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Wednesday, December 16, 2015

Changing wheels? There are some important dimensions and specifications to do this safely.

I recently read a thread on an RV trailer forum where some were considering changing the wheel diameter so they could get an increased selection of tire brands, sizes and load capacity to address tire failures. One person said
"I am looking at some nice 16" wheel tire combos but I'm wondering if they'll fit my trailer. They came off a different tow vehicle. Do I need to expect to swap out size up the hub where the wheel bolts are?"

I had some concerns as if someone is swapping wheels there are a number of dimensions and "fit" issues that need to be considered if you want a safe vehicle.

Wheel "offset" controls the location of the tire toward or away from the center of the vehicle. Tire Rack has a good tech page with drawings and definitions "The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types (measured in millimeters).*"

Center bore may be critical as some wheels are "hub centric" which means the center of rotation is controlled by the fit of the wheel to the hub. Others are "lug centric" which means the fit of the lug nuts controls the wheel/tire run-out. "The centerbore of a wheel is the machined opening on the back of the wheel that centers the wheel properly on the hub of a vehicle."

Lug nut fit. Most steel wheels have a "cone fit" where the taper of the lug nut fits the taper of the wheel center. Aluminum wheels may have a simple cone fit with a straight taper or a radiused, or “ball” style. The two styles must never be mixed or you can ruin a wheel. The seat profile in the wheel dictates the nut or bolt seat style.  There is also a "mag style" that requires a large flat washer.
While it may be possible to initially use the wrong type nut the results will be a loss of torque and damage to the wheel with the potential of having a wheel come off the vehicle at speed.

Proper lug nut torque is another important number "If the vehicle is on a frame lift, and a helper is able to lock the brakes, the wheel fasteners can be final torqued while on the lift. Otherwise, lower the vehicle to the ground until the tires just begin to load (enough to prevent rotation while torquing). If the vehicle is on the ground with its full weight on the tires, you may be fighting a slight lateral load while final tightening. This is perhaps an arguable point, but final tightening before the suspension is fully loaded helps to obtain a more precise centering of the wheel fastener seats."

Improper mounting and lug nut torque can contribute to what feels like an out of balance tire.

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Monday, November 30, 2015

Don't check your tire air pressure. Really... Stop it.

No, I haven't gone off my rocker as there is some logic behind the title and advice of today's post.

For years the advice has been to check the air in your tires every month and on the RV every morning of every travel day. The primary reason for this decade-old advice has been based on the fact that most RVs have at least one tire in overload or under-inflation or both. Also it is a fact that all tires lose pressure over time and since it is the air pressure that carries the load, not the tire, this makes having sufficient air pressure  more important on RV application than with your regular car.

Why is it more important with your RV?  One major reason is that your car probably has a significant margin in the +12% to +25% range while RVs have more like -5% to +5%, with the plus signifying excess air pressure above the minimum needed to support the load.

But this doesn't explain why I am suggesting you stop checking your air pressure with your hand gauge each morning. The reason for making this surprising suggestion is the fact that the very act of checking your air pressure can, in a small percentage of the times, result in a slow leak through the tire valve core. In some earlier posts on "valves" I showed the sealing surfaces of the valve core and why they can leak. In my experience, valves generally do not develop leaks and are pretty reliable, but the act of checking your air pressure does open the core and there is a possibility that a small piece of grit can be introduced into the core air seal and this grit can cause a slow leak.

Ever wonder why so many people who have a tire sidewall flex failure or "blowout" make the statement, "I just checked the air a couple hours prior to the failure"? Well, this is one of the possible reasons for the small, slow leak.

Now, having made the suggestion that the act of checking your air pressure might possibly cause a tire failure so you might consider not checking your air pressure is only a reasonable suggestion IF you have another method of knowing that your tires are properly inflated. We have that method and it is a Tire Pressure Monitor System.

To me that is the ONLY alternative to checking your air pressure every morning, also every rest stop, also every fuel stop -- and even all those checks will miss a majority of the exposure time when a leak can occur. PLUS, the more times you check your air pressure the greater the opportunity there is for the very act of checking if you have a leak could result in a leak.

If you have a TPMS you really only need to check its accuracy maybe once a season unless you are getting erratic readings and signals. Using a TPMS will not only make life easier in that you don't have to check the tire pressure multiple times a day, but it will also decrease the likelihood of your actions causing an air leak.

If you don't have a TPMS, then you probably should be checking your air pressure frequently -- but just remember that each time you open the valve with your pressure gauge it may not completely seal shut, with a resultant slow leak.

If this post gets you to finally make the decision to get a TPMS you might read my post on Best TPMS to help you make a good purchasing decision.

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Wednesday, November 25, 2015

RV tire load knowledge survey

Here is a quick survey on tire loading and weighing your RV.

I would like to assemble some facts about what people know about their actual tire loading rather than just what they think they know. This will allow me to provide more helpful answers to questions about selecting the proper cold inflation pressure for your RV.

Also I would like to do a few posts on things to consider when contemplating a change in tire size and this data will help provide guidance for those posts.

It will only take about 15 seconds.

Feel free to forward this post to friends with RVs (trailers or motorhomes)

I would really like to have a few hundred responses so the results are more representative of current real life loading rather than numbers based on historical (ten or more year old) data

We will post the results after we get a few hundred replies.

I hope to have a few more polls in the future.

Thank you for participating. The results should be interesting to all of us.

* * *

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Monday, November 16, 2015

When to file a complaint with NHTSA

I have previously strongly suggested that when people have a tire failure they need to file a complaint with NHTSA.

Got this question "Thanks, Tireman. My next question is when is it appropriate to report to the NHTSA? After any flat? Or are there specific indicators?"

Excellent question as we don't need to be "crying wolf"

If we start at the end of the process I think it will help us understand when and why we would want to contribute to the database of tire failures.

I think we can sum up the primary objective for NHTSA as to decrease the number and severity of injury or accident costs due to a failure of an automotive system or component. One way to achieve that goal would be to hold the manufacturer responsible for providing parts that deliver reliable service for normal and expected operating conditions.

One way to hold a manufacturer accountable and maybe "hold their feet to the fire" is to order and require a manufacturer to replace a part that has been found to have an abnormally high failure rate due to either design or manufacturing problems.

Based on data submitted to NHTSA, that agency decides if an investigation should be started. The investigation could be limited to a review of test and manufacturing data or it could involve NHTSA conducting it's own tests.

So what data does NHTSA use to decide it an investigation is justified? There is suppose to be a combination of warranty data from the part manufacturer plus a review of complaints filed by individuals.

This presents a problem for NHTSA. How should they judge consumer complaints when they know that consumers seldom have the technical knowledge to do a proper or thorough evaluation of a product failure?

So the question really is.... Should the tire manufacturer be held responsible for a tire loosing air due to puncture or leaking valve? It may be difficult or nearly impossible for the consumer to do the proper investigation to learn the root cause of the failure.
It is well documented that over half of RVs on the road have one or more tire in an overload and or under inflated condition. Should the tire company be held accountable for an overload or low inflation?

Bottom Line
If you believe the RV company or the tire manufacturer should be held responsible for the tire failure then you probably should file a complaint.
If you take a few minutes you might even decide the failure was not the fault of the tire company but of the RV company that selected a tire with no margin for any loss of air or load variation.
  You still need to provide tire information but in the last case of poor tire selection I would be sure to include statement with actual measured loads and the small reserve load the tire selected provided.

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Wednesday, October 28, 2015

Do you have defective tires? How would you know your tires should be recalled?

While many may suspect their tires are defective because they have had a tire failure, that isn't really a recognized way to know for sure.

US DOT National Highway Traffic Safety Administration does make official determinations on which tires are in a group that might fail. They do issue tire recall orders just as they issue recalls for other suspect defective automotive components.

 A major problem with tires, however, is that according to a brand new report only 1 in 5 tires that are subject to a recall are actually replaced. The suggested primary reason for the low replacement rate is blamed on the low level of tire registrations that are submitted by either vehicle sales outlets or retail tire dealers.

I bet if you think back to the last set of tires you purchased either for your car, truck or RV you were not given a form to complete and mail in to ensure that you would be notified in the event there was a recall issued by NHTSA. This might also apply to the purchase of the tires that came on your RV.
I know that my RV dealer didn't have a clue when I asked them, so I went online and registered them directly with the tire manufacturer.

I have written a number of times on the importance of filing a complaint with NHTSA when you suspect a tire was defective. NHTSA makes a decision on starting an investigation or not, based on complaints received and the seriousness of the consequences of a tire failure. So while you may think the failure is important, unless there are a number of complaints on file there will likely never be an investigation started and with no investigation there is almost certainly not going to be a recall. You need to remember that posting information on an RV forum grousing about tires while sitting around the campfire may make you feel better but it will never result in an investigation or recall or real improvement in the quality of tires applied to RVs.

I have also written a few times here on the importance of registering your tire and these two topics Registering and Recalls are closely related.

If you haven't registered your tires, it is never too late to do so. It doesn't have to be done when new -- it's just easier. Review my posts on the process. You can contact your tire dealer and ask about registration. If they can't or won't help, then I suggest a simple Google of "Tire Registration" will provide the information you need to complete the process.

Of course, a letter to NHTSA, 1200 New Jersey Avenue, SE, West Building, Washington DC 20590   about difficulty you may have in registering your tires might spur them to address the problem outlined in the article.

As Pogo said "We have met the enemy and he is us". When it comes to making the minor effort to file a complaint when you have a tire failure and to ensure you will be notified in the event of a recall by submitting the card with the appropriate information to register your tires, we RV owners as a group certainly have nothing to be proud of.

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Monday, October 19, 2015

How to recognize what might be a better tire to consider buying for your trailer application?

Something to consider when shopping for tires for your trailer:

- Many tires have essentially no warranty, others maybe 12 months and some for years. In my opinion (IMO) the length of time the tire company is willing to stand behind their products is one way to judge the real quality of what they make. Which would you consider a better deal: a hammer with a 30-day warranty for $5, or one with a 10-year warranty for $10?

- Speed rating molded on the tire sidewall to me indicates the manufacturer has made a real effort to exceed the minimum performance requirements from DOT. IMO, tires with a speed symbol are probably better than those without a speed rating.

- Here is a chart to convert the speed symbol letter to a number.

- The speed symbol letter is part of the service description which comes right after the rim diameter in the tire size. Technically, an "LT235/75R15 107/110 Q Load Range D"  is a different tire than an "LT235/75R15 Load Range D" -- with the 107/110 being a load index for dual and single application and the letter Q being the speed symbol.

- I note that most LT tires made today have a speed rating, but when applied to trailer application, some companies say to consider 75 mph as a max.

- I also have recently seen a few ST-type tires now being manufactured with a speed symbol which IMO would make them probably a better choice than tires without a speed symbol.

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Tuesday, October 13, 2015

TPMS don't prevent Blowouts

A reader wrote
"I'm a firm believer in a TPMS, but with that being said, I have a digital gauge. I set my pressure from that and then read from the TPMS I have installed. That has given me the plus or minus of the system which they claim can be plus or minus 1 or 2 PSI. Blowouts seem to happen no matter what precautions you take. I have been to the scales I know that I'm not overweight, I know that I have even wear. I know what my cold PSI is. So what then is a person to do more than that? I do not have control over the manufacture process, so you trust the dealer and data that they supply. So why are trailer tires so much more susceptible to blowouts than tow vehicle tires? A TPMS system cannot predict a sidewall blowout. To me that has to be the cord or construction of the tire itself. It will give me a pressure loss and then you still have to slow and pull off in a safe area that's where the damage occurs. So what are we to do or what do you recommend about that scenario. Thanks for all your help."

By "blowout" I will assume you are talking about "run low flex failure" of the sidewall and not the completely different "belt separation". As such if you can avoid driving at highway speed after the tire has lost significant inflation you can avoid having a run low flex failure, i.e., blowout. So it follows that if you stop driving on a tire after it has lost 30 to 50% of inflation or more, then you will avoid having a sidewall blowout.

I know of no part of the tire manufacturing process that can somehow manage to place "defective" material in a consistent circumferential line only in the upper mid sidewall. Also to my knowledge, no one has been able to identify exactly what the "defect" is that is located at the site of the melting.
Melting of polyester cord can occur no matter the size or number of cords if the sidewall is overstressed (bent) at a high rate. It does, however, take probably about 10 to 20 minutes for the temperature to rise to this level. This type of failure will and has occurred in all brands, so again, what is the exact defect.

In steel body tires we see the same circumferential line with signs of fatigue failure of the steel cords when they are run when significantly underinflated.

The reason trailers have a higher rate of sidewall flex failures than tow vehicles or motorhomes is twofold. First, a tire losing air on a tow vehicle provides the driver the opportunity to feel the change in ride and handling but provides no such tactical feedback if on a trailer. Second is the internal structural stresses that trailer suspension design place on its tires that are not experienced in as high a level in tow vehicle or motorhome applications. Interply shear is about 24% higher in trailer application than in a motorized vehicle.

I suggest you check the Label list on the left side of this blog and review the posts that have a label "Blowout" if you want to learn more.

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Wednesday, October 7, 2015

Quick reminder - Don't get your shorts in a bunch about tire inflation.

Recently was asked why some dealers want to go with the minimum inflation needed to carry the load.

I think the most likely reason for specing the minimum inflation is the belief that customers are more likely to complain about harsh ride even when they are getting better tire life and better MPG. They can feel ride immediately but not see the benefits of inflation to minimum +10% psi at once.

I am also in favor of +10% so you don't find yourself chasing your tail every day by adding 1 or 2 psi when it gets cooler when you find yourself 1 or 2 psi low, or bleeding off 1 or 2 psi when the weather turns warmer.

With +10% it would be easier to discover you are low a couple psi and simply wait till the next fuel stop, where there should be high pressure air available.

For those that don't know how to inflate a warm tire here are the steps:

1. Measure the pressure when the tire is at ambient temperature (not warm from driving or being in sunlight).
2. Note the number of psi you want to add to each tire to get to your goal inflation.
3. When you get to a fuel stop measure the warm pressure.
4. Add the number of psi from #2 to the warm pressure in #3 and add air till you get to at least this new warm pressure goal.

This "rule of thumb" will work for pressure changes of 5 psi or less. If you find you need to add 5 psi there may be something wrong,  i.e., a leak -- and this needs to be investigated ASAP.

Don't get hyper about being 1 or 2 psi off. Remember, if you have a 10% cushion, you are good to go as long as you are within a few psi of your goal.

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Monday, October 5, 2015

What is the optimum tire pressure?

Load inflation tables identify the minimum inflation for a number of specific load placed on the tire.

Tire sidewalls tell you the maximum load capacity for a given tire when inflated to the maximum pressure for that load range in that size tire.

Optimum implies we have common agreement on which performance requirements we feel are most important. Optimum also implies that there is agreement in the inherent trade-offs of the numerous performance characteristics.

If the only performance we are concerned about is load capacity and if we want the maximum capacity possible for the size and load range of a specific tire, then we have a situation where the optimum inflation is the maximum for the load range, which is also the minimum inflation specified in the tables.

If, however, we do not need to support a load that corresponds to the tire's maximum load, then it is possible that other performance criteria may be considered and as a result there will be trade-offs to arrive at a new optimum.

If we are talking about motorhomes, there are normally performance characteristics other than just load capacity. Some might be fuel economy, noise, ride comfort, tread wear, steering response, etc. Inflation pressure will affect each of these characteristics — some positively and some negatively. So clearly the "optimum" depends on the clearly understood and agreed on priority of these and other characteristics.

Bottom line
As a tire engineer I suggest that people select an inflation pressure that will provide at least 15 percent extra load capacity over the heaviest loaded tire on an axle. All tires on an axle should run the same cold inflation. The above will still provide acceptable ride and provide improved durability and fuel economy.

For multi-axle trailers I would consider improved durability, i.e., reduced chance of failure, to be of primary importance. So in this application, the "optimum" inflation pressure would be the pressure on the tire sidewall associated with the maximum load capacity. Even if you are not loaded to the max load you want to lower the "interply shear" forces as much as possible, as trailers induce much higher shear forces than seen in similarly loaded tires would if on a motorhome.

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Monday, September 28, 2015

What readings should I see from my TPMS?

Without knowing the target Cold Inflation Pressure for your personal application, I can only provide some general guidelines to establish the operation of your system.

First off, I recommend that TT with multi axles run a CIP equal to the tire inflation on the side of the tire associated with the max load. This may match the tire placard but you need to read your placard to confirm the numbers.

Motorhomes and other motorized vehicles can use the measured load on the heavier end of each axle to consult published Load & Inflation tables to learn their MINIMUM CIP. For motorized vehicles I suggest a CIP pressure of at least 10% above the minimum number shown in the tables.

Let's assume your CIP is 80 psi, as on most Load Range E tires. One time you need to check your inflation with a good digital gauge and confirm the hand gauge reads 80. Note the tires should be cool and not driven on for at least two hours and not in direct sunlight to get an accurate reading.

Having confirmed the tires are at 80, you can then check your TPMS monitor to see what it is reading. I would not be surprised to see pressure variations of +/- 2 to 4 psi. Remember, TPMS are primarily designed to warn of a loss of pressure, not to be a substitute for hand pressure gauges.

Most TPMS are set to warn when pressure has dropped 15% from the CIP.  I prefer to get a warning before tires get that low so I would set the "base level" of my Tire Traker system at about 107% of the 80 psi on my rear tires to 85 psi. This works out to 72 psi low pressure warning rather than 68 psi low if I went with the original 15% loss number.

Now my TPMS gives both a Rapid and Quick  Early warning when the pressure drops 3 psi from the HOT operating pressure in about 2 to 10 minutes. You will need to learn the details of your early warning settings if you run a different brand TPMS. This early warning is not affected by my CIP or Base Level settings, as it is based on a drop from the actual hot operating pressure.

You can expect to see your HOT pressure to be 10 to 20 psi above your CIP, but this depends on your actual inflation, load, driving speed and road conditions.

You can also expect your operating temperature to be +10 to + 30 above ambient. Since the sensor is external to the tire, it is cooled by the outside air so will never read that actual internal tire temperature. So, in my opinion, if you see +30, you need to slow down and maybe even park for 1/2 hour or so to let the tires cool off. While there are many variables, I would not be surprised to see external TPMS temperature readings to be 10 to 30° cooler that internal tire temperatures so I would consider a +30° reading to be high.

After you drive for a few weeks with your TPMS, you will learn the variation in the readings and should not be concerned about minor variations in the reading.

Hope this helps you understand your TPMS and how to get the information you need from it.

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Sunday, September 20, 2015

"Why do so many RV tires seem to be failing?"

 Well, that may seem to be a reasonable question but in my opinion it is based on what is often inaccurate failure analysis. In reality, tires fail for a relatively small number of Root Cause reasons that can be discovered, but it does require detailed and sometimes exhaustive investigation. By "Root Cause," I mean the initiating feature or condition that eventually led to the failure. Too often people confuse the tire's ending condition with the initiating or "Root Cause" reason for the tire to end up in the condition they are observing.

For the last few years of my 40-year career as a tire engineer, my primary job duty was to investigate failed tires that had conditions that were hard to understand or provided confusing and sometimes contradictory evidence as to the Root Cause for their condition. With that background, I have developed some guiding principles for the most likely reasons for tires to fail.

These are, in no special order:
1. External Damage. These include punctures, cuts, impacts, wheel and valve failures and similar conditions.
2. Run Low Flex Failure. This is best described by the failure of the tire sidewall due to excessive flexing. The flexing is the result of operation when the tire is significantly under-inflated.
3. Belt & Tread Separations. This is when the belts of a radial tire detach from the body or from each other and/or when the tread rubber detaches from the top belt.
4. Manufacturing Defect. For the purpose of this discussion this would be when components of a tire were not manufactured to intended specification.

The "Why" for some of these are obvious, such as the External Damage category.
Others can be further traced to various contributory reasons.

Run Low Flex Failure This is a more accurate description of what some incorrectly call "Blowout". When a tire looses significant inflation air they flex much more that the body cord can tolerate. Excess heat is generated which can, in extreme cases, result in the Polyester actually melting. I showed examples of what this can look link in THIS post. Polyester is used in most Passenger, ST type and LT type tires. Steel body tires are used on most Class-A RVs, the steel can fatigue. I covered "Zipper" failures and steel fatigue in THIS post.

Belt & Tread Separations occur primarily because the rubber around the belt cords or between the belt rubber and the tread rubber isn't strong enough. Now it can be weak for a variety of reasons. Some might be design, some might be manufacturing and some weakening can be caused by cumulative improper service conditions.

Now let's talk about tires made by a reputable company, i.e., one that has tire stores and dealers with physical stores and sells tires that have a warranty of two or more years.
If this tire is subjected to thousands of miles of lower inflation or higher loading or operation at higher speeds or stored is full sunlight it is reasonable to expect the strength of the belt & tread area rubber to loose a good portion of its strength primarily due to the increased operating temperature of the tire. If this tire is in service on a tandem axle trailer then there is also increased Interply Shear which can overload the belt area rubber. The combination of the above may result in a belt or tread separation.

Another possibility is a Manufacturing Defect. These usually occur in small numbers as tires are built in batches so the substitution of the wrong type of rubber may cause tires to fail. It is important to understand that in almost all cases this type of "defect" usually shows up at early life of the tire. It is also very important to understand that unlike some lawyers, engineers deal in facts and logic. Simply having a tire fail is not in it self proof of a defect but all to often that is the position that those in the legal profession seem to jump to. That approach may result in a nice payout to the lawyer but will not result in product improvement as there has been no determination or identification of the actual initiating "defect".

Finally there is the possibility of a design weakness. Now I do not believe that anyone is intentionally designing tires to fail but this sometimes may occur when the performance goals of the manufacturer are limited to meet the bare minimum for strength and durability and the focus is primarily on low cost. There is no absolute way to identify these tires but I do believe there are indicators when looking for tires that are made to a higher standard of quality and durability.
I would consider a tire company reputable if it had a chain of stores across the country. If the tires carry the name of the manufacturer and have a multi-year warranty the longer the better then they probably have higher durability requirements than those established by DOT.

 For ST type tires I would look for tires with a Speed Symbol of "L" (75 mph) or faster. Now a side point about speed. I did a POST a little while ago on the topic and strongly recommend you read it. I do not think I would recommend any tire for general use that does not have a speed rating molded on the sidewall.

I do hope this post will help some to have a better understanding of what can contribute to tire failure and consider what you can do to lower the chances of having such a failure.

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Wednesday, September 2, 2015

What temperature for CIP "cold inflation pressure - Part two

The following is based on a couple posts I made on an RV forum but wanted to share with the rest of my readers

I had posted my comments on the thread from my Aug 25 post on CIP in the hopes of clarifying questions about adjusting inflation for various changes in ambient temperature, but there have been comments that indicate the need for more details when talking about tire temperature so here is a bit more info on the topic.

We really have two different but related temperatures to consider.

One set of temperatures is the external set. This would be the "Ambient" temperature of the air around us and the temperature of the road surface.
 The other and much more important temperature is the temperature of the tire structure.

Now with the correct instruments, it is possible to measure the temperature of the tire structure. This is done at test tracks and at race tracks using a small needle probe that sticks into the tire rubber 1/8" to 1/2" deep depending on the tire type & size and gives a reading the engineers use to make adjustments to race car suspension or to tire pressures. Since good & accurate tire "Needle Pyrometers" cost a couple hundred bucks, few individuals have them. Some think a simple IR gun from Harbor Freight is OK but all that does is give the approximate surface temperature of a tire which is always cooler than the important internal structural temperature. Rubber is an insulator so heat does not move through a tire structure from hot to cool very well so you can mislead yourself if you only use surface temperature. The IR gun is fine for conductive materials such as metal in a hub or brake drum.

Heat is generated at the molecular level not from belts rubbing against each other. This heat moves slowly from the hottest location (belt edges) to cooler surfaces. There is the surface of the air chamber and the surface on the outside of the tire.

The air on the inside of the tire gets warmed from the heat transfer from the inside surface of the tire. This air is also cooled by transfer to the metal wheel and the turbulence inside the tire means the temperature of the inflation gas (air) is fairly uniform.

The inside temperature is related to the outside temperature in that cooler outside temperature allows faster heat transfer from inside to outside so the inside temperature will be a little lower when the outside is lower but not in a 1:1 relationship.

Tire pressure will increase as described by Boyle's Law PV=NRT. I did the math proof in my blog post of March 13 2014 .

So after all that we are left with the facts that:

1. A tire generates heat based on deflection (tire inflation & load) and rate of deflection (speed)
2. More deflection due to more load or less inflation or both, results in more heat in the tire structure.
3. More speed means greater generation of heat. This is one reason tires have speed ratings.
4. If you lower the CIP you will generate more heat and this will hurt the rubber and eventually weaken it.
5. With sufficiently low inflation or sufficiently weakened rubber the heat will increase at a faster rate than it can flow out of the tire structure and can go into "run-away" increase which can result in a sidewall flex failure or "Blowout" due to shorter term low inflation or possibly a belt separation due to long term heating and weakening of the belt rubber.

I hope this clarifies and answers any additional questions.

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Sunday, August 30, 2015

Michelin Goodrich tire recall

Just heard about a tire recall which may apply to your pick-up truck or SUV.

Michelin Goodrich tire recall

NHTSA Campaign ID Number: 15T016  Synopsis: Michelin North America, Inc. (MNA) is recalling certain BFGoodrich Commercial T/A All-Season tire size LT275/70R18 125/122Q LRE, BFGoodrich Commercial T/A All-Season 2 sizes LT275/70R18 125/122R LRE, LT235/80R17 120/117R LRE, LT265/70R17 121/118R LRE, LT245/75R17 121/118R LRE, LT245/70R17 119/116R LRE, and BFGoodrich Rugged Terrain T/A sizes LT275/70R18 125/122R LRE and LT275/65R18 123/120R LRE.

 The affected tires may experience rapid air loss due to a rupture in the sidewall in the bead area. If the tire sidewall ruptures during use resulting in a rapid air loss, it can cause loss of vehicle control, increasing the risk of a vehicle crash. MNA will notify owners, and dealers will provide similar replacement tires free of charge. The recall began on August 24, 2015. Owners may contact BFGoodrich Consumer Care at 1-866-524-2638.

NOTE you will only get a notification if your vehicle/tire dealership filled in the registration card and gave it to you when you bought the vehicle/tires. AND you then finished filling out the card and mailed it in.

If you did not register your Michelin or Goodrich tires you can do so on-line HERE

Tuesday, August 25, 2015

What temperature for CIP "cold inflation pressure?

I occasionally see posts on the need to do an adjustment of your Cold Inflation Pressure ( CIP )when the temperature is not at some "standard".

Many times the "standard" is stated to be 70F or 68F. Neither of these are correct.

From a tire design standpoint CIP means when a tire has not been warmed up either by being in direct Sunlight or from having been run.
We are not talking about some chemistry lab experiment but real life. This is defined by the Tire & Rim Association, the organization that published the standards book for tire dimensions and recommended Load & Inflation for all kinds of tires, wheels and valves.
 These standards are primarily intended to provide "interchangeability" as we want to be sure that every 15" tire fits properly on a 15" wheel of the appropriate type. Or that the valve will properly seal against air leaks by having the hole in the wheel of the correct diameter.

Now you don't have to get all wound up with temperature probes or IR guns to confirm a tire has not been warmed up. Just follow the guideline that when checking or adjusting tire pressure to your CIP, the tire should not have been driven more than 2 miles in the previous 2 hours, AND that the tire has not been in direct sunlight or otherwise artificially warmed up in the previous 2 hours.
"Cold" really means when the tire is at the temperature of the surrounding air or what is called "Ambient" temperature.

So unless you are taking your RV to the Antarctic or to the Sahara desert you can use the above as a simple guideline. Even if I were planning a trip from the top of Pikes Peak to Phoenix in a single one day drive I would not worry about making adjustments based on expected temperature. Tires are designed to have a large tolerance for pressure increase due to variations in the surrounding temperature.

Remember the rule of thumb is that tire pressure will only change about 2% for every change of 10F so even going from 30F to 100F might only result in a pressure change of 14%. Now you would probably need to adjust the CIP the next morning before setting out but again you would set the CIP when the tire is in the shade and not driven on for a couple of hours.

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Tuesday, August 18, 2015

Is it time to consider buying tires "Made In China?"

My most popular post was the one back in Jan. 2012, "How-good-are-chinese-tires"

Recently I read a post that I thought some might find interesting on what some with strong sales background have to say about tires made in China, so I'm passing along this link from AutoGuide: "Should-I-buy-tires-made-in-china?" I consider this article to be a good, well-thought-out article on tires made in China.

I have also noticed that while many of the low-cost tires seem to have a warranty that ends about the time you pull out of the tire store or RV dealer's parking lot, there are a few offering 3- to 5-year warranties which make them, in my opinion, worth your consideration.

There are even a couple I know of that are offering 75 mph speed rated tires in ST-type sizes that appear to actually be real commercial-grade tires.

Now, please remember I have not personally conducted testing on many tires made in China so can only work with some limited data, but I do believe that there are tires coming out of China with acceptable quality in them. You still need to consider general availability and what you might need to do if you actually want to make a warranty claim. If you are buying on the Internet, then obviously you will not have a "brick & mortar" location you can go to to get service. You do need to figure the cost and hassle associated with having to ship a failed tire back to some location and what you are going to do about having a replacement available. This might entail the need to have a mounted spare on hand at all times. Just something to consider.

One final comment re the low cost ST-type tires from China seen on many trailers. When evaluating the tires you might see if the tires on the trailer are a brand that you can buy at retail or if they are only seen OE (original equipment) on trailers. If you can't find the tire at retail then there is a good chance it is a low cost "container baby" where the lowest cost per tire in container lots is the only performance criteria considered important by the importer or RV assembler.

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Tuesday, August 11, 2015

22.5 tire inspection. Confusing answer from dealer

Got this Private Message (PM) about sidewall "Bulges". Will keep it "private" redacting any identifying details but think there is a good learning experience for others here.

 Thanks for sharing your knowledge, and I do like your blog!

I have 5 1/2 year old xxxxxxxxxxxx Mich XZE* tires on our coach. No cracking, and have performed well.

I found sidewall 'bumps' on two tires ("Tire store" Tire Center gent, said they're not 'bulges', as they're so slight). One maybe 3/32" of a protrusion, the other much less. The "tire store" gent said they could be belts that are misplaced or broken. But, he also said the "*" XZE's have a thicker sidewall, and that the outer layer of the tire could have separated.

I know it's hard to give advice based upon a description, but, I wanted to ask your thoughts on the opinion given to me by this "tire store" gent.

He suggested that I monitor the size of the 'bumps' daily, and if they don't grow, he felt that they were safe to drive on. When asked if he would drive on them with his family, he said from what he could see, yes. He commented that the tire was so overrated for what it was carrying weight wise on my RV, that it was not working hard.

I've always thought that once a tire starts to break down, that it was at risk for a catastrophic failure?

The tire was not unmounted for inspection, but if it was a outer layer separation as he said it could be, how would they be able to see this?

Opinion? At 5 1/2 years of age, is it worth even considering monitoring and watching for growth? Or just replace and move on?

(I have a thread on Class A, asking for ride opinions between the XZA2 and the Cont HSL1 in 315/80R size. These are the two I'm currently considering to put on the steers. But, open for input on others to consider too!)

Hope you don't mind the PM, but, I was just a bit uncertain on which way to go.


Here are more pictures of the feature of concern. You can see the small bulge right above the "M"

Here is my reply
First off I do not feel that sidewall "bumps", "bulges" or "protrusions" occur because of misplaced or broken belts. Belts are under the tread not on the sidewall so I have to wonder what training, if any, the "gent" at "tire store" has received on tire construction or inspection procedures. Also not sure what he is talking about as the "outer layer" of the sidewall. In a TBR tire there is basically the thin innerliner then the body ply then the sidewall. So if he thinks the sidewall has separated then the tire has failed and should be replaced.

Now some fact based observations on sidewall bulges or outward protrusion vs depressions that are inward toward the air chamber and are indications of two completely different causes.

The inward depressions can occur once or twice around almost any radial tire. If you take a close look if full sunlight of smooth sidewall tires you will see depressions than might be about 1/4" to 1/2" wide in the circumferential direction. These are caused by the lap splice of body ply material that provides more resistance to the slight growth seen in all radials due to inflation. The depressions will run a radial direction from the wheel to the tread and seem to dispensary as you get near the tread or near the wheel. These are normal and I would only consider them minor cosmetic features of a tire.
An outward bulge may be 1/2" or as large as a couple of inches in the circumferential direction. The larger or more distinct the more concerned I would be about the durability of the tire. Usually bulges are the result of some impact damage done to the body cords that resulted in a few being broken due to shock loading.

Here is a blog post I did with pictures to help people understand.

Here is a post on an Impact Failure I had on my personal car

Now some with small features the eye plays tricks as to it being a bulge out or a depression in.  I have even seen instances of two depressions being close together such that the normal sidewall between the depressions gave the appearance of being a depression. The simple tool to use is a ruler or straight edge and to lay it across the area of interest. This will quickly identify if you have a bulge or depression.

What to do:
Review my blog posts above.
You might also find a different dealer. A simple Google for "Truck Tire Dealer Town"  where "Town" is a near-by larger community, should give you a number of options.
Are you dealing with a TCI  "Passenger/Light truck center" or a "Commercial Truck Center"  For 19.5 and larger size tires I would only deal with a Heavy truck Center.
You might also contact Michelin at their Customer Contact identifies on their RV tire page for a suggested location with people sufficiently trained in tire inspection to pass judgment on your tires.
you can tell them that your not happy with the inspection you got from "tire store" as they don't seem to understand the basics of tuck tire construction.

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Tuesday, August 4, 2015

Are you smarter than a tire dealer? Part 1

With apologies to the TV show "Are you smarter than a 5th grader"...

I sometimes wonder if RV owners are or at least need to be smarter than the average tire salesperson.

I bring this up based on a few recent observations and experiences. Let me give you some examples and then some suggestions to help you get the tires and service you want and need for your RV.

I have read a number of examples where RV owners had their tires inflated by a tire dealer only to later discover a variety of issues such as too much air, too little air, loose or missing valve caps or even loose valve cores. While I am sure that many dealerships want to provide good service, I think it important to remember that many times it is the "new kid" that gets the job of doing a pressure check and the on the job training may be done at your expense.
I would suggest that if you are going to have a dealer do tire inflation, it is in your best interest to provide the tire tech with clear instructions on the pressures you want. If you have more than a single inflation (fronts different than rears for example) maybe just an index card with a simple graphic along with the inflations you want will avoid confusion. You might even consider specifying a few psi higher than your real Cold Inflation Pressure or CIP so the next morning when you do your check with your Master Gauge you can let the pressure down which is always easier than needing to add a couple psi.
Also I suggest a quick walk around after the inflation check to be sure you have metal caps on all your valves. A light tightening twist may not be out of line to ensure you don't loose a cap on the way home.

Now the biggie Tire Buying.

 Next to going to the dentist, buying tires may be one of our least favorite activities in life. I do not expect to change your mind on this and turn the act of visiting a tire store something you look forward to, but I would like to offer some advice to make the task less stressful and possibly extend the time between visits so you have to go tire shopping less often.

Here is where some fact based knowledge can pay off in making the activity less stressful and might even end up saving you some money in the long term for I believe that a better purchasing decision will lead to lower probability of problems.

Lets start off by deciding if we are simply "replacing" out tires with more of the same or if we are "shopping" for tires that might deliver better performance, fewer problems or longer life.

Tire Replacement
If the tires you currently run have delivered satisfactory service, why would you think you need to make a change to a different size, type or brand? To me this would fall under the "It ain't broke, but I'm gonna try and fix it" approach. If your plan is to simply replace the tires you have with a newer set then you have it easy, simply shop for tires identical to what you already have.
When shopping I suggest you first go out and read the sidewall of your current tires. Note the Brand i.e. Goodyear, Michelin, Maxxis, Duro, Cooper etc. Next the type or design. This might be a name like "Marathon" or a number like "S637". Finally and maybe most important the COMPLETE tire size this includes the letters and numbers in front of and after the dimensional numbers and would also include the Service Description part, if any, that comes after the rim diameter. Service Description has two parts: Numbers for Load Index and a letter for the Speed Symbol or Speed Rating

For size something like "235-15" isn't correct and if that is what you tell the tire dealer, what you are really doing is sending the message that you really don't understand tires so an unscrupulous dealer may try and take advantage of you.
Technically an "LT235/75R15 107/110Q Load Range D"
is a different tire than an "LT235/75R15 Load Range D".

If you are not completely clear on this you might want to review THIS post that covers the differences for Passenger and Light Truck type tires.

Trailer or "ST" tires will have markings similar to LT type tires

Class-A Truck Bus Radials or TBR type and European commercial tires will also have size information similar to LT but with no letters in front and of course bigger numbers like "275/80R22.5 Load Range G". For TBR type tires the Service Description part is optional. If your current tires have a Service Description I would include that information when identifying the tires you want to the dealer.

You may find that shopping on the Interweb an exercise in confusion as I find many tires listed with incomplete or even incorrect tire information. Poorly designed web site may not be an indication of the competence of the dealership but it is not a good sign. This might be the first sign that you actually are smarter than the tire dealer.

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Tuesday, July 21, 2015

How to avoid tire failure and RV damage. And I had a tire failure!

A general comment on tire inspection and how it may be able to prevent RV damage due to tire failure if done properly.

There are three basic types of tire failures.

- The least likely is a sudden large impact with some object in the road. This is the least likely and is actually difficult to do. By this I mean to have a tire that is OK with no damage having been done due to excess heat, high load, low inflation or improper repair. It could even be a new tire. You drive over something like a Railroad spike or into a foot deep pot hole or over a 10" chunk of scrap steel that fell off a truck. It has to be large and you have to hit is just right for the tire to suffer immediate failure. I know from personal experience (doing a special test project of tire "Rapid Air Loss") that even driving over a piece of 2" pipe sharpened at one end and standing 2" up in the road with sharp end up doesn't always cut through the steel belts of a tire.  Yes you might run over something that cuts the tire but you would see it in the road and hear it hit but most of the time the air loss is not immediate. The good news about this type of failure is that it has a very low probability of happening. I would guess that fewer the 5% and maybe less than 2% of RV tire failures are of this type.

- Next is the belt separation. This is when the tire tread and belts come off the body of the tire. This is usually the result of tire aging and long term cumulative heat related damage that reduces the flexibility of the rubber to the point that rather than bending the rubber develops microscopic crack which do not heal themselves but will grow. Excess heat and tire aging can come from many sources. Even parking in direct sunlight with "tire protectant" spray does not lower the temperature of the tire. Excess heat can accelerate the aging or the tire rubber properties and drastically reduce the tire life. I would expect that if properly diagnosed this type of failure occurs 25 to 40% of the time. The good news is that with proper and frequent tire inspection this can be discovered and the tire replaced before it comes apart enough to cause damage to the RV. I did a blog post just on this topic "How do I inspect my tires" back in Aug 12 2014. You can Google the phrase and find a number of web pages on the topic but many simply are telling you to look at tread depth but this is not sufficient if you want to do a complete and competent inspection. My link included a YouTube video showing the inspection of a tire with belt detachment that has not come apart and the result of the "tire autopsy" I was able to perform. You can even see the separation between the belts in the above post.

- Finally there is what is commonly, and incorrectly, called a "Blowout". This is really a failure of the tire sidewall due to excessive flexing from running with significantly under-inflated ( probably below 50% of the inflation needed to carry the load. For Polyester tires (mainly ST and LT type) This heat due to flexing can be enough to reduce the strength by half and in extreme cases even melt the cord. For Steel body tires the bending of the steel can result in a fatigue failure similar to bending a steel paper clip till it breaks. This type of failure may be 60 to 80% of the failures on RVs. The good news is that if you run a TPMS you will get a warning of the air leak and hopefully you will not ignore the warning as too many do with other warning indicators on their dash, and take appropriate action which is to stop and pull over as soon as safely possible. Amazingly some people, even when verbally warned that they have a tire that is significantly under-inflated simply choose to continue to drive off. This has happened to me a number of times. As the saying goes "You can lead a horse to water but you can't make them drink".

So how doe this information help you "avoid" failure and RV damage. While nothing is 100% I bet you would like to be able to prevent 90% to maybe 98% of tire failures you might experience.

To do this I suggest that you run a TPMS and to get plenty of advance warning I suggest you set the warning pressure to be the minimum needed to support the load. Then your cold inflation pressure would be about 15% higher.

Next do a "free spin" inspection with lots of light. This is relatively easy with a trailer but harder to do as your axle load increases. You may even need the HD jack from a truck tire center and the spin balance machine to get that big 295/75R22.5 tire spinning at at least 20 to 30 RPM to allow you to see if there is "wobble" similar to the video in my post on How to I Inspect my tires" above. While the tire is in the air also do a slow rotation to inspect 360° of the tire tread as well as 360° of each sidewall looking for cuts and bulges. If any are found you should get the tire to a service center for a more thorough inspection that may include de-mounting the tire.

I believe that if you don't see any bulges or wobble and don't have any localized irregular wear spots in the tread you can be reasonable confident there is no large separation.

Remember nothing is 100% but if you make an effort you can significantly improve your odds of avoiding a tire failure.

Information to show you how this can work. Three weeks ago I was doing my annual 360° inspection. My tires are 7 years old so even though I know they have always been properly inflated (4 corner weights + TPMS from 2nd week of operation), I knew I needed to be sure all was OK. I discovered one of my duals had developed stress cracking from long term parking. This was a real surprise for me but it shows that even with the best of care rubber can get old and tires do need to be replaced.

  This tire was scrapped (I cut two slices from bead to tread to prevent its re-use by a "dumpster diver") as it still had lots of tread but I felt it should not be on the road.

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Monday, July 13, 2015

When did you last check the air in your spare

If you carry a mounted spare, it won't do you much good if it is flat when you need it.

I have seen some studies indicating that most spare tires have lost more than 75% of their inflation pressure.

Amazon has a kit.

Camping World has similar.

Friday, July 3, 2015

When is Minimum inflation the Maximum inflation?

Sometimes the information on inflating tires can lead to some confusion.  OK a lot of the time it can be confusing to many.

As many of you know I try and follow a number of RV forums and offer comments. I try and focus the comments to correcting serious or significant errors or misunderstandings, especially when Safety Related.

Recently there was some confusion about the Maximum allowable inflation for a tire. Some wanted to co-mingle some information from PSR or passenger car tires with information about large TBR, truck bus radials. The discussion then went way off track. Rather than limit my audience to those following that thread, I decided a blog post would be more appropriate. Also I wanted to be sure to have all the information up to date and accurate I contacted an "old friend" from the tire industry and he sent me this nice summary. With his permission I re-print it here.

First some definition of terms may be appropriate as "tire engineer speak" may confuse some.
"Seating pressure" this is the inflation needed for the tire beads to "pop" home against the wheel/
"FMVSS" these are various Federal Motor Vehicle Safety Standards. If you need some reading that will put you to sleep HERE is a link offered by NHTSA.
"PSR"  Passenger steel belted radials or the normal tire you find on todays cars
"TBR" Truck Bus Radial  as found on most Class-A RVs
"LTR"  Light Truck Radials 
"CIP" Cold Inflation Pressure

OK here is the nitty-gritty
"First, the max pressure to seat beads as a matter regarding the technician’s safety is 40 psi, whether passenger, light truck, or truck-bus.  This bead seating pressure is totally independent of the tire maximum operating pressure.

It is important to clarify the differences in sidewall markings of the tires you bring up:

PSR & LTR Tires (load range E or less):  Since FMVSS 139, these tires have sidewall markings indicating maximum load AND maximum pressure.  Maximum load means max [static] load, and maximum pressure means max [operating] pressure (cold).  With respect to the minimum pressure that carries the maximum load there is a difference:

·         Passenger Tires:  These tires are usually marked with a maximum pressure that exceeds the pressure necessary to carry the maximum load marked on the sidewall.  For example, the tire may be marked with 44 psi max pressure, but only requires 35 psi to carry the max load.

·         Light Truck Tires (load range E or less):  These tires are usually marked with a maximum pressure that is also the pressure required to carry the maximum load.  For example, a load range E tire marked with max 80 psi would need that same pressure to carry the max load.

TBR Tires (and light truck load range F and higher):  On these tires the sidewall markings indicate maximum load AT a certain pressure (the word “maximum” is not used in regards to pressure).  Maximum load means max [static] load, but the pressure is not the maximum operating pressure (cold).  This marking just follows FMVSS 119.  Essentially, the pressure marking is informative, simply telling the reader the pressure that is required to carry the maximum rated load.

However, for most practical purposes, on TBR tires the pressure marking is typically considered the maximum pressure recommended in the tire while in ordinary service.  Certain situations may permit cold inflation pressure higher than the marking, usually in consultation with a tire manufacturer for a specific product, application, and service.

Regarding load-inflation tables:  As long as you are looking at the right table, this is where you find the pressures needed to carry certain loads for a given tire type, size, load rating, etc.  Note that for truck-bus, you might need to make sure the tire is a “T&RA tire” or an “ETRTO tire” since the tables can differ, even though the size codes are the same (such as 295/75R22.5).  Also, a tire manufacturer may have unique load-inflation table(s) associated with certain tire models, sizes, etc.

If an operator is running at max load, and the pressure to do that happens to be max pressure, then yes, they need to be diligent.  But it is manageable, and they owe it to themselves and to others on the road to do so.  Pressure loss through permeation requires minimal adjustment approximately once a month.  For predictable swings in temp, set the pressure when it is likely the coldest, and try to consistently check it during those times, such as early in the morning before setting out.  No one is saying that everyone in all circumstances needs to set pressure to +/- 0.1 psi every morning, noon, and night with three hours of ambient cold-soaking before taking measurements.  I agree with you about reducing load; not just due to the tire influence, but also drivetrain/axle and chassis wear and tear, braking performance, fuel economy, etc."

So we see there are similar but different words on the sidewall of tires. Some have a stated Max cold inflation others do not. This is one reason why it best to have tire service done at a store that has the appropriate equipment and training to handle safe and proper mounting and inflation of the type tires you are working with. This does not mean you can't add 5 or even 10 psi to your tires but IMO if you need more than 20% of the CIP there is something wrong and you really need to consider having a professional inspect and re-inflate your tires. Inflating an improperly mounted, improperly repaired or damaged tire can injure or even result in death if not handled properly.
OK now back to our regular programming.
One other comment I have is that many times some think tire failure "Blowout" is caused by too high a pressure but this is essentially incorrect. Unless you have damaged the body ply cords, be they Nylon, Polyester, Steel or Rayon by over flexing and running significantly under-inflated, tires are designed to tolerate the normal pressure increase seen when running highway speeds at the approved load.

But if you have damaged or run the tires in overload or under-inflated for the actual load or perhaps at a speed higher than the tire rating you may have damaged the cord sufficiently that it has lost a portion of its strength so in that case even normal cold inflation may be too high. This is one reason any tire that has been damaged must be rendered un-usable or if it appears to be OK then inflated in a Safety Cage.

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Tuesday, June 23, 2015

Help It's hot and I need tires

That's the message I read on an RV forum.
Here is the pertinent background info.

   "I am having a real issue with Michelin tires.  I live in Las Vegas and there are 3 tire companies that carry Michelin tires.  The problem is they all tell me they are back ordered and have been for awhile.  They have no idea when they will get any.  I have a 40' 2008 RV that came with Goodyear tires and have serviced us well.  I just don't know what do do since I can't get Michelin tires which seems to be the tire to get. Should I settle for Goodyears that are in stock?  My other issue is we are going on a trip next week that we can't get out of and because of the extreme heat here in Vegas we are afraid that our old tires might just fly apart. What should I do?"


While I can't address tire availability from Michelin, you need to remember that there are generally considered to be 3 tiers of tire companies. Michelin, Bridgestone & Goodyear as #1 with the tires made & sold by these companies as being essentially the same  ie Firestone & Dayton ~ Bridgestone, Kelly & Dunlop~ Goodyear and Goodrich & Uniroyal ~ Michelin.

Now there are some minor differences within a corporation but many times the rubber compounds and reinforcement materials are identical or very similar. Tread designs may be a bit more advances in the Corporate brand and the top of the line tires may not have an equivalent in the 2nd brand  but for most people you will not see a difference in performance.

#1 tier have their own tire stores with many hundred nationwide.

Now Tier #2 would be tires made by corporations that have their own tire plants. These would be companies like Toyo, Pirelli, and others seen on this list. They may not have any company stores and jsut depend on large tire distributors to market their tires.

3rd tire would be companies that are not on the list above. These may actually be just sales companies the have other companies make lower cost product for them as "private brand" , Sometimes the same tire is made for a number of importers with only a name-plate change in the mold to differentiate the "brand" These companies seldom have their own stores but sell their products through wholesalers.

Check the tire warranty and I think you can get a good feeling for the real quality of the tires you might be considering. Are there lots of exceptions or if the warranty short could be a tip off that the seller isn't real willing to stand behind the products they are selling

Now to your concern about your current tires and the hot temperature.  It's kind of hard offering an opinion or suggestion on if you need new tires right away or not, but tires simply do not fail simply because it is hot outside. Excess heat is not good for long term durability but if the tires have always been properly inflated, never been punctures or run even a few psi low you should be OK for a while.

You didn't offer your actual age of your tires but they are probably 7 to 8 years old. You also failed to provide info on how you store your tires. Inside or out in the Sun? Do you have a lot or a little extra load capacity based on actual individual tire position weights? Do you run a TPMS and have never run lower than what is needed to carry your actual measured load. All of these items can contribute to making a suggestion to change your tires right away or suggesting that you can wait a few weeks or months.

If concerned about road or ambient temperature just drop the speed down. Don't run 70 when 60 will still get you there. Last Aug I drove Ohio to Oregon at 60 - 62 with no problem.

Can you increase your tire pressure without exceeding the tire or wheel max?

Where are you headed?  Have you checked to see if there is a large tire dealer at a future location that has tires for your RV in stock?

In the meantime I would suggest you go to a Goodyear truck tire dealer and have the tires inspected. Let them know your concern about the tire age and current hot temp in Vegas. Let them know your actual scale weights (Go to a local truck scale location first. There are a number around Vegas I'm sure)  and your normal cold inflation. WHile there ask if they would confirm the accuracy of your pressure gauge. If a stick type +/- 5 is about what I would expect. If digital (better) +/- 2 would be good. If outside these numbers you need a new gauge. Check my blog on tire gauges and how to have a reliable "Master Gauge" of your own for less than $15.
The tech should be familiar with the Goodyear tires you have so can offer first hand information on the condition of your tires.
Remember you can always get just the two fronts replaced as a failure there would be the greatest concern. With a TPM on the rear duals a failure would be less dramatic and you should get plenty of warning so you can safely pull over quickly before serious damage is done.

It would be nice to be able to offer more specific answer to his question but all to often people fail to provide important information that would allow more than a wild guess.

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Tuesday, June 16, 2015

Safety Recalls

The National Highway Traffic Safety Administration or NHTSA just made available a video to help people understand vehicle recalls.

Understanding Vehicle Recalls” gives a quick overview.

This website allows you to check if your vehicle or tires are under a recall.

If a safety recall is initiated, your manufacturer will notify you of the recall through first class mail and offer to fix it for free. If your vehicle is recalled, please call your local dealer as soon as possible to make an appointment for a free remedy. By fixing your safety recall, you have the power to save your life, and the lives of your passengers and other motorists.

Sign Up to Receive Recall Alerts via email alert.

Report Potential Safety Problem.  I have previously posted information on the importance of reporting tire failures to NHTSA. Just complaining while you sit around the campfire or venting on an RV forum may make you feel better but it will never result in action that could improve the quality of RVs or the tires that go on RVs. Reporting a vehicle or equipment safety problem to NHTSA is an important first step to get the situation remedied and make our roads safer. If we receive similar reports from a number of people about the same vehicle, this could indicate a safety-related defect may exist that would warrant opening an investigation. Report your vehicle safety complaints on

I am in the process of writing a post that will show that there is hope for RV owners. I am seeing an increase in load capacity  as well as an increase in speed ratings for trailer applications and will be covering this in depth next week.

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Thursday, June 11, 2015

80+ mph RV tires ?

Recently read a post on a forum where the question was asked about by-passing the speed limiter that was on the poster's Class-A unit as the poster wanted to drive faster than 80!

The general consensus was that this was not a reasonable speed in an RV and almost universally people knew that their tires were rated for 75mph or less.

On my trip from Ohio to Oregon last summer I noted that many interstates now had updated the posted speed limits from the old 55 to 65, 70 and as high as 80mph. While I "puttered" along in the right lane with my cruise set at 60-62 mph, I saw all manner of vehicles whiz past me, including many RVs, some of which were clearly exceeding the speed rating of their tires.

In March  I wrote about tire speed ratings, but this is a real safety issue with potentially both short- and long-term consequences. 



I wrote again in April on "How fast can I safely drive?"

First off, as a professional race car driver and police driving instructor, I think it would be unsafe and foolish to drive an RV in excess of 70 mph. A quick search of the internet finds numerous charts showing the effect of increased speed on stopping distance, with large RVs needing 40% to maybe 80% more distance to come to a stop as speed increases.

At 55 mph, you will "only" need 100 feet more than the length of a football field to stop; at 80 mph, it would take you the length of three football fields to come to a stop. While you might get lucky as you sit high above the traffic, have you asked yourself how you would feel after driving completely over a passenger car that can stop in maybe half the distance it takes you to stop?

BUT this blog isn't about general driving safety, as hopefully you have a good understanding of your vehicle capabilities, having done a practice emergency stop on a "closed course." I want to address the effect of speed on tire durability.

Tires have a speed rating. This is the speed at which a tire can be driven for a short time without failing immediately. For most ST type tires this is 65 mph. There are some special high load trailer tires that are only rated for 62 mph.  LT tires and TBR (Truck-Bus Radials) are rated for 75 mph in RV service. If you look at the side of passenger car tires you will see a "Speed Symbol" letter.
An example might be LT235/85R16 114/111 Q   with the 114/111 being the "Load Index" single and dual and the Letter "Q" being the speed symbol.

Many LT tires also have such a symbol but if you place a passenger tire or LT tire in RV service the manufacturer has lowered the speed rating to 75 max. If there is no Speed Symbol then the speed rating for LT tires should be considered to be 65 mph.

As I wrote previously, some ST tires may be rated with a speed number or symbol by the manufacturer. This number should be molded on the sidewall. I would not trust information that is just verbal from a tire salesman.

I just updated my "Links" post with information on an importer of ST type tires that has published the speed symbol for their tires as "L" which corresponds to 75 mph.
Here are some of the Speed Symbols and the corresponding max speed capability:
F = 50 mph              G = 55 mph        H = 60 mph        J = 62 mph     K = 68 mph     L = 75 mph

It is very important that you understand that all the above is based on a laboratory test done on new tires. If a tire has hit a pot hole or been repaired or been parked in the sun for months, then there has been some degradation to the tire's strength and I would not expect it to pass the same test requirements. In fact, if a tire has been repaired, it's in many pieces of literature that the tire looses its speed rating.

Another bit of information to remember is that running fast will increase the temperature of a tire and as I covered in depth in my post on tire covers: "Increased temperature causes continued and accelerated chemical reaction which "ages" a tire faster than when the tire is cool. A rule of thumb would be that the rate a tire ages doubles with every 18°F increase in temperature. We can see the result of old rubber on the surface. What we don't see is the more brittle rubber of the internal tire structure. As rubber gets more brittle with age it also looses strength." Running a tire at 70 rather than 60 will probably increase the internal temperature by about 18°F so every hour you are driving that fast is costing you two hours of tire life. Damage is cumulative and slowing down does not repair the damage you have already done.

Drive safe.  Slow down and enjoy the journey.

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