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Friday, December 27, 2019

I run TPMS but the tire still came apart. Why?

I found a post from a fellow RV owner who has a TPMS but still had the tire come apart as seen below.

The tire in the picture shows clear signs of a "Run Low Sidewall Flex Failure" i.e. that sharp line around the sidewall with the melted body cord showing.
Yes, the driver got a warning of air loss but I wonder what the Low-Pressure warning level is set at, or if the system has a "rapid air loss" setting.

The "melt line" takes a few miles to develop with significant loss of air (maybe 25 to 40%) while still running at highway speeds. Just driving a mile or so with a 10% loss as you slow down to pull over is usually not enough time to get the body cord to the 350 to 400F required to melt the Polyester cords.

As I have covered how I program my TPMS in this blog back in August 2017. I suggested that the Low-Pressure Warning level be set such that the driver gets a warning as soon as the pressure has dropped to the pressure needed to support the tire load based on scale load and tire Load / Inflation table numbers.  Hopefully, those who subscribe to the blog or those who have gone back and read the posts followed my procedure and have adjusted their TPMS settings according to their RV vehicle needs.
This may take a little thought and effort depending on the brand TPMS. Some may allow you to directly set the low-pressure level while others may require you to calculate the required "set" level as they have a fixed percentage of air loss before they start the warning "beep".

Some systems provide a warning as soon as just a few psi is lost (from the higher hot pressure level) from a puncture.
Example  Your cold set pressure is 80 based on a minimum required inflation to support the load of 70 psi.  When running down the road at 60 mph your tire is probably at 88 to 90 psi. If your system only warns with a 25% pressure drop from the "set" pressure that means you can travel many miles before you get a warning at 60 psi. At that point, you have overloaded your time for many miles.
"Early Warning" or "Rapid Loss" feature might warn you as soon as your pressure drops from 90 to 87. This allows you to monitor the pressure as you look for a location to pull off the road.
TPMS is a powerful safety device but to get the maximum benefits it provides you need to do a little more than just screw the sensors onto your metal valve stems.


Friday, December 20, 2019

Are there stupid questions about tires?

Recently ran across a thread where there was a rather basic question on inflation where someone claimed to have "searched everywhere" to find how much pressure to put in his tires.

After dozens of posts on this blog, I have to admit I am disappointed that he hadn't found any of my info. I do know that many times a simple Google search on the tire-related topic will show this blog a few times.
There are no stupid questions. Ask questions and learn something new every day. But clearly, stupid answers are a real possibility.

I sort of agree but do wish that more people learned how to use the "search" function on forums as many questions have already been answered more than once. Also, learn how to efficiently use Google.
My problem is that I simply do not have the time to answer the same question multiple times a week.
For example "How much air do I need in my tires?"

When it comes to Motorhome tires and inflation it doesn't make any difference if your MH is blue of silver. The way to learn how much air the tires need is the same.  Without making a minimal effort to learn what to do and simply expecting someone to give you the proper answer i.e. "You need to inflate your tires to 94.565 psi" is not the correct answer.

The saying about teaching someone how to fish rather than just giving them the fish applies here.
How do we "teach" people that they need to learn how to search the Internet as the answer to most questions is already there?

 I am pretty confident that with over 400 posts I have at least touched on just about any question people might have relating to Tires or valves in RV application.

 If I have missed a topic please feel free to send me an email (address is shown under my picture on the right).

I do hope we all have a Happy and tire problem-free Holiday.


Friday, December 13, 2019

How I avoid problems with Dualie tire hose extenders.

The key to avoiding problems with a hose or any type of valve extension is to be sure the outer end is

 S O L I D.

Some hose kits come with small brackets that can be pop-riveted to hub cap. Others have brackets that attach to lug nut.
People often fail to support the hose or bracket when checking or adding air. The force needed to get a good air seal is enough to bend or loosen the hose mounts. or they inadvertently twist the hose and end up with a leak where the hose screws onto the metal valve.

You need to hold the outer end of the hose firmly to prevent movement or twisting or you can expect to eventually have problems.
In THIS blog post, you can see my set-up (42,000 mi) w/ no leaks or failures.

Since I run a +10% psi margin over the minimum pressure I need on my Class-C based on 4 corner weights and since I always run TPMS (that I have tested) I simply use the TPMS to tell me the inflation each morning before I start out.
During a cross country trip OH > OR > OH over 7 weeks I only needed to add air once so since I am not messing with the hose extensions, I am not pushing on their mounts or applying a force that might result in a slow leak.

If/when I ever do need to remove a sensor to change a battery or add air, I ALWAYS spritz Windex to check for any leaks after I am done.


Friday, December 6, 2019

The tire was "Defective"

Originally Posted by tap4154 View Post
They are now defective tires and should be replaced under warranty. Heck, maybe the dealer even knew they were defective? Do not let the dealer or Goodyear get away with not replacing them for free. BTW that the dealer even suggested putting the defective tires on the back tells me they may be shady...

I suggest you look up the definition of "Defect".
A belt separation in a condition that has a cause. The cause may be a defect such as some contamination was built into the tire between the belts or the wrong rubber compound was used on a batch of tires, as I discovered when inspecting tires back in 2000. As I pointed out in THIS post there are also external usage factors that can contribute to the initiation of a belt separation.
If you worked in a coal mine and after 30 years were diagnosed with "Black Lung" would that simply mean your body was defective which would make the condition your parent's fault?

If you had a sidewall flex failure due to running with only 20% of the air pressure required to support the load is that an indication of the tire being "Defective". You can learn more about this condition by reviewing THIS post in 2011 on Sidewall "Blowouts".

Simply claiming a tire is "defective" is the go-to excuse used by many that have no working knowledge of or don't want to spend the time investigation the "Why" tires develop various conditions.

If you have a tire failure and even if you don't know why it failed. Even after reviewing the posts on this blog that identify various reasons for a tire to fail, I still suggest you file a complaint with NHTSA. Please however just describe the condition of the tire and be sure to include the vehicle VIN and the full tire DOT serial.

Friday, November 29, 2019

"4-Corner" or CAT scale ?

Was reading a thread about scale weights on one of the RV forums.

OK Tireman9 here, an official card carrying member of the "Weight Police"

Seriously, some comments.
RE the Original Poster's  numbers. I would really be interested in learning the individual numbers from anyone who has done "4-corner" be it Escapees, RVSEF, on a closed State scale, State police portable or homemade scale.

The primary reason for 4-corner is not to get concerned about a 250# (5%) difference in individual tire position weight but to identify the outliers with 1,000# difference side to side which I am told is not that unusual.

I have posted several times both in my RV Tire blog and on various RV Forums that until you get confirmation with side to side weights that I suggest you assume a 53/47% side to side weight split. I have received scale numbers from a few folks and they were +/- 1% from the 53% figure for the heavy end of the axle. I have had 4-corner done 3 times (RVSEF and State Scale) and my Class-C runs at about 51.5% to 53.1% heavy for the heavy end of my 2 axles. I have also done a couple CAT scale readings just to ensure no significant "weight creep".

RE doing 4-corner on CAT. This is against CAT corporate policy as they say loading the platform way off-center can affect the scale accuracy and calibration. If you look around you will see that many CAT scales now have guard rail near the platforms to prevent off-center weights.

While I haven't looked at the Escapee scales, I have compared the RVSEF scales with some State Police scales and they appeared to be the same units.

The whole objective of getting tire weights is to avoid overloading your tires. No, your tires aren't likely to "blowout" if you have an extra 1% on one side vs the other, but if you discover you are at or above the load limit of your tires by 10% then you are really "consuming" the tire life faster than you might expect. This can result in a belt separation if you also push the speed rating for your tires in RV service (75 mph max).

Most folks never have belt separations on their cars but we all know that many RV owners have tire problems. One of the main reasons for this difference is that most cars are running around with 25% to 35% reserve load and are driving 20 to 40 mph below the tire speed rating for regular auto usage.
RVs, on the other hand, are running with 5% or - 10% reserve load and from 15 below to 15 mph above the speed rating for their tires when in RV service.

To address the calibration issues both with scales and pressure gauges. My Gauge tests find between 8% and 15%  are off by more than 5 psi with a few reading about 10 psi high which means that those owners were running their tires significantly underinflated.

All of this is why I suggest adding 10% to the minimum inflation required to support the load when you consult the tables after you use the heavy end of a 4 corner weight or the 53% figure from a CAT scale.

Thursday, November 21, 2019

Are sidewall cracks the cause of tire failure?

Read an RV forum post about sidewall cracks. From the picture, it appeared the tire had what I would call Ozone or UV cosmetic cracking. The owner was concerned about the tire durability as he had suffered a couple "Blowouts" previously.  I responded....

"Not being able to inspect the "Blowout" tires or even see some pictures, I have no idea for the reason for the tire failures as "blowout" is not specific enough to suggest a possible cause. They might have been run for a few miles while losing air. They might have suffered impact damage 10 or 100 or 1,000 miles prior to the ultimate failure. They might have been run overloaded or underinflated or over speed recommended by tire manufacturer or tire industry engineering guidelines for thousands of miles.

Yes, tire failures can be expensive if the failure is only discovered by operating the tires at speed and not during the regular detailed close inspection by a "qualified specialist" as outlined in the Michelin Tech bulletin on RV/Motorhome tire inspection.

It is also true that sidewall cracks, in my professional experience, are not in themselves the root cause of tire failure. Just as a person developing a temperature of 101F or 102F is not the cause of an illness but is just an external symptom. Tire sidewall cracks are an indication of extensive tire age with the cracks developing due to time, temperature, flexing and exposure to Ozone and UV. All of which are detrimental to tire life.

"Zipper" sidewall failures of steel body ply are the result of fatigue from operating for miles when significantly underinflated or overloaded or a combination of those. Sidewall crack inspection guidelines published on pg 8 of THIS guide, suggest a maximum depth of about 2/32" on large radial tires (22.5" sizes) which usually have rubber thickness closer or thicker than 0.10".

Tires "Fail" for two basic and different reasons:
1. Sidewall Flex failure from low inflation/High load
2. Belt separation from long term rubber degradation due to excess heat and age

I covered these in two separate posts in 2012  and again with a slightly different focus in 2014.

While I can conceive of someone running tires for many miles with sidewall cracks that get deeper than 2/32", those cracks would need to penetrate deeper and get completely through the sidewall rubber to the depth of the steel and then water would need to be introduced and enough time pass to allow a significant portion and number of steel cords rust and be weakened before a "Zipper" like failure could occur.

The above would, in most cases, take many months of operation and would require that no or improper or incomplete inspection take place before a tire would suffer a catastrophic failure.

So the bottom line is two-fold.

1. Ensure you are not overloading your tires and that they are ALWAYS inflated to what is needed  for your application by running a TPMS

2. Starting at 5 years (3 years in trailer application) from the DOT manufacture date molded on the tire sidewall and annually or every 2,000 miles whichever comes first, have them inspected.  I have covered the topic of inspection previously.


Thursday, November 14, 2019

Emergency equipment - Change a tire?

Was following a thread on the use of the special "tire lifts" similar to those seen here.

 One person discovered that the ramp they had purchased did not work on their model RV.

This points out the importance of testing and confirming that your "Emergency" equipment will actually do what you expect on your RV.

It doesn't make any difference if it is a ramp or folding ladder or an "X" wrench to get the lug nuts off a wheel if you get a flat, or some electric meter or other test instruments.
It's ALWAYS better to confirm you know how to use the tool and to confirm you have the strength if needed or the necessary knowledge to actually use the emergency device.

I learned this the hard way with a "bottle" jack that was too tall to fit under the axle of my Class-C RV.

I remember when I first started to drive my dad told me that before he would lend me his keys, I had to use the factory "lug nut bar" to loosen the nuts. Then figure out how to assemble the "bumper jack". Get the spare out of the trunk, remove the tire from the axle then put everything back where it belonged. I probably spent an hour working on it the first time but I did learn how to do every step correctly. ( he let me know if I was doing something wrong a\or in an unsafe manner ).

Friday, November 8, 2019

Should ST tires be outlawed?

A post on an RV forum caught my eye
"In 2014, when I bought my RV Trailer, I immediately went to Discount Tire for 6 Michelin XPS Rib truck tires. I don't baby them, I barely pay any attention to them, they've never been at 80 psi, and they have been wearing fine for 5 years. Been all over the US with no issues. Yet I see new trailers coming into the dealership where I work with blown tires just coming from Indiana. Chinese bombs need to be outlawed."

It's unlikely they will be outlawed given the price sensitivity in the RV market. With so many folks buying when the quoted price is just a monthly amount that is so low they will always be "underwater" on their purchase. The RV industry seems to only focus on making the sale and as long as it feels it can only make the sale by offering the lowest possible price the industry will fight tooth and nail to not have to spend an extra $100 on a set of tires that can provide better durability.
In 2000 after the Ford Explorer recall both Passenger and LT type tires were forced to meet newer, tougher quality & durability standards as required by the "TREAD Act" but I believe that because of pressure from the RV industry, ST type tire requirements were excluded from the new requirements as complying would have increased the cost to the RV company a few bucks and they simply didn't feel they could stay in business if they had to increase their prices.
So we are stuck with tires built to 1970 quality and durability levels.

IMO Until or unless the RV community in large numbers, demands an improvement in the tire quality with an update & upgrade in the performance standards required by DOT there will only be improvements on a small number of models that offer ST tires with more Reserve Load or offer actual LT tires. How many RV owners have made the minimal effort of filing a complaint on a tire failure to NHTSA? Or written a letter to the  Administrator of NHTSA?     U.S. Department of Transportation,    1200 New Jersey Avenue SE.  Washington, DC 20590

When was the last time you heard someone not ask about buying tires at the lowest price? Or walking away from a sale if the dealer didn't provide better tires OE?  or the dealer didn't offer a multi-year warranty on tires that came on the RV?

A review of some comments on this forum shows the truth in what I am saying. The new Goodyear Endurance seems to be providing a significant improvement in tire durability for ST type tires but we see several people stating they are not willing to pay the price.

If you are only willing to pay Harbor Freight prices for your tools why would you expect SK, Milwaukee, Proto, or MATCO quality?

From day one ST type tires were introduced as a low-cost option to higher cost Light Truck type tires when comparing Pounds load capacity per dollar cost. We also had the 55 mph National Speed limit so offering tires with a 65 mph max wasn't a deal breaker

Friday, November 1, 2019

Spare tire - mis-matched size What to do?

Class-A owner said:
"I use to advocate carrying a spare in my 2005 Monaco Diplomat. On that coach, it used a short 22.5 tire and it fit in my pass thru bay, unmounted. I could stuff a lot inside the tire and didn't lose much storage. Fast forward to my current RV and the 315's won't fit in a bay.

So......a lot of people say to just carry a spare, including a trailer owner with a rear mounted spare. It's nice to say and actually nice to carry a spare if you have room, but if you don't have the space, you need another plan. That plan is to have a roadside service plan and be willing to accept an odd sized or used tire to get you back on the road. Wait until you're in a major town on a weekday to resolve the issue with a new or correct size."
My reply:
While using an "odd" size on the front might get you moving (slower) mismatched duals will mean the larger OD tire is carrying more than design load.
I would limit the speed to 50 or less and be prepared to scrap BOTH tires as the internal structural damage is impossible to "inspect" for.
If you have two different size tires on your RV and can only carry one I would suggest the rear. Hopefully, you have confirmed your actual load on each tire position and have some margin available on the fronts. If you are running at 100% front capacity (bad idea) then the use of a smaller "rear" tire as a temporary front means you really need to limit both speed and distance you operate in that situation.
Overload does not always mean tire belts will overheat and a warning is received from your TPMS. The steel sidewall ply can fatigue from over deflection and you will have no warning and not know it till the sidewall fails catastrophically. 

All the above brings up the question of why did you have a tire failure in the first place?. Have you read THIS post.

A properly programmed TPMS should provide an early warning as soon as you lose 15% from your "set" pressure (slow leak) or 3 psi from your hot pressure within a couple of minutes (fast leak).  If you are also having a tire professional do a close and thorough inspection every year starting at 5 years for Class-A and Class-C or at 3 years for any trailer, it is unlikely for you to develop a belt separation without some advance warning.
Taking precautions is always better than trying to "fix" the tire after you have a flat.
NOTE. The above in no way should be taken as a suggestion that driving on an overloaded or under-inflated tire or mismatched duals is a safe thing to do. I am just offering suggestions for possible responses in an EMERGENCY situation where you feel you MUST move from your current location to a safer one.

Friday, October 25, 2019

New Truck with old Trailer, Sway (Stability) issues

I was asked by the moderator of an RV trailer forum to jump in on the topic by one of the members. Here is my response. I thought the info might be of interest to others.

My prime area of expertise is on tires, but I have also done extensive long-distance towing with a C3500 (454 gas) Dually with an 8' slide-in camper in the bed and pulling a 26' enclosed trailer with a  Camaro race car,

 tools, etc inside. I have towed from OH to FL and Calif and even made a trip on the Blue Ridge Pkwy while towing the race car trailer so I think I understand the handling situation of a loaded truck and trailer.

Some observations on info in some of the posts in this thread.

"P" type tires on the TV should be an indication that the TV should probably be limited to single axle "pop-up" or small boat trailers. It is important to remember that P-type tires must be "de-rated" in load capacity by 10% as they are not intended for truck or trailer application. Multi-axle trailers almost always indicate the need for a real truck (not just something that looks like one) This would mean LT type tires and 3/4 or 1-ton vehicle rating.
HERE is a good post on how to match a Truck & Trailer. It is much better to do a little work and learn the ratings of both your truck and trailer than relying on the salesperson telling you that you can pull a 5-ton trailer with a Ford Ranger just so he can make the sale.

P vs LT type tires. No, they do not make tires "between" these two types. If there is no P or LT before the numbers in the size then it is what is known as a "Euro-Metric" type tire and with an inflation of 36, it is definitely a P-type tire.
The P and LT and ST designations are found in tires designed and intended for highways in America. The inflation level molded on the tire sidewall is the give-away.

35 or 36 is standard Passenger type tire
50, 65, or 80 or higher is an LT type tire or a trailer only ST type.
In Europe, they use a "C" after the size to identify "Commercial" use i.e. LT. Don't confuse this with Load Range C which is the US Light Truck Load Range (old ply rating)

Tires marked "XL" or "Extra Load" are Passenger type tires (Max infl. 42 or 51 on some) that aren't quite LR-C Light Truck tires. This type was originally intended for "Station Wagons" which have been replaced by SUV but are many times used on light duty trucks as a cost-savings measure. (Passenger are really LR-B or "standard" load except for the XL passenger tires, but none say LR-B)

Vehicle "Sway" is a function of the tire inflation and the suspension design and vehicle loading. When inflated to the sidewall pressure there can be different sidewall stiffness but the difference should not be significant within the same Type tire and same Load Range.

Weights. Empty weights are really of little value in determining what will run down the highway safely. Fully loaded and hooked up individual axle loads are what is needed. With trailers (and motorhomes) it is even better to know the scale weight on each individual tire position when the vehicles have been loaded to their heaviest, as many RVs have been found to be 500 to 1,000# out of balance side to side. No, you don't have to get on a scale every trip but should have at least one set of readings when fully loaded.

Increased tire inflation will almost always result in improved stability.

New Tire "squirm". When you apply any new tire to any vehicle you may notice for the initial 100 to 200 miles less stability than on the tires you just took off. This happens for a few different reasons.
1. All tires have a "release agent" that allows them to be removed from the curing mold. This is a slippery substance that will wear off in a few miles.
2. When you buy new tires you are not making a clean, apples to apples comparison. You, as the driver, are comparing a worn older tire with a new full tread tire. Even if the tires were identical in construction and rubber compound you will get crisper and more solid handling with a worn tire (less tread) than a new (more tread) tire. In car racing, our tires may only have 2/32 or 3/32 tread depth while new tires come with 8/32 to 12/32 or more tread depth. In some classes of racing that require the use of "street" tires new tires have most of their tread "shaved" off with the express purpose of improving handling.

Getting scale weights. While you may not want to make a special trip to a truck scale or gravel pit or feed supply to get your individual tire loads you can at least stop at a truck stop on the Interstate on your next trip to get a reference number for each axle.
HERE is a worksheet to allow you to calculate individual position weights.
and HERE is a Youtube video on how to weigh on a truck scale.

Trailer tire inflation:
To lower the Interply Shear (force trying to create a tread separation) You should run AS A MINIMUM the inflation required to support 110% of the MEASURED load on the most loaded tire. Better yet run the tire sidewall inflation number. You can learn more from THIS Google search or go to my blog and read up more than you ever really want to know about the tire mechanics involved in the tire construction.

Hope this helps.

Friday, October 18, 2019

Run-Flat tire device questions.

Starting in 1972 I worked on a number of different "Advance Tire" projects Some were looking at an "aftermarket" device that could be placed inside a tire to offer some "Run-Flat" capability. Foam Aluminum and foam Urithane were used. These worked but were too heavy and expensive for general use by the trucking industry and they were not willing to pay the penalty of the original cost and the loss of load capacity for the truck. Visually they would resemble the Rettroband. Here is a picture of a similar device.  Having watched the Rettroband video it appears they have a unique method of "attaching" the ring which was one of the areas we did not finalize.
I was also the project leader on the original "Run-flat" tires applied to the people mover train at the then-new DFW airport. This approach involved filling the air chamber with a rubber foam material (not urethane but flexible rubber)  I believe that this is the approach used on some military vehicles today.

This is not some secret "magic" stuff that is being kept from public use by the military as some have suggested and it is not some "Area 51" SiFi material. Just rubber with a blowing agent. If you were willing to spend maybe $500 - $1,000 a tire, limit speed to an average speed of 25 - 30 mph and do a complete redesign of your front suspension to handle the 150 to 200-pound increase in tire assy weight, I believe you can have this on your vehicle. Oh, you also would need to be willing to scrap the wheels when your tire wears out and you can not dismount a foam-filled tire.  Other "run-flat" military systems use a flat base multi-piece wheel with an internal ring along the lines seen here.
Note how the flat base multipiece wheels are assembled.

Other approaches involved going from 22.5 wheels to 26.5 diameter wheel while retaining the same OD, width and load capacity as the original 11-22.5. We even had about 600 special wheels manufactured and we applied these wheels and tires to hundreds of HD trucks. I posted info on my tire blog about these tires. The problem with these tires is they needed new wheels. While these tires provided significant improvements in vehicle control with a sudden loss of air on the front. the trucking industry did not feel the improved safety outweighed the increased cost of new wheels.

The Tyron system does not appear to offer any support of the tire tread or feature to limit the "drop" which IMO is an important feature of limiting the degradation or loss of vehicle control due to "blowout" but is intended as I understand it to prevent the flat tire from being dislodged from the wheel.

Friday, October 11, 2019

You Tube videos on RV tires.

Earlier this summer I had the opportunity to be interviewed about RV tires on the RV Show USA with Alan Warren.

Take a look.

The second part focused on "China Bombs"

Friday, October 4, 2019

My tire says "Regroovable" What does that mean?

"Tireman9; I directed a question to you and did not get an answer?
My Goodyear tires say they are re-groovable. Do you approve of this and who does it? I am located in Indiana. TIA
RVForum writer"

I remember the question and thought I answered but can't locate the original question.

Anyhow.  "Regroovable" is on many HD truck tires. It means the tire was designed and made with extra thick rubber under the tread pattern. Many truck tire shops can cut a partial pattern into the remaining rubber after the tire has been significantly worn. There are guidelines provided by the tire companies on the depth etc.

HERE is a short video. You may notice that in the example the tire is a "Lug" or heavy Traction" tire as used on the rear of units such as Dump trucks.

Regrooving only provides more tire wear miles and will not extend the long term life of a tire based simply on age.

You would still be constrained by the published guidelines of 10 years max no matter what the visual inspection indicates and the act or "regrooving" the tread paternwill do nothnig to improve a tire's durability.

A downside of a tire being "Regroovable" is that the heavy, thick tread will almost certainly give you worse fuel economy as most of the tires e"energy" is consumed n the tread regon

Friday, September 20, 2019

Two front tire "Blowouts" in one day

There was a thread started by the owner of a Class-A motorhome who suffered two front-end "blowouts" on the same day. There was not a lot of data provided such as actula load on each front tire or the tire age or even when the last tire inspection was completed. But here is one of the replies in the thread:
 "The reason that your coach is equipped with a heavier axle and bigger tires is exactly that the axle and tires on the earlier model Aspires were too close to what the coach was carrying. The close limits on the Aspire as well as the tire choice on OEM tires have been a well-known concern for years and many Aspire, owners, that frequent this forum have shifted their tires to tires with higher weight tolerances and inflation load-carrying specs and overall better safety record.

My 15 Anthem was similar. With me fully loaded for travel (which was still well below the coach's maximum rated weight, and tanks all loaded and us sitting in our seats, I was also overloaded on my front axle by 140# which was deemed acceptable. It was that way the whole time we owned her. A whole lot of weight is borne by these front axles on coaches this big and heavy..... within tolerances and specs but close."

I can't address the accuracy of Gary's comments on the Aspire or Anthem motorhomes but I have heard of other cases where the OE tires and even front axle in one case, was in overload when the RV was shipped from the MFG. added the following:
Individual tires don't care about the load on the other tires on a coach or the average load on all the tires. Only on the load on that individual tire. This is why "4 corner weights" is strongly recommended for all RVs.

GAWR, not GVWR is what is important for each axle BUT that is assuming a perfect 50/50% side to side split in load which is almost never the case. Some coaches have been fount to be unbalanced by 500# to over 1,000# yet still close to GAWR.
Also having a reasonable "Reserve Load" is very desirable, especially in the more critical front position. A reserve load (tire capacity minus the measured load on that tire) of at least 5% with 15% being a good goal may require changing the amount of "stuff" you carry or moving "stuff" around or even getting higher rated tires.

You can also stagger tire replacement if you have the same size tires in all positions. I cover how to do that in my post on spreading out the replacement cycle.  My post has a 1-year cycle but you could easily change that to 2 years and never have tires over two years old on the front axle.


Friday, September 13, 2019

Truing tires. Is the tire properly mounted? Is the tire even to cause of vibration?

Had a question from "Fred" on "Truing Tires"
On a different subject, on the Escapee's forum, there was a conversation about tires, and someone mentioned truing new tires. IMO, truing of new tires today only covers up poor mounting procedure, vs 40-60 years ago when tire construction was not as advanced. What are your thoughts on this?

 First, let's be sure everyone knows what we are talking about.
The process of "Truing " a tire involves shaving part of the tread rubber off to make the mounted tire more round. HERE is a YouTube video showing the process.
I tend to agree with "Fred" that most out-of-round problems can be traced to a tire not being properly mounted and seated on the rim. It is also possible that the wheel itself may not have been properly mounted on the hub or it is even possible for the wheel itself to not be round.
 If you have a vibration problem you first need to ask "What has changed?" Did you just get new tires? Are the tires the same but the wheels were off the vehicle for something like a brake job? Have you been driving on especially rough roads with many large potholes? This is a "new to you" vehicle and you have no history with the tires and wheels on this vehicle. On some vehicles "Heat Set Flat-Spot" may be the cause. This happens when tires have been run, getting hot and you just stop and park the vehicle. Sometimes leaving the vehicle parked for weeks or months can also allow the tire to get a flat spot which could take a couple of hours running to work the flat spot out. High-Performance Passenger tires are more susceptible to this problem than large 22.5" size radials but even 22.5 tires can develop a flat spot.

The problem of vibration can usually be traced to either out of balance or the tire/wheel assembly being "Out-Of-round".
If you have vibration on a new tire, I would first confirm it was balanced. Next, I would measure the assembly on the vehicle and confirm it is in-tolerance. This usually means less than 0.030" radial runout goal with 0.125" the upper limit.
If you are exceeding the above, the next step would be to try and confirm which component is not "round". Ideally, you would confirm the wheel, with no tire mounted, was below the limit. If the wheel is "round" when measured on a mounting machine then we would need to confirm it is round when bolted to the hub. Some wheels are "Hub-Centric" and others are "Lug-Centric". Hub centric means the wheel centers on the ledge of the hub on the brake drum. Lug centric means it centers on the bolts holding the wheel to the hub. A lug-centric wheel can easily get "off-center" if one lug nut is fully tightened before the other lug nuts are snugged up. There are patterns for the sequence and steps of tightening lug nuts depending on the number of lug nuts. Here is the sequence as published by Chilton, a publisher of numerous automotive repair manuals.

 Image result for 10 lug nut tightening sequence
 In addition to the above sequence, it is advisable to tighten the nuts in three steps of 1/3rd of the torque level. Example: if your torque spec was 90 Ft-Lbs you would first do all the nuts to 30 ft-lbs then again following the sequence tighten to 60 Ft-Lbs. The finally to the 90 Ft lb spec, again following the pattern
If the pattern and amount of torque are not followed it is easy to end up with a round tire & wheel assembly to be mounted off-center to the hub which results in an out of the round situation and unacceptable vibration.

Before I resorted to shaving a new tire I would measure the out of round. If you have confirmed all the above yet still have vibration on new tires, I would work with the tire dealer to confirm there is nothing in the individual tire that might contribute to some vibration by simply switching tires around or trying a different set of tires.
In all probability, by now you would have found and fixed the cause of the vibration.

Friday, September 6, 2019

Are Hankook tires any good?

Read this question from an owner of a large RV

"Looking to replace the tires on my 33 MH. Was thinking about Hankook as I only put 3500-5000 miles per year on them, But I have seen a lot of negative reviews fo Hankook tires on cars but not seeing much on RV tires. Any suggestion?

My answer

While I can't address negative reports on some applications for some brands I do know that I can find negative posts on just about every brand tire I ever heard of.
A couple of points

No company that makes Passenger, Light Truck and Heavy truck (RV) tires make them with the same materials or on the same building machines. I doubt that you think that winning the Indy 500 means you can expect the same materials or process to be used in your 365/70R22.5 LR-J tire.
I have a couple of posts on my blog with links to videos of tire manufacturing process new and old, showing just how different the manufacturing process can be. The raw materials are different and the internal QA testing is different, so I don't feel it is reasonable to use a broad brush of "negative reviews" from some individuals to consider all the tires a company makes must also be bad especially given the well-documented cases of poor or non-existant tire maintenance for so many vehicle owners.

When people ask me for recommendations for tires I offer a couple of suggestions:
1. You can check with NHTSA and check for current recalls for the brand and type tire you are considering.
2. Visit the company web site and see if you can locate dealers or stores in the states you travel to. If there are hundreds of stores then it would follow that it should be easier to get service and that millions of consumers must be happy with the products that the company makes. When doing this check confirm that you have visited the appropriate company web site. Some companies separate passenger and Heavy Truck dealers and you should not expect to be able to get service for your 22.5" tires at a passenger tire dealer
3. Don't use purchase price as your primary yardstick
Things to think about. What was the complaint in the negative review? price? Service at a particular store? The tires didn't deliver 70,000 miles wear? The fact that the tire suffered a puncture? Maybe even a complaint about a tire failure but the failure was traced to a valve core leak. I have even heard some complaints about the style of lettering on a tire sidewall.

Bottom line I know of no reason to not include Hankook brand on your shortlist.


Friday, August 30, 2019

When you "upgrade" the Load Range, what inflation to run on trailer?

Another question from RV trailer owner "I am replacing the tires on my small (12-14 ft, depending on how you measure) travel trailer. I plan to buy Good Year Endurance ST205/75R14, load range D to replace the brand X Chinese ST205/75R14, load range C.

Vehicle manufacturer says to inflate to 50 psi. Sidewall on existing tires have 50 psi listed as max.

The replacement Good Year tires have max of 65 psi on the sidewall.

I see that the opening post on this thread says to use the sidewall pressure. But I have always gone with the vehicle maker's suggestions which are often lower than the max tire rating. For example, my F-250 wants 65 psi in front and 80 in the rear.

Do I use the 65 max on the tire or with the vehicle manufacturer's 50 psi?"
So I said:   Simple question but I can make the answer complex.

The MINIMUM inflation you need to run is what the Load Inflation tables show for the actual measured load on your tires.
Lacking the actual scale reading, we need to look at your RV certification label that identifies the MINIMUM inflation your trailer mfg recommends. This is based on the DOT requirement that the tires be capable of supporting the GAWR load as shown on the label.

RVIA (Recriational Vehicle Industry Association) in 2017 started to require a 10% Reserve Load (Load capability more than the GAWR minimum).

As a tire engineer, I come at the topic of trying to provide the best conditions to allow the tires to run the longest. As I cover in my this blog post, trailers place extreme shear forces that are 24% greater than similar forces experienced on motorhomes. This, IMO is the primary reason for tire life in trailer application being less than on motorhomes.
Also, you need to remember and understand that it is the air pressure, not the tire sidewall that supports the load. If you run the inflation used in LR-C tire in a LR-D tire, you will have no increase in load capacity so will gain nothing.

Having said all this I would suggest you run at least the certification label +10%.  If you can run label +20% that should result in better durability.

See that wasn't too painful.


Friday, August 23, 2019

Why are ST tires better than LT type?

Following some posts on an Airstream forum of tire inflation and type tires. Some are complaining about rivets "popping" when they increase tire pressure. Many questions in the thread and some confusing replies.  I thought some readers might find this information interesting.

Some general observations and comments.
On this RV forum, there are two Tire engineers with significant Forensic Tire Inspection knowledge, myself "Tireman9" and "Capri-Racer" Our focus is on getting a better tire life and seeing fewer structural tire failures.
Out there, I would guess there is a pop rivet expert who would ask why the size, number or type of rivet being used is failing at a high rate on Airstream trailers. Airplanes are riveted together but I don't hear about "poped" rivets in that application, so maybe there is room for some improvement in the rivets called for.

Very few RV owners know the actual load on their tires. Simply dividing the scale weight by two or 4 (the number of tires on the RV) doesn't provide the correct answer, as it is easy to have one tire position to be hundreds of pounds heavier than another and they only respond to the actual load on that tire and not some mathematical average.

Also, I don't know the loaded weight of each year/size/model TT so can't provide an informed estimate on the inflation that TT should run without knowing the actual measured load on each of your tires.
I do know that having a MINIMUM of 10% Reserve Load (tire capacity - actual load) is a new requirement (2017) from RVIA (Recreational Vehicle Industry Association). DOT has no margin requirement ( Zero%). Capri and I are on record of suggesting at least 15% margin. The Interply Shear numbers would suggest that TT need to have a reserve closer to 25% if you want tire life more like a Motorhome gets (5 - 7 years).

Since it is the air pressure that supports the load and not the tire, simply going up in Load Range but not changing the inflation will in all probability not gain you anything in actual load capacity.

The pressure on the tire sidewall isn't really the "Maximum" you can safely use but is the MINIMUM inflation needed to support the MAXIMUM load that is marked on your tire sidewall. Personally, I do wish the wording on tires was more technically accurate but I can only guess that the lawyers and bureaucrats decided to use "max" in relation to the pressure for some reason.

Here is a question I wish someone could answer. Why are ST tires rated to support 10% to 20% more load than the same size LT tire? In the past, the reason was that ST tires were only rated to 65 mph to compensate for the increased load. Now ST and LT tires have almost the same speed rating but ST still carry the extra load capacity? If tire companies could all simply improve their ST tire Speed Symbol, almost overnight in 2017, why don't they use the same "magic" tire construction to increase the load rating of their LT type tires?



Friday, August 16, 2019

Is it true a pick-up tire is better than a trailer tire?

That's a question I received the other day. Here is my reply.

Well, I'm not sure, is Spaghetti better than Lasagna?

Ok seriously. No good way to answer your question as an LT tire is intended for passenger-carrying vehicles while ST type tires are specifically designed for trailers not carrying any passengers.

The Load formula for these two different type tires is different, just as the formula for P-type or passenger car type tires are different. ST type tires are rated for about 15% greater load capacity, depending on the specific size, but with a max speed of 65 mph.  So if you never exceed 65 mph, ST type is "better" as they are rated for higher load.


DOT testing for LT type tires is more substantial (more difficult) and has more requirements than the requirements for ST type tires. So if you believe that being able to pass more difficult tests indicates a "better" tire and you want better durability then LT tires are better.

Now if you want to compare two different size or different Load Range tires but the same load capacity then IMO most LT tires are probably better than most ST type tires based on their ability to pass the more difficult DOT tests which are based on load. 


What if you consider lower-cost your "measure" when comparing tires you might find that many ST type tires have a lower price than many LT type tires.


Thursday, August 8, 2019

How old is too old ?

For RV application this is a tough question, because "It Depends".

Primary factors that affect the answer include 1. Type of RV -Motorhome, tandem axle trailer or single axle trailer.   2.Cumulative temperature i.e. How much time with tires below 60F  Below 70F,  below 80F  below 90F  Above 90F, Above 100F, etc up to Above 140F     3. Actual Reserve Load   4  If a trailer, how many times you backed into a parking spot  5. Do you use white tire covers or is the RV parked in full shade?

Ya, a lot to consider but each of the above items can shorten tire "life".  Would it be possible to construct a formula or spreadsheet with answers to the above to calculate the answer?  Yes but I doubt it would be worth the effort as the life of one brand or size would probably end up with different detailed factors. So let's just consider some of the items I listed so you may gain a better understanding of "tire life"

#1 Type of RV. This is where "Interply Shear" (a force that is trying to tear the belts off the body of a radial tire) Based on computer simulation this shear or tearing force is 20% or greater in tires applied to multi-axle trailers than if the same tire was applied to a motorhome, even with identical weight.  For those that care there are a number of posts on IPS on my blog if you really want to understand the background and how this force affects tires.

#2 Heat. This is the number one "killer" of tires if we set aside the obvious failures due to loss of air pressure. In fact, even the loss of air pressure results in excess heat that can lead to rubber reversion or even melting of body cord which leads to many "Blowouts".  Heat damage is cumulative and has a MAJOR effect on tire life. The reason for this is that rubber is always "curing". In technical terms, this means the molecules of Carbon and Sulfer are continuously linking, although at a slower rate when relatively cool 70F and below and the rate of chemical reaction doubles with each increase in temperature of 18F. I have a number of links to Scientific papers on the chemistry of tire curing in THIS post. It is also important to understand that the hottest area of a tire can not be measured with a heat "gun" or even with TPMS. Here is a graphic showing the relative temperature in different areas of a tire. The internal red area can be 20°F hotter than the rubber just 3/8" away and the range of temperatures in this example is 80°F so measuring at the correct location is critical as well as very difficult as it takes specialized needle probes.
 Also, this is the location of the highest level of Interply Shear.

#3 Reserve Load  This is the difference between a tire's load capacity at the cold inflation number in the tables vs the actual measured load on a tire.  Greater reserve load means cooler running temperature. See #2 above

#4 Backing into a parking space. This is something few think about but in extreme cases, the interply shear might get to 100% higher in a tandem axle trailer when doing a tight turn into a parking space. This high tearing force can initiate cracks in the rubber which can just grow and they never "heal) which can lead to belt separation many hundreds or thousands of miles later.

#5 Tire Covers.  See my post on using white tire covers.  Yes, this simply goes back to cumulative heat. See #2 above.

Long term readers of my may remember my post on how to maximize tire life.

One thing that is true is that Michelin and some other tire companies have set 10 years at the maximum life of a tire no matter what it looks like. This does not mean that no tire will fail due to "age" or the cumulative effects of the conditions I have outlined above. All of these conditions simply are shortening tire life from 10 years down to maybe as little as one or two years in extreme cases.


Friday, August 2, 2019

What's a good Tire Pressure Monitor System for a Class-A?

Had this question asked on an RV forum I monitor. Thought I would share my answer.
While I don't have a Class-A, other than the length, I'm not sure if any one system is significantly better than another. As long as the system you buy can handle the total number of tires on your coach + toad AND is rated for your tire pressure. Warranty length and service may be the only meaningful difference between some units.
I have done what I think is the only direct real-life comparison of internal vs external system back in 2018 and published the results on my blog.
But some general observations and comments.
IMO User-replaceable batteries are a plus. You can confirm the battery P/N before purchase and check at a grocery store or at Home Depot or Lowes for both price & availability but most are under $2 each and last 1 to 2 years depending on use.  I have found that after 8 to 18 months use, low battery power may contribute to the dropped signal. My solution is to mark the install month year date with Sharpie.
I do like a system with long (Lifetime?) warranty and one that actually has the dealer/distributor attend RV conventions as that means they have people that are not just selling "widgets" on Amazon and probably have a telephone, email, and website.
RE: Repeater. I have listened to the "sales-pitch" from a number of different vendors at FMCA Convention and most will ask about the type & length of coach and offer suggestion to get a repeater or not but I also note that some will offer to send a repeater for just the cost of the repeater if you discover you need one later. Others just include a repeater with all sales just ask and see what they say or offer.
Alarms going off. I have a blog post on how I set my TPMS and haven't had any false alarms with the TireTraker system I purchased in 2009 (I did upgrade to the TT500 in 2018 after I killed the original TT400 monitor by connecting the wrong charger to it. My error not TT)
I have found I do not need a power cord to the monitor on the dash as a single overnight charge is good for weeks of daytime use.
I do shut off the monitor each evening. In the morning I turn it on again and by the time I am done with my coffee all 6 sensors have sent in the baseline pressure so I get a fresh "cold" pressure reading just to keep an eye on things. Do not be confused with the time to establish a signal. As far as I know, sensors only send a signal once every 8 to 15 minutes to conserve battery life. They also will send a Low-Pressure warning within 2 to 4 seconds. Read the literature or ask the dealer to learn what your system timing is.
Maintenance:  I do run a "test" every year to confirm the sensors are still reporting air loss in the first few seconds. The post also covers spare parts I keep on hand.


Friday, July 26, 2019

Max Load - Max Inflation & Cold Inflation confusion continues

From an RV Forum "My understanding is that the number on the side of the tire is not a recommendation. Rather it is the maximum cold temperature that the tire is rated for. You should never run above that number. Without actual weights, I would run the recommendation from the motorhome manufacturer on the placard near the driver's seat, or a little higher, but never over the sidewall number."

The information on the tire sidewall is a statement of the maximum load capacity and the cold inflation required to provide that load capacity.

Different tires have the word "max" placed in different parts of the phrase which leads to the confusion.

Here is a post on passenger tires.

Here is a post on when the Minimum inflation is the Maximum.

Note: A a statement of Max Load "At" stated inflation such as "Max load 3,000 lbs at 80 psi" is leaving off the implied "minimum" before the 80 psi.

Also introducing the word "cold" seems to confuse some.

Maybe this will help:

Tire inflation should only be set when the tire is at ambient temperature and has not been warmed by being in sunlight or driven on for the prior two hours.

A tire may be loaded to the number of pounds stated on the sidewall, only when the tire has been inflated, when cold, to the stated pressure on the tire sidewall.

The problem is that these phrases don't fit in the same place as current "Max Load 3,000 lbs at Cold inflation 80 psi"

Friday, July 19, 2019

Lug nut torque. A critical SAFETY item.

Those that have read their owner's manual, may recall seeing a mention of the need to check the lug nut torque. In this case, we are talking about how "tight" the nuts should be to ensure the wheels stay on our vehicles. Others may have a warning label on the inside of their RV. This is from my Class-C Coachmen.

Note: Class-A and RV with 10 bolt wheels probably require a service truck and torque in the 450 Ft Lb range, so this info may not apply to you as you will need significantly different tools.

Here is a video showing what can happen if lug nuts are over-tightened or are lose.

First the simple answer:
- Look up the specification in the Owner's Manual.

Here is a sample page from Heartland RV. Note they tell you how often to check and how tight to make the lug ut and even the pattern for the sequence of tightening the lug-nuts as seen here:

Image result for 10 lug nut tightening sequence- With your torque wrench follow the instructions for both frequencies and how tight the lug nut should be.

- What to do if you don't know what a torque wrench is? Watch this video

- What to do if you don't own a torque wrench?
There are a bunch of videos that compare wrenches HERE   But you can get an OK wrench like THIS for $20  or a better quality one like this for $100.   You do not need to buy the most expensive wrench as hopefully you will be only using the wrench a couple times after a tire or wheel was changed on your RV. Or maybe a couple times a year per your Owner's Manual instruction  For infrequent use I have found Harbor Freight non-digital adequate. Just be sure to get a 1/2" as your lug nut torque spec is probably in the 75 to 130 Ft-Lb range. Don't get a wrench that is right at your spec as it will probably have a short life and may not be accurate at 100% of its rating.

Now some background:
Do not lubricate the stud or lug nut with oil. This can affect the torque reading and could lead to stripped threads in lug nuts ($) or broken wheel studs ($$$).

This web site gives a technical background on why not to lubricate lug nuts.

Some Technical Info for those that want to know more:

Torquing a bolt is to get a certain amount of stretch out of the bolt. If torquing a bolt to 80 Ft-Lib, it is technically more accurate to say "When you torque this bolt to 80 ft-lbs, it will cause it to stretch by .0030 inches". In critical applications such as race engines, many engine builders use certified bolts and actually measure the stretch of the bolts rather than using a torque wrench.

Think of the bolt like a spring. When you torque it, you're stretching it so that it exerts force on what you're holding together. This video goes deep into bolt stretch vs torque.

When I was driving my race car, confirming the torque of the lug nuts was MANDATORY before each track session. With this as a standard practice, I never had a wheel come lose in 30 years of racing.


Friday, July 12, 2019

Why inflate Motorhome tires differently than Trailer tires?

Found the following in a thread on an RV owner's forum. This came after there were comments about the advantages of inflating trailer tires to the tire sidewall inflation number but inflating Motorhome tires based on the measured load on the tires.

 "Such a hard concept for most to understand."

As an actual tire design engineer, not just someone that has used a lot of tires or bought or sold a lot of tires, I feel I might have a slightly better understanding of the science behind why tires fail.
I try and make the information easy to understand but I find that many simply refuse to accept the fact that my 40 years experience that includes thousands of failed tire "autopsies" might qualify me to give sound advice.
If you simply look at the experience of three groups of tire users. Excluding punctures or pothold impact breaks.
1. Regular motor vehicles. People get about 40 to 50,000 miles before the tires "wear out"  less than 1% experience tire failures.
2. Class-A and Class-C motorhome users. Many only drive 5 to 8,000 miles a year. It is recommended that starting at 5 years of age, tires be professionally inspected. This does not mean a simple walk around to look at the tread depth but close inspection with good lighting. Maybe even using a pit to allow the inner sidewalls to be inspected. Annual ispections thereafter are recommended and replacement at 10 year tire age "no matter how good a tire looks" This group also has a low structural failure rate not tracable to air leak or impact.

3. RV Trailer users "Towables". Based on numerous reports of higher structural failures i.e. belt/tread separations, and some strange patterns left in lose gravel where a trailer was turned 180 degrees I had some computer simulations run and the numbers provided an explination for the "why" towables have a mush worse structural failure rate. The forces inside the tire structure are significantly higher (+24%) in trailer application (i.e. towables) than in motor vehicle applications This force is identified as Interply Shear and it shows up as trying to separate the top steel belt from the bottom steel belt in radial tires.

While it would be possible for RV Trailer companies to make design changes to trailer suspension to allow for "passive steering" as seen on large cement trucks with a tag axle, I doubt they would go to the expense simply to extend tire life.

While lowering the actual load on a tire in trailer service can lower the Interply Shear force I doubt that it is possible to lower the load by 40 to 50%. One thing trailer owners can do to lower this force is to increase the cold inflation to the tire sidewall "max" Sorry to say you can not reduce the Interply Shear to zero as this is the nature of radial tires.

Friday, July 5, 2019

Modern radial tire assembly -Worldwide

UPDATED with all new videos  6-12-20

A very good 4:47 min animated video fromU.S. Tire Manufacturers Association

on how modern radials tires are "built,"  The video says "Passenger tire" but the process is essentially identical for any radial tire such as Passenger, LT or ST type.  Heavy Truck or Class-A RV are similar but will probably have three of 4 belt ply and of course thicker and stronger components.

THIS video shows actual tires being made and offers a bit more detail.

A longer and more detailed video from Pirelli that focuses on high-performance tires but the steps as you can see are very similar,

A video from 1934 shows that even then the various steps were similar just not as well-controlled and managed with a lot more manual labor. Tires in this video are Bias, not radial.

Finally a modern Truck tire (Class-A RV size) from Bridgestone. might the best for RV owners to watch.

There isn't a tire plant worker in the world (China, Europe, or the US) that would not recognize what the equipment is doing in any of these videos

Yes, the machines are painted different colors and the robotic handling of the tires is done with different equipment but the end result is almost identical.

This uniformity in the process is why, I have so much difficulty in accepting the idea that because a tire is built in one country, it is automatically more likely to fail than when it is made in another country.

Friday, June 28, 2019

Critical tire temperature ?

Received another question
Hi Roger, I just read your article on sidewall strength and “blowouts”. You mentioned that if the temperature rises too high the sidewall cords may melt. I have a 2017 Winnebago Grand Tour with a built in TPMS system with pressure and temperature sensors. Most RVers know (or should know) to keep their tires at the proper inflation level. The one thing I haven’t seen addressed is tire/air pressure temperature. As I drive down the road I can watch the pressure rise with a corresponding temperature increase. Is there a critical temperature to watch out for exclusive of tire pressure? If so, I’m sure it would be different for each make/model and tire size. Do manufacturers publish any specific data for their tires (i.e. a critical do not exceed temperature)?
Thanks for all you do to keep us in the loop.


Ken, If you check out the posts on my blog you will find numerous posts on tire temperature and pressure.

RE Critical temp.  For short term (MInutes or seconds) I would consider structural temperatures in the 205 - 230F to be critical. Size, brand or design, doesn't make much difference. The problem is there is no way to measure the temperature as the location of the hottest location is at the edges of the radial belts. In racing, like at Indy we use a needle probe and stick this into the tire about 1/4 to 3/8" deep. External surface temperatures are much cooler because of external air moving over the surface. With rubber being such a good insulator the heat does not travel to the surface fast enough (minutes) relative to the ability of the temperature to rise (seconds) at the critical location we see it possible to have internal rubber failure before the surface temperature gets to a critical point.
I think you can understand that the rubber can get softer with an increase in temperature. As it gets softer, it stretches more, as it stretches more it gets hotter, etc. Up to about 210F, this increased softness can be managed with construction and thickness design changes but each of those changes can result in some other property getting worse. Also, that 210F point, changes with time and temperature history. Tire design is a balancing act and a series of trade-offs. One thing that happens with a loss of strength and increase bending is the potential for tearing of the rubber at the molecular level which can result ultimately with the tearing to grow to the width of the belts which in turn results in a belt separation.


The key thing to understand is that temperature damage is cumulative and the chemical reaction that occurs can eventually result in a loss of elasticity at higher temperatures so the rubber tears which leads to a separation. The rate of these changes can itself change over time and the rate is also affected by the temperature.
Even for a single rubber compound, there is no exact temperature for it to "fail". The physical properties of rubber changes with temperature but here there is no exact point at which the strength goes from 100% to zero.

TPMS gives an approximate temperature of the air inside a tire which is also lower than the critical temperature. Most TPMS have a high-temperature warning set to 158F and if you see that reading then you do not have enough pressure for the load you have or are driving too fast. This does not mean you can lower pressure till you see a reading of 158 as you are still doing damage and "consuming" the finite life of the rubber in a tire.

Read my blog, Learn the actual load (when the RV is its heaviest) for each tire position (4 corner weights) Consult the tables, Learn the MINIMUM inflation pressure, add a +10% inflation margin to learn your "cold set pressure" for each axle based on the heaviest axle end, Adjust your TPMS low pressure level to never be lower than the minimum. The go and enjoy your RV

Friday, June 21, 2019

Tire sidewall "strength". What does that mean?

I note that on many RV forum posts on the topic of tire "Blowouts," there many times are posts on the "Strength" of the tire sidewall. Before I start, it's important that we have a shared definition of a few words.
"Blowout" is simply a statement that a tire failed catastrophically. It does not mean it simply exploded as if it were a bomb.

Belt or Tread Separation is the detachment of the belts and or tread in a radial tire. This can lead to a rapid loss of air which can make a loud noise, surprising the driver and leading to the idea that there was an explosion or "Blowout". But not all tires that have belt separations end up with a rapid loss of air. Here is an example of a tire with tread & top belt detached from the rest of the tire. It is shiny as I sprayed water on the tire while inflated on a wheel to inspect for punctures or leaks as I had suspected the tire had been run with low inflation. I "redacted" identifying marks as that information is not important for this discussion.

Sidewall Failure for this discussion means a failure of the tire sidewall not related to a sidewall cut or impact. many times when a tire loses air but is still being driven at highway speeds, the body cord or "body ply" material can fail due to excessive heat.  A more technically accurate term used by tire engineers would be "RLOF" which stands for Run Low Sidewall Flex Failure. Most Passenger, Light Truck and ST type tires made today use Polyester cords the sidewall ply.  With excessive flexing and bending from low inflation, the cord can overheat.

If the temperature gets high enough (300°F to 350°F) the cord can lose half its strength and high temperatures can result in the cord melting just as you have seen when you melt the end of a piece of Nylon or Polyester rope with a match.
 Here is what melted tire cord looks like.

I have shown this condition in a few posts, but probably the one with the best example is my post "Blowout- Real Life Example"

So why does this engineering stuff make a difference? You still had a "Blowout," and are not happy. Probably want to blame someone and the tire company is an easy target. BUT as I have said before if you do not know the real reason for a tire failure you might not prevent another failure from happening.

Imagine you had an RLOF but did not bother to try and learn why the tire was low on air. Puncture, cut, leaking valve, leaking valve core, cracked wheel are all "suspects" and just replacing the tires on your RV with a different brand will not prevent another "Blowout".

So this leaves the question of Sidewall Strength. DOT has a specific test to confirm a minimum "strength" for tires. The test procedure. involves forcing a 34 inch diameter steel rod with a hemispherical end perpendicularly into the tread as near to the centerline as possible,  at the rate of  2 inches per minute. This is repeated 5 locations around the tire and there are published minimum energy requirements (inch-pounds force) that tires must exhibit. These minimums are based on the tire size, type, and Load Range.

Now you may ask: How does the sidewall material strength come into play? Well, the sidewall material runs under the belt material so is part of the total strength requirement. Tire companies also have their own "Burst" test requirements which involve mounting a tire on a special test wheel and increasing the pressure till the tread or sidewall or the bead fails. They use special wheels as most tires are stronger than regular production wheels. The minimum pressure is not published but in most cases, it is in excess of three times the inflation number molded on a tire sidewall. and in some cases, I have seen tires exceed six times the inflation number on the sidewall.

Tire Design engineers have a wide choice of sidewall ply material to choose from. Different types of cord, different sizes and even different amounts or cords per inch circumference can be selected as the engineer works toward the final design specification. Simply claiming that "Our tires have larger and stronger cord" while true doesn't address the question of how much of that cord is used in the tire.

Bottom Line. I hope you now understand how simply claiming the tire sidewall wasn't strong enough will not help you solve your tire failure issue.