect the life of your tires.

Many after market tire sealants are water based so using that stuff can hurt your tires.

So that is why inflating your tires with dry or at least drier air is a good practice.


Friday, April 24, 2020

Contain tire Blowout?

Every few months someone posts a question on one of the numerous RV Forums I monitor, asking if it is possible to prevent the damage done to the RV when a tire fails and has a belt separation or comes apart from a sidewall Run Low Flex failure.

 I have previously written on the idea of trying to "contain" tire failure on my blog but for those that missed the information here is a summary and links for more details.

In the tire industry, we have test drums surrounded by steel grating which weighs 6 to 10# per square foot so don't forget you would need a substantial structure to support a 200# - 500# "shield over each tire position. This extra weight would also significantly decrease the amount of "stuff" you can pack into your RV.
 IMO having worked around tire test labs, an effective "shield" on an RV is unlikely to work. I feel that prevention is a much better approach.

To better understand the problem I suggest you review the following.

1. Read this post.

2. This post shows the kind of forces we are talking about.

3. Check out the safety cage around this tire test machine.

4. Buy, program and test a TPMS

5. Every 2,000 miles or annually (whichever comes first) do a "Free Spin" inspection of trailer tires.

Prevention is much better than and less expensive than trying to protect your wheel wells.

Friday, April 17, 2020

Tire industry magazine announces expansion of SAILUN brand

Modern Tire Dealer, a trade publication posted this information on Sailun brand tires.

  I do know that there are many RVs running this brand in 16" and 22.5" sizes and thought this information might be of interest. 

Sailun Will Expand Passenger, Truck Tire Plants

Posted on March 11, 2020

Sailun Group Co. Ltd. has started major expansions at its production facilities located in Dongying and Shenyang, China.
“The project expansion will focus on plans to equip these additional production lines with the latest cutting-edge manufacturing and testing equipment, as well as increasing IT capabilities to meet domestic and global customer needs,” according to Sailun officials, who add that intelligent manufacturing and the application of big data will be the focus of the both expansions.
“Each facility will be equipped with the world's most advanced production equipment and fully automated tire logistics lines, aimed at effectively enhancing the level of automation, information, and intelligence of core equipment and enhanced AI in the tire manufacturing process.”
The Sailun Dongying plant expansion is a major strategic project for the Sailun Group.
After completion of the final stage, the factory expansion will allow Sailun to reach an annual production capacity of 27 million passenger tires.
The Sailun Shenyang plant expansion will focus on increasing radial commercial truck tire capacity and is also a strategic initiative for Sailun in 2020. Once complete, the plant will have an annual production capacity of more than five million truck tires.

Friday, April 10, 2020

Things to do while not traveling.

Ya it's really a pain to not be able to enjoy our RVs.

But There are a couple of "Projects" that may make life a bit better down the road.

Tire Inspection

Recording your DOT Serial

Testing your TPMS

Reading to increase your general tire knowledge.

First is Tire Inspection. Here we are focusing on possible separations. This is a bit easier for Trailers but also it may be more important for them because of higher separation rate. First off you need to be safe. This means ensuring the trailer or Motorhome can not move. It may be best to hook up the trailer to the TV and set the brakes. Motorhomes can use the parking brake and put the unit in gear. For either type of RV you should block the tires that are on the ground so the unit does not move.  Not everyone will be able to do these steps, but if you can, here is what I suggest.
Jack up one end of one axle (motorhomes this means one end of the front) You then want to place a reference bar or pointer or stick near the tire, then rotate the tire watching the space between the reference pointer and the tire. Do this for the side of the tread and center of the tread. If you can see the relative movement of more than 1/4" you have a suspect tire. Mark the location where the tire is moving outward. you might snap a picture where you can also read the words on the sidewall at the location of interest for future reference. You might even consider a 10 second video that shows suspect movement.  I cover the general visual inspection and have a youtube VIDEO in THIS post.  I have a series of posts with more details on tire inspection HERE.
While Trailer owners can do this for each of their tires Motorhomes are probably limited to just "spinning" the front tire and even then need a HD jack.  Remember if unsure or do not have a solid surface to work on, or the proper tools, you may not want to do this rotating inspection.

If you have a suspect location you should contact your tire dealer. If you have a video you can show them that. Since they can see the tire close up if necessary they are in the best position to confirm there is a problem or to say all is OK.

DOT serial. If you haven't recorded your full DOT serial numbers and kept that information with other important papers, this "downtime" might be a good opportunity when you have a nice weather day. Having this information might save you some time in the future if you hear there is a recall on your tire brand and size. Recalls are based on the DOT sericl and tires will be replaced for free if covered by a recall.

Testing your TPMS.  I bet almost none of you have tested your TPMS. This should be done at least once a year. Some nice afternoon when you have nice weather with your traveling companion in the driver seat. AND when you have access to air of high enough pressure to top-off your tires. Go to each tire and unscrew the external sensor and have the person in the driver seat let you know that they can see and hear the warning for each tire position.  you don't even have to completely remove the sensor. Just unscrew enough to hear air leaking out. As soon as the monitor in the cab sounds you can screw the sensor back in to stop the air leak. Once you know that every sensor works you then need to go around and add back in the 5 psi or so that leaked out.
Doing this will also confirm you have your low pressure warning level set properly as the warning should go off as soon as you lose about 5 psi. I cover how I suggest you set your warning levels in THIS post.

Finally, with all the time on your hands, you might consider simply reading through all the posts on my RVTireSafety blog. I don't expect you to remember everything but I believe that if you have reviewed the entire blog you will then know where you can go to get an answer to just about any question you might have on tires, tire pressure, valves, TPMS, weight and inflation.

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.

Friday, April 3, 2020

Side to Side Motorhome weight balance

Got this question and thought that others may have similar problem.

Hi I have followed your postings on this forum and I own 2017 Newmar Ventana 4002. I am trying to understand and resolve an issue with my coach where I have a 1000 lb difference in weight on the front axle side to side. I have had the coach weighed on all 4 corners 3 times and get the same results. My understanding and I think it may have been in one of your post that the difference should never been more than 500 lbs side to side.

I am having a conversation with Newmar about this and pushing them for answers why as I am well under the GAVR and well under the GVWR. I have unloaded and moved the contents in the basement and inside the coach around hoping to make a difference and the reality is I don't have much to move.

I am looking for any studies or evidence that I can show Newmar that this is not safe if indeed my information is correct that side to side should not be more than 500 lbs. I am hoping you might know of something I can get my hands on or someone I can talk to.

Thank you for taking the time to read this PM.

Sincerely,  Newmar owner.

My reply:

You may have misunderstood the side to side weight comments.

It is suggested that people get "4 corner" weights rather than just axle weights, as it is known that some coaches are unbalanced side to side.
We do this because if you only get axle weights and simply divide by 2 and assume your side to side weights are even, you could end up with an overloaded or underinflated tire IF the sides are not close to even.
Not sure where the 500# figure comes from other than looking at the load increments in the tables for each 5 psi. You will see that with some large tires the load capacity can increase by a few hundred pounds with an increase of 5 psi.

I do not remember ever seeing a "should" not be more than 500# different statement

You have confirmed that your coach is not balanced side to side and it appears you have made a good effort to get more balanced but have not been able to because of the design / layout of your coach.

With that in mind, and knowing the load on the "heavy end", you need to consult the Load/Inflation tables and use the heavy end weight to learn your MINIMUM inflation for all the tires on that axle. I still recommend you add 10% to the table inflation number as long as you do not exceed the max inflation rating for the wheels. This 10% helps avoid TPM low-pressure warnings due to an occasional drop in Ambient air temperature 

I trust you have confirmed with your RV Mfg that the wheels are capable of supporting the heavy end load.
I hope this clarifies what you need to do and answers the "Why" we suggest you get the weights on each end of each axle.


Friday, March 27, 2020

"Reserve Load" or Load Capacity Margin

Ran across a post on Reserve Load or Reserve capacity that suggested the RV owner had been given incorrect information. Here is the post and my reply.

Personally, I'd run LTs, simply because of their higher "reserve" capacity; upwards of 30% over the stated load. Given that STs have, at best, 10% (used to be basically 0%), you're still in ST load territory, with a much better tire. Hell, we used to run our old 1/2t trucks with massive loads and just air up to 60-65 psi and go. Yes, it wasn't very far, or very fast, but those tires still lasted 50-60k miles, usually with steel cord showing around the edges. :-) We'd then take them off and put them on a disk or trailer and use them until they sun-rotted.

I think someone miss-informed you about "Reserve Load".
All tires have a stated load capacity for example. "2,340# Max Load" molded on the tire sidewall at a stated inflation level such as  "50" psi.

"Reserve Load" is the difference between the actual applied load and the stated load capacity and is many times stated as a percentage

Example: A vehicle is on weight scales and we learn that a tire has 2200# load on the tire. The tire has a load capacity of 2,750#.   2,750 minus 2,200 = 550#   which is 20% of 2,750. It doesn't make any difference what type tire we are talking about as the math is still the same.

Now, it is true that for a given set of dimensions, e.g., 235/75R15,  the stated load capacity is different depending on type tire and inflation level.   P-type and LT-type and ST-type each have different stated load capacities at their stated inflation pressure. For this discussion, let's keep inflation differences out of the picture.

Let's look at a P235/75R15 at 35 psi is rated to support 2,028# ( In a trailer application P-Type must be De-rated by Load/1.1 giving 1,842# capacity.) An LT235/75R15 is rated for 1,530# @ 35 psi and an ST235/75R15 is rated to support 1,870#

BUT the "Reserve Load" calculation is still  (Tire Load Capacity)/Measured scale Load).

The 10% margin for trailers is the difference between the GAWR and the total capacity of the tires on that axle at their max load.  I have posted in my blog some actual margins showing that many cars have load margins of 25% to 35% while some RVs made before Nov 2017, when RVIA changed the "Margin" to 10%, had margins of tire capacity vs GAWR as low as 1%.

Hope this helps.


Friday, March 20, 2020

Response to some of my information and warnings on tire inflation

After posting on one RV Forum some steps that I felt if taken could result in longer tire life by lowering the Interply Shear Forces, I got this reply:
"Sounds like tires should never be used or stored in any configuration other than the 'as cured' state or they simply self destruct.
Gonna have to figure out how to make these R/Vs hovercrafts."

I offered the following:
A bit of an over-reaction. My advice is intended to offer a series of steps that can be taken to extend the life of their tires rather than actions or inaction that may shorten tire life.

One of the biggest problems is the inability to understanding the real "Root Cause" of tire failure. IMO too many simply assume that somehow, the zip code of the factory where the tires are made is a "cause" for a failure.
Have you read and do you understand the difference between the two major and different reasons (root cause) for failure as covered in THESE posts?

TPMS, when properly PROGRAMED and used  can essentially eliminate one of the two primary reasons for tire failure.

Having a good level (15% to 25%) Reserve Load is the second major thing people can do to get a more reasonable tire life. I would be very surprised to learn that tires with at least 15% actual Reserve Load didn't perform much better than the more normal 0% to 5% level.

Friday, March 13, 2020

Is the Goodyear Endurance ST type tire "Better Quality" than a Goodyear LT tire?

Had a couple of comments on my post on LT vs ST type tires for RV trailers

Alan said

"Now, I am VERY confused. For years, everyone in the RV business, its commentators, its experts and other blogger forums so-called experts “having used this or that for soooo many years without any problems”, etc, had me convinced in believing all the hullabaloo about the ST tire’s sidewalls being much better, much stiffer and much more resistant to the particular type of flexing that occurs when driving, turning and parking travel trailers or fifth wheels than LTs. After the appearance of the “china-bombs syndrome” a few years ago, people started to realize that practically all ST tires were manufactured in China anyway, whatever the
“US brand name” stamped on them, leaving the consumer with very few, if any, alternatives.
Now, co├»ncidentelly, we hear that LT tires are “just the thing” for trailering.
It also appears that a handful of RV manufacturers, like Jayco, have seemingly struck a deal with Goodyear, who now has resumed manufacturing ST tires in North America, to equip their new trailers with “US-made ST tires”. I guess their ST tire prices have dropped again enough to catch the big manufacturer’s attention and make it worth their while.
So I guess the real question should now be, are US-made Goodyear ST tires better, worst or equal quality than their US-made Goodyear LT tires, or why even bother to engineer ST tires at all? We shall see, in time, who wins between; Beta or Vhs, Plasma or Lcd, Android or Apple, etc, etc, etc."

Alain, The biggest issue is, I know of no way to do a direct comparison of ST vs LT tires other than an expensive tire test. We can't depend on the DOT test results. In all probability the tires all pass, simply because the RV industry and ST tire mfg companies were successful in getting ST tires excluded from the significant improvement in testing with updated standards in 2002. There is no question, in my mind, that the tests (FMVSS 571.119) for ST type tires are easier to pass than the tests (FMVSS 571.139) for new Passenger and LT type tires.
I have looked at the construction of a GY Endurance and it certainly looks better than the older Marathon design. Now remember I do not have access to the actual specification or material properties used by GY but in the Endurance tire line, they appear to have added a Nylon cap over the steel belts. You can confirm this by reading the material list molded on a tire sidewall.

"Quality" is a tough call when you have two different specifications to start with. Isn't Quality just a measure of a tire's ability to meet the specification for that product?

You can think of it this way.  If I had two pieces of chain. One rated at 500# and another rated at 550#. They both meet a strength test of supporting the rated load and if you tested 100 pieces of each and found that all 100 passes the rates strength test how would you rate the 'Quality"? You can't say the 550# chain is better quality than the 500# chain as they have two different goals, just as you can't say a 1-ton truck is better quality than a 1/2 ton truck because the 1-ton can handle more load.

Your example of Beta vs VHS is a good example of the confusion possible. Beta was judged technically superior to VHS but Sony made a marketing decision to prevent other companies from using the Beta specification in their video players. The result was that VHS units were less expensive so many people bought on price. Eventually, Sony lost out. Not because the "Quality" of that video format wasn't as good as VHS but because the market was "price-sensitive" and too many people selected lower cost over better quality product.

Gene offered
"OK, color me confused! I have always gotten the impression that ST tires and not LT tires are what I should be running on my RV. After reading this article now I’m not sure. Are you suggesting that all things being equal, LT tires of the same size, load rating, etc are better to run on my RV? I don’t mind the cost, just want to put best possible tire on my RV. Thanks for keeping us informed."

to which I replied

Gene, The problem is that "all things are not equal" as there are no LT tires of the same size, load range, and load rating, etc as an ST tire. There is always something that is different.
Sometimes the only option would be to go with larger size LT tires but in some cases, there is no physical room to run the available larger size tires.

IMO, what you "should" be running are tires built to the latest industry test standards (LT) that can offer at least 15 to 25% "Reserve Load " capacity

Friday, March 6, 2020

Is it against federal regulations to change tires on an RV?

I have been following a series of posts on RV Forums where people ask about changing tires [Size, Type, Load Range or cold inflation setting]. Occasionally I run across some people who have adopted a hobby of commenting on tires in RV application and with a little working knowledge, make pronouncements on the "legality" of making any change in tires, that I do not agree with.

Other times I see a question like this one;
 "My research (curiosity vs need) is that LT and ST tires are not sold in the same sizes, so changing RIMS would be required?"

Here is my reply

Some LT tires show the same "dimensions" for example (235/75R15) as some ST tires but the "Dimensions" are NOT the actual complete size "description" which includes the letters and numbers before and after the dimensions. i.e. ST235/75R15 110/105L LR-C  vs  LT235/75R15 110/107T LR-D.  In this example, the ST tire is rated for 2,340#@ 50 psi while the LT tire needs 65 psi tp support 2,335# (single load capacity shown) Also the ST tire is rated for a max of 75 mph while the LT is rated for 118mph operational speed

Yes there are some ST tires where the dimensions do not match any tire identified as an LT type currently on sale. This is where you have to do some research and learn some facts on what can be considered a reasonable and safe change in tire type or size.

The Key items to confirm:
1. Is the Load Capacity of the new tire equal or greater than to original tire when you consider your new intended cold tire inflation? This does not mean +/- 25#. It means "equal or greater"
2. Is the Speed Rating equal or better than the original tire when you consider your intended new cold inflation level? (yes some tire load capacities are a function of speed)
3. Are your wheels rated for the inflation level you intend to run with your new tires? This limit may not be easy to learn but wheels can fail from too high a pressure just as they can fail from too many pounds load. The pressure we are talking about here is always the COLD inflation pressure.

You may need to be smarter than the tire guy if you want or have to make a change.

Remember there are some who post on various RV forums who would tell you that you would be violating Federal Regulations if you change from a Goodyear Marathon made in 2016 to any Goodyear tire made in 2019.

While it is definitely true that some people make changes in tire "dimensions" or "type" or inflation level which IMO as an actual tire design engineer, I would consider unwise. BUT that does not mean you can not consider making changes as long as you follow the guidelines posted above that follow the published guidelines from major tire companies.

Friday, February 28, 2020

YES You do need "Bolt-in" metal valve stems with your TPMS

Story on a Sprinter RV forum.
Reply to posts on TPMS
"My new tire pressure monitoring system just saved our just-completed trip to Florida. Thanks to you all I thought I had, and paid a lot, to Mercedes to replace my rubber valve stems and add metal valve extenders for my sensors. If you remember, I did see the front wheel valves Mercedes did NOT replace with steel. I did get BORG valve stems from, as suggested, for the front and my local repair shop installed them. I could not see into the rear dual's to check. Well, you were right, after about 2000 miles into our trip, I turned on the TMPS to check pressures. The warning came up right away on one of the rear tires, 7 PSI. Sure enough, after five hours just off of interstate 75 in Florida, Mercedes had roadside assistance change to the spare (still have warranty). I added some air to the flat tire and soaped the rubber valve to verify that's what caused the leak. It didn't seem like a rub through but I did see cracks (must be from vibration). We drove 160 miles to a tire repair shop in Georgia. They put in small rubber valve stems in the spare and all four rear tires because I couldn't trust the rubber valves. All TPM sensors were removed from the rear wheels. Lesson learned, TIRE PRESSURE MONITORING IS A MUST ALONG WITH STEEL VALVE STEMS. Rubber ones will crack and leak. I will order BORG steel valves for the rear wheels."

I did offer a comment that you need the TPMS on for it to provide a warning and I was a bit concerned about the comment on "turning on the TPMS" to check tire pressure.

I am posting this comment to point out what can happen when you use rubber valve stems and an external TPM sensor.


Friday, February 21, 2020

Why inflate your tires to their max, when parking for long time?

I had a question about what inflation to run when parking your RV or vehicles for a long time. I initially said that would lower the Interply Shear.

Then, I was asked
"Could you explain interply shear on a parked R/V?"

Any time a tire is deformed (loaded) the cured rubber in the belt area moves away from the "as cured" shape. Even if not rolling, the area that is now flat on the road has been "bent" from the as-cured original curved state.
This bending causes shear (tearing) forces between the belts, which, at the molecular level, can result in bonds breaking between the carbon, hydrogen and sulfur atoms. If the bending is sufficiently large, the tear gets larger.
If you have higher inflation in the tire, the bending is less than when you have lower inflation which takes us back to decreasing the molecular tearing.
Other things happen too. "Cold Flat spotting" where a portion of the tread ends up flatter than the portion not loaded. This difference can result in vibration and shaking once you start driving. The "flat spot" also has to "work itself out" when you start driving. Again the change in shape when driving is rapid which can result in those broken molecular bonds. Slower changes in shape as when you inflate a tire allow the rubber to move or even "flow" a bit so the atoms have time to re-arrange.

If you ever played with "Silly Putty" as a kid you have experienced this effect. When you slowly pulled the putty it would stretch but if you yanked it quickly it would break. Silly Putty is a form of synthetic butadiene rubber which is very similar to the synthetic rubber used in tires

The whole concept of getting a longer tire life and better belt durability is to decreases these shear (tearing) forces that come about because of the changes in the shape of the belt package.
Now I don't expect people to inflate your tires every night or even every time you go camping for a few days. But if you are parking for a month or more over the Winter, it might be worth the effort. Only you know how much effort it would take to adjust your tire pressure and if you think a few extra weeks or months of tire life is worth the effort.


Friday, February 14, 2020

Heat, High Speed and the "Magic" in ST tires.

Heat generation is primarily the result of a combination of High Speed, High Load, and Low Inflation. Factors that can counter some of the negative effects of heat on tires can include the use of more expensive rubber compounds, reduced thickness tread and other construction features that are out of our control as tire owners. Without access to secret formulas and other proprietary information, I know of no way to learn which of these features is in which tires if any. There is one exception, of the inclusion of full Nylon Cap Ply. This would be identified in the material list molded on the tire sidewall along with the number and material in both the sidewall and under the center of the tire tread.

However, the driver] has complete control over the Speed/Load/Inflation factors.

IMO it would be better if all tires had at least a 15% margin on load capacity, with 20 to 25% being better margin. We need to remember that road slant & crown and curves along with significant sideload from wind can easily result in overloading tires that were measured on a level scale. Multi-axle trailers should shoot for a 25% load margin. (read about Interply Shear to understand why )

Ever wonder why RV trailers seem to have a lot of tire problems but your daily driver (car or SUV) doesn't?
Let's look at Reserve Load Capacity of your car:
Many / most have 30% to 40% Reserve Capacity on the tires.


Now when we look at an RV trailer we see only 6% with many having 0% margin.

 If we assume we want to have 25% Reserve load capacity on the above RV, then 13,290/(Tire max load X 4)= 0.75
and each tire max load shall be 4,430 lb.    So the right choice would be an all-steel
ST235/85R16 132/127 (14 with a max load of 4,410 lb.)

Previously I indicated that Inter Ply Shear can be the equivalent of adding 24% more load on the tire while in operation. Using the above tire the IPS effect is reduced considerably.

NOTE in 2017 RVIA and the National Fire Protection Association, guidelines for tire selection for RVs was updated to require a MINIMUM of a 10% margin in tire load capacity over the GAWR. Some RV companies achieved this margin by upgrading their tire load capacity while others simply lowered the GAWR number on the vehicle certification label. Do you know what your RV company did?


Speed rating. We should think of this like the engine red-line. Everyone seems to understand that running faster than red line will shorten engine life but that doesn't mean that 5,900 on a 6,000 redline is good to run for hours on end and may contribute to shorter engine life just as running 62 mph on tires rated, based on their original load calculations, for a max of 65 mph.
The high-speed test is a 30-minute step speed test of a brand new tire on a smooth test wheel. No potholes or curb damage. All that is needed to "pass" the test is to meet the target speed and not come apart. The tire is considered scrap after the test.  Would you consider your tires to be "scrap" after you run 70 or 80 mph for an hour or so?
Remember damage (internal cracks) done, even at the molecular level, in tires never repairs itself but only increases in size.

While this post is primarily about Trailer application the limit on high speed also applies to 16 through 22.5" tires that have a max rating of 75 in RV application which would be their "Red Line" but I hear many Class-A owners talking about running over 70 for miles on end but being surprised when they suffer a tire failure.

LT tires would be my first choice in any trailer application where heavy loading was required. I do not understand why so many think that there is some magic engineering used on ST tires that allow them to support 10% to 20% more load than an LT tire of identically dimensions. The load formulas used today for ST type are the same ones used in 1969 when they were limited to 65 MAX (red-line).

I would be very interested to hear an answer from the engineers at the companies that make ST type tires why they were able to suddenly, almost overnight, increase the speed rating from 65 to 75, 87 or even 99 on their ST type tires. Do they have some new materials? Why don't they put those same super materials in LT tires and increase the load capacity of LT tires to be the same as or near to the loads seen claimed for ST type tires?

Sorry, I just don't buy the new claimed high-speed capabilities of ST type tires that exceed the load and speed capabilities of equal size LT tires.


Friday, February 7, 2020

Air Compressor - How Big do you need?

While air volume output might be a consideration, IMO if you are properly inflating your tires and properly (TPMS) monitoring inflation I don't understand how anyone can get in a position of needing more than about 5 psi unless you have an active leak.

If you are only adding 5 psi then tou do not need to worry about how long it would take to inflate a 275/80R22.5   All you need is a compressor rated for more psi than what your tire needs. I would think that a 150 psi rating for the compressor fro tires needing 125 psi   or 100 psi rating for 80 psi tires would be enough.

As I have covered a number of times in this blog, I recommend your cold inflation pressure to be at least 10% above the minimum needed to support your actual measured tire loading (Minimum inflation would be based on the heaviest loaded tire on any axle or lacking individual tire loading numbers,  then using an assumed 53/47% side to side split for motorhomes and trailers with big slides or residential refrigerators and at least 51/49% load split for smaller trailers)

So assuming you have LR-C or LR-D tires you would be inflating to 50 or 65 psi with your TPMS warning set to no lower than 49 or 64 with your minimum inflation in the load tables being 45  and 58. So how would you ever need to add more than 5 or 6 psi assuming you let your tires get that low? Why not do your "top-off" as soon as you need 3 psi? Now you do need to consider the 1 or 2 psi difference between your calibrated hand gauge and the TPMS reading. I set the warning based on the TPMS reading AFTER setting the tire using my certified hand gauge.

Yes pressure changes with temperature (about 2% for change of 10°F Temperature)  A change in morning temperature of 40F from day to day is unusual and that would only result in a pressure drop of 5 psi on your LR-D tires.

Motorhomes should be running a +10% margin on air pressure based on the measured tire loading which means there would need to be a 50°F drop in temperature for them to need to add 10 psi (assuming a 100 psi minimum).

If you need to add more than 20% (20psi) of the needed pressure in your tires with steel body ply, that means you have technically been operating on a "flat" tire according to tire industry standards and you should have a professional inspection and have them re-inflate your tires AFTER the reason for the sir loss was identified and repaired. Large 19.5 and 22.5 tires should only be re-inflated in a cage just in case there was damage to the steel body cords which can lead to an explosion due to zipper rupture.

LR-E (80 psi polyester body tires) as found on most Class-C and some larger trailers need to consider the above information and adjust for their higher cold inflation numbers. I would consider a 20% drop to put you in the safety cage re-inflation level if you drove on the tires when that low. While they are not likely to suffer a true "zipper" failure from fatigued steel body cords, there can still be internal structural damage to your tires.

Bottom Line:  Monitor your tire pressure and don't let the pressure drop more than 10% before you re-inflate your tires. Know why the pressure dropped and if not due to a drastic change in temperature overnight, inspect for leaks. I find that spray cleaner like Windex or other cleaners tend to foam at the location of the leak.


Friday, January 31, 2020

RV Tire warranty. How do engineers "read" tire conditions?

Read the following on an RV forum
"Carlisle Tire's warranty used to state "tires must be inflated to sidewall stated pressure or warranty is void"; I don't know about now though.
How in the world do they determine if the tires are inflated to sidewall pressure? Is there a little gremlin with a report card in each tire. Some manufactures just never get out of the box.
Unless it was a bad tire, had been run flat previously, and most likely a bunch of other possibilities.  At the time of a blow out there is no way they would know other than by assumption.
Yes, most probably operator error, but only assumptions."

Sorry, but there are ways to identify the probable inflation & load history of a tire. Just as a Medical Examiner can do an autopsy and identify the signs of bad diet and poor or no exercise, or years of smoking, it is many times possible to see the physical signs of low inflation and high load.

These signs can show up in the indentation into the tire left by the wheel.

Here are examples of improper inflation or a Run Low Flex Failure of a P type, ST or LT type tire.

Melted body cord is physical proof of extreme run low 

Also, the different flex markings can be seen on the interior of a tire. In extreme cases the Innerliner (special rubber that holds air in much like a tube did in tube-type tires)

Manufacturing "Defects" will usually result in early life failure i.e. <1,000 miles.  Tire failure is in itself not proof of some nebulous "defect" even though lawyers and those not experienced in failed tire inspection want to think so.
Once you examine, in detail, a few thousand tires from both controlled testing and from day to day use & abuse the conditions seen in tires tell a story of the tire's history.
Too often people simply think of the conditions (load, speed, inflation, road) at the moment the tire fails as the "facts" to be considered when trying to decide the "why" a tire failed. In reality, the damage might have been done hours, days or even months earlier.
See THIS post on a study of pot hole damage and how long it took for some tires to fail from the impact.

As I point out in my "RV Tire Knowledge" Seminars at RV Conventions, tires are like potato salad, putting the salad back in the refrigerator after it was left for hours in the hot sun does not "fix it" and make it good to eat the next day any more than taking the burnt hot dog off the grill and letting it cool down before serving it makes for a good meal. Adding the correct air in a tire after running it low for thousands of miles, does not repair the damage. Slowing down to 50mph after hours of speeds of 70 to 80+ over the preceding weeks and months does not "fix"  or heal the thousands of microscopic cracks that were formed in the overheated and overstressed belt rubber. Once a crack is initiated it does nothing but grow. If a person stopped his smoking addiction of 2 packs a day for 40 years a couple months ago, will his lungs be clean and clear today? Not a chance.

When examining a tire, I look at the physical condition of a tire and specifically what evidence there might be. Years of experience has taught me what to look for and allows me, as a court-certified "Expert", to form an opinion that is based on the examination of many thousand tires.


Friday, January 24, 2020

I bleed off the high air pressure so I don't exceed the "Max Pressure"

The above statement or a variation of it seems to be made about once a week on one or another of the various RV forums I frequently review. It appears that many people incorrectly believe that exceeding the 'Max Pressure" number molded on the tire sidewall is going to result in tire failure and explosion.
It may help to let people know about some of the testings that tires undergo during the development phase.

First some background. The "Max Inflation" statement on your tire sidewall really is the inflation associated with the Maximum Load capacity. If you actually read your tire sidewall you will see that is what it says. So the number of PSI is really the minimum needed to support the stated load. It is important to understand that we are always talking about the "cold" inflation and not the inflation of a tire that is running down the highway or has been in direct sunlight or driven on in the prior couple of hours. "Cold" inflation does not mean the tire needs to be refrigerated but it means the tire is at the prevailing Ambient temperature.

With the introduction of aftermarket TPMS that report both tire pressure and the temperature of the sensor, people are now being exposed to numbers, they have no experience with. They see tire pressure rising as they drive down the highway. Some may see a 10% rise in pressure from the pressure they set their tires to just a half-hour earlier. Others may see a 20% or even a 25% increase in pressure and for some, this increase was a cause for concern. Not because they had any working knowledge of tire operating temperature or pressure but simply because the pressure was higher than they expected. A few people have decided that they need to bleed down the high pressure because they thought the pressure number of the tire sidewall was the max it should ever see.  Of course, the action of bleeding down the hot pressure was exactly the wrong thing to do as that meant that the tire would no longer be operating at the pressures expected by the tire engineer when they originally designed and tested the tire specification.

Obviously, this raises the question of how much pressure a tire can tolerate before the owner should be concerned. Well, I am going to give you some numbers but these are only examples. I cannot speak for every tire companies process of specifications but if we start with a few guidelines I think you can get comfortable and hopefully, you will believe that tire design engineers do have a reasonable idea of what they are doing.

First off we are only going to discuss regular production street tires that have passed DOT testing. The numbers I will use would basically be seen on new tires. I cannot advise on a tire's capability after it has been damaged or run for many thousands of miles. Damaged tires can fail when re-inflated as seen in THIS video. Heavy truck multi-piece rims MUST be inflated in a safety cage. If you suffered a puncture and drove any distance with the tire underinflated you may have permanently damaged the body cords which is why you should always tell the tire service person you drove on the under-inflated tire so they know to use a cage or other restraining safety equipment. Age and miles can reduce the strength of any tire but we do consider this degradation when approving a design. Another consideration is the availability of high-pressure air. Most home compressors or those that supply air to hoses made available to consumers have an upper limit of about 150 psi so we don't expect any consumer to have access to or to use industrial air pressure which can be 400 psi or even special inflation units as used on aircraft tires.

Basically many tires are tested to 300 to 400% of their rated inflation or above 200 psi whichever is lower. I had a number of tires that could contain over 300 psi when new but if they had been damaged the same tire might fail at less than 200psi but I also never, in my 40 years saw a tire fail from normal pressure increase and I was involved in the testing and evaluation of thousands of tires.

The BOTTOM LINE is Please do not bleed down your hot inflation pressure. You should ONLY set and adjust inflation when the tire is cool and at Ambient temperature. Doing otherwise MAY result in you having a failure days or weeks later because you were running lower pressure than what was needed for the tire load you were applying.