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Wednesday, December 24, 2014

Tire Bulge. Defect? or Damage

Sidewall bulges can be difficult to diagnose. Sometimes it is even possible to misinterpret a depression as a bulge so lets start off today's lesson with clarifying the words.

According to  bulge means a "rounded projection, bend, or protruding part; protuberance; hump".  I think we can all agree that this is a sidewall bulge.

A depression would be the opposite, or "sunken place or part; an area lower than the surrounding surface". Sometimes I may use the terms "Bulge in" and "bulge out"just to be sure people have a clear understanding.
Look closely at this shot and I think you can see that this is a depression in the sidewall.
 Here are a couple of other shots showing sidewall depressions.

OK So now you are probably asking why are these two conditions in tires and are they defects or what? Lets step back for a moment and consider how tires are made.

The basics apply to all tires, be they small 10" or 12" as seen on micro cars or 22.5 or even large mining tires like this one.

In this post there are some links with videos showing the basic process of wrapping layers of fabric (or sometimes steel cord) that is in a sheet of rubber, around a drum. The place where the builder starts and stops has a "splice". Now the goal is to have a strong enough joint to keep the uncured rubber together till the tire is cured. In some constructions this means a small overlap of one to maybe 4 cords. If the overlap is larger than desired there is a doubling-up of the cord and this is what creates the depression. I know this is counter-intuitive but you need to remember that when a tire is inflated the rubber stretches and the textile cords stretch a slight bit. However if the splice is "heavy" or larger than desired the forces from inflation are resisted by twice the normal amount of cord and rubber so the stretch is less than in the rest of the tire. There is nothing wrong here other than a visual depression.

Now a bulge is just the opposite. If the splice is "open" or there are cords missing then that area will stretch out more as there is only sidewall rubber resisting the air pressure so the sidewall stretches out just like a balloon. A bulge from an open splice is noticeable as soon as the tire is inflated. If you see this on a new tire point it out to the tire dealer right away and confirm the bulge is below the level of concern for that make of tire. This will probably be less than a tenth inch above the surface of the rest of the tire and less than 1/2" wide. If larger I would request a different tire unless the dealer is willing to put in writing that the tire is safe.  Get a nice close picture of the tire for your records and be sure the bulge does not get any larger.

The other thing that can cause a bulge is broken body cord from some sort of impact such as a curb, pothole or from hitting something on the road. Here are a couple shots of a 22.5 that suffered an impact.

.One thing to point out how I know this was not a factory defect. I have yellow arrows pointing to the small amount to irregular tread wear. You will note that this level of wear is fairly uniform around the tire. If the defect had been in the tire from when new I would expect the sidewall bulge to affect the tread wear. Since it didn't, that indicates to me the break of the body cord is recent.

In case you are wondering what broken cord might look like here are a couple shots of broken Polyester cord from a smaller tire.

.I hope everyone now understands the difference between a cosmetic depression and a bulge due to a tire impact.

If you have a Bulge that looks anything like the examples above I would not drive on the tire. If we are talking about a high pressure tire (75 psi or higher) I would not even stand near the tire while waiting for service. A tire explosion can be damaging or even injure people.

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Wednesday, December 17, 2014

Cost of tires

Had a question concerning the cost of tires, which some think does nothing but go up, as it relates to the current downturn in the price of gas at the pump.

The argument was that since gas prices have gone down so should tire prices.

Yes it is true that a good portion of the "rubber" in tires is really synthetic which means the raw material is petroleum based. Today's passenger, LT or ST tires have very little if any natural rubber but as you move up in size there is an increasing % of natural rubber.  Some 22.5 size tires have natural rubber as a component but without access to the secret proprietary formulas I can't address the % which could range from 0% to maybe as much as 25% or more.
There is also the special high strength brass plates steel to consider along with numerous other materials such as Silica,
From Whikipedia we see
  • Natural rubber, or polyisoprene is the basic elastomer used in tire making
  • Styrene-butadiene co-polymer (SBR) is a synthetic rubber which is often substituted in part for natural rubber based on the comparative raw materials cost
  • Polybutadiene is used in combination with other rubbers because of its low heat-buildup properties
  • Halobutyl rubber is used for the tubeless inner liner compounds, because of its low air permeability. The halogen atoms provide a bond with the carcass compounds which are mainly natural rubber. Bromobutyl is superior to chlorobutyl, but is more expensive
  • Carbon Black, forms a high percentage of the rubber compound. This gives reinforcement and abrasion resistance
  • Silica, used together with carbon black in high performance tires, as a low heat build up reinforcement
  • Sulfur crosslinks the rubber molecules in the vulcanization process
  • Vulcanizing Accelerators are complex organic compounds that speed up the vulcanization
  • Activators assist the vulcanization. The main one is zinc oxide
  • Antioxidants and antiozonants prevent sidewall cracking due to the action of sunlight and ozone
  • Textile fabric reinforces the carcass of the tire

What hasn't been addressed is the research, manufacturing and transportation costs. With the ever increasing pressure for improved fuel economy, smooth and quite ride as well as, long wear and all season performance the R&D efforts are continually increasing.

I think it is important to remember that oil price at the pump is a poor reflection of the real cost of the commodity especially when most of the materials are  bought based of future delivery so current day to day variations have little affect of the price of oil someone is willing to commit to 5 months or a year in the future.

Another thing to look as is the profit margin of the tire companies over a multi-year basis.  For example I believe Goodyear profit in 2013 was about 3% of sales income.

If you want the nitti gritty check this web site and you will see the Return on Assets ranges from negative 6% to plus 5%

 Here is a good article on the topic.
and another that focuses on the raw materials.

Now please remember I may be a tire engineer and I even play one at RV Conventions but I am not a financial advisor and as we all know past performance is no guarantee of future performance.

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Thursday, December 11, 2014

Tire recalls and Registration

Here are some details on the recent RV tire recall:

 NHTSA Campaign ID Number: 14T015 
Synopsis: Dynamic Tire Corp. (Dynamic) is recalling certain Towmax STR tires, size ST225/75 R15 manufactured June 15, 2014, to October 14, 2014. The affected tires may have the Incorrect Load Capacity and Inflation Pressure Stampings. Thus, these vehicles fail to comply with the requirements of the Federal Motor Vehicle Safety Standards (FMVSS) 119. The misinformation on the label could lead a driver to over-inflate the tires. Tire over-inflation may increase the risk of a tire failure which can increase the risk of a crash. Dynamic will notify owners, and dealers will replace all eligible tires, free of charge. Owners may contact Dynamic customer service at 1-905-595-3593.

The details are that 17,000+ Load Range D Towmax tires with DOT serial ADB4GPD2414 through  ADB4GPD4214are subject to the recall and are to be replaced FREE of charge.

One bit of information that many will skip over is the part where it says Dynamic will notify owners. While this is standard language in recall notices it overlooks a major problem. Just how is Dynamic supposed to know the owner's name & address?

According to Federal law all DOT tires are supposed to be registered and that information is supposed to be entered in a big database to enable future contact in case of a recall. The problem is that according to various studies only about 17% of tires sold by dealers have the necessary registration forms completed and sent to the registration authority.

Do you know if all your tires have been registered? If not then you will probably never know about a tire safety recall.

        Note this is not limited to Towmax brand tires but applies to all of your car, truck, trailer or motorhome tires.

Confirm that your RV Dealership registered the tires on your trailer or motorhome. If you bought your car or truck new from the company dealer the tires are probably registered.
 You might start by asking what their policy is. You may find some confusion or hemming and hawing on the part of the dealer, I would take as indication that they did not do the task they are supposed to do by law.

Car and truck dealers may do a better job but we all know what can happen if we "assume" someone is doing the job they are supposed to do.I would see nothing wrong with using the on-line registration process below,just to be sure.

If you bought tires directly from a tire dealer you should ask them what their policy is. Some will have clear statements such as we see from Tire Rack. BUT if you get that uncertain response there is a good chance the tires you bought were not registered. Probably the smaller the tire or RV dealership the lower the probability the tires were registered

You can do the job yourself at    or simply Google Tire registration and see if your tire brand has a sight just for registering your tires.

Please don't be concerned that this is some "Big Brother" conspiracy. I have never heard of this information being used for any purpose other than notification of a recall.

Finally if you have changed mailing address you might want to update the tire registration. Remember you will need the full DOT serial including the date codes for each tire.

If in doubt on how to read your tire serial number, reviewing THIS post will help.

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Monday, December 8, 2014

Match Duals... Does anyone really do this?

I believe that sometimes people understand that there are suggestions and recommendations concerning the proper care and maintenance of tires but all too often they just don't bother to follow the published guidelines as they feel it may be too much work or some guidelines are simply put out to get people to buy more tires.

Let's look at one example. I have previously covered the importance of "matching" dual tires by measuring the Outside Circumference (OC) and ensuring that each pair are within 3/4" for this measurement. You can read THIS post and THIS one for more details. But is this practice followed by truckers who may put 100,000 miles on their rigs in just a year or so? I think this might help you believe that the practice is followed.

Here are a couple of pictures I was able to capture at a stop-light.

As you can see from these pictures, this driver has matched the level of wear on the front pair of tires. Now this isn't absolute proof that the OC was matched but given the relatively even wear rate of truck drive tires it's reasonable to assume the change in tread depth results in a similar change in OC.

You want to match dual tire dimensions as if one tire is significantly larger than the other it will be forced to carry more load than the smaller tire. This will result in higher operating temperature which is not good for long-term tire life.

While measuring tread depth and doing some calculations may seem reasonable this practice ignores the reality that all tires "grow" in use so a new tire and old used tire will actually measure different if you do an actual OC measurement than if you just do calculations based on tread depth measurement done to the 0.01" accuracy.

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Monday, November 24, 2014

RV tire reference links. Load / Inflation tables etc

Based on posts I see on various RV forums it appears that some RV owners are having difficulty finding the appropriate technical information on their tires. As a result sometimes they post questions such as "I have a XYZ RV with ABC brand tires what is the correct inflation for my tires". If you are a frequent reader of this blog I trust you can see that much critical information is missing and any answer that says "Use QQ psi because that is what I use on my RV" is not much better than a wild guess.

I have decided to assemble links to tire Load & Inflation tables for the "major" brands of tires likely to be found on RVs. Now I know that there are many tires out there that are not made by or for the major tire manufacturers that have been selected by the company that assembled some RVs so this is not a list of each and every tire out there. If you have a tire not identified from one of the manufacturers I have listed, please send an email (address posted in the About Roger info on right side of this blog) and I will endeavor to update this list. Unlike most blog posts I plan on updating this post when new or additional information becomes available so you might want to Bookmark this page to your list of Favorites.

Note: I will use the term "TBR" for Truck Bus Radial and this in general means tires with 17.5, 19.5 and 22.5 rim diameter. "LT" of course means Light Truck and "ST" stands for Special Trailer. "P" or Passenger type tires would only be on passenger vehicles or very small trailer.

Sometimes it is difficult to know who actually made your tires. I have seen tires with the brand name "GT" which is obviously not the name of a tire company but simply a name used for marketing a line of tires. If you do not know who or where your tires were made HERE is a web site that will allow you to use the first two characters of the DOT serial molded on the tire sidewall to learn the facts. For example if the DOT serial on your tire was   4DHLABC4513  you would look uo the "4D" and discover the tire company to be BRIDGESTONE/FIRESTONE NORTH AMERICAN TIRE, LLC.  and the plant location to be Morrison Tennessee, USA, with a manufacturing date of 45th week 2013 or the week of Nov 3 2013.
If the first two characters were  4V you would discover the tire company was actually CHONCHE AUTO DOUBLE HAPPINESS TYRE CORP., LTD, TAIYUAN CITY, SHANXI, China.


Bridgestone RV application info.
While this company does not appear to actively market to RV owners they do have tires that will fit and work on many types of RVs that use LT or TBR type tires. This web page has general information on RV applications and a "how to guide" to help RV, travel trailer, mini-bus, van, light truck and ambulance owners learn how to properly weigh their vehicles and maintain their tires". The page also has a worksheet to help owners to properly weigh and calculate the correct minimum inflation needed for their unit. Much of the information on the web site is general in nature so is of value to many RV owners. Here is the Load Inflation chart in download PDF format for RV size tires made by Bridgestone. This brand is sold and serviced through both company stores and independent dealers.

Continental USA
This company has a line of smaller "commercial" tires based on European designs aimed at the Utility/Van market in addition to both LT and larger TBR size tires,  Some of these tires might fit trailers including larger 5th wheel trailers and come in 14", 15" & 16" rim diameter. NOTE these tires have sizes like 225/70R15C LR-D. The "C" after the rim diameter stands for "Commercial" and is a European background. Do not confuse these commercial tires with LT type. The sizes may be similar but the loads,  inflation and even some of the dimensions are different.
TBR size Load Inflation tables starting with 17.5" diameter can be found here
LT & European Commercial type tire Load Inflation 

Dunlop is a subsidiary of Goodyear Tire & Rubber Co.
They have a selection of LT type tires. This brand is sold and services through both Goodyear company stores and independent dealers. I could not find Load/Inflation tables specific to Dunlop but would expect that the Goodyear charts should line up 100%.  

Firestone is a subsidiary of Bridgestone Tire Co.
Like their parent company, Firestone does not actively market to RV owners. They do have their own line of LT and TBR type tires. You can download their Data Book HERE. This contains technical on both current and many discontinued tire lines along with numerous pages of tire, wheel and vehicle technical and safety related information. Load / Inflation tables for Firestone brand tires can be found in both the Data Book and downloaded separately HERE. They also have a page of general tire information and links HEREThis brand is sold and services through both company stores and independent dealers.

This company actively markets tires to the RV community is ST, LT and TBR type tires. They have a web site specially designed for RV owners with numerous links to pages with supporting technical information on "Tire Selection" and "Care & Maintenance". They have four videos featuring a now retires tire engineering friend of mine, Tim Miller as he explains various concepts of proper tire use and care in the RV market. I definitely recommend that everyone in the RV community watch these videos. If you want you can go directly to their Load & Inflation tables and learn about your tire capacity if you have this brand.  This brand is sold and services through both company stores and independent dealers.

This smaller tire company has a line of tires for RV application covering  LT and TBR application. I find they have a number of heavy duty LR-G and LR-H tires in 16" and 17.5 diameter that may solve some heavy load issues that some RV owners seem to struggle with. These tires are sold through independent dealers and I could not find any company owned store information of on-line Load/Inflation information. Info from them indicated "Hercules Tire follows the guidelines published by The Tire and Rim Association. " so you can look at the tables used by Goodyear, Bridgestone, Firestone or Michelin.

This company was founded in 1967 and has a variety of different type tires. For the RV market they focus on ST and LT including small commercial type tires. You can review their web info on ST type tires including their Load Inflation tables HERE.  The information on their Commercial and LT products can be found HERE. I do note that they have a 5 year warranty on their trailer tires unlike many of their competitors that have only 12 month or less. These tires are sold through independent dealers and I could not find any company owned store information

This is one of the two major tire companies that focus on the RV Motorhome market. Their Load/Inflation numbers are sometimes confusing as they sometimes show the load for a axle rather than individual tires so it is very important that you read the numbers and table headings closely. Remember when selecting the inflation needed for your tires based on the actual load you need to select the loads on the heavier end of the axle. All tires on an axle should have the same inflation (i.e. based on heavier end) and you still need to add at least 10% to the minimum inflation specified for the load for your Motorhome. While most of the inflation ratings are the same as seen for Goodyear or Bridgestone there are a few exceptions so this is another example of you needing to confirm the ratings of the tires IN WRITING before you make your purchase. 
You can find general information on Michelin RV tires HERE. There are links to Load & Inflation tables HERE.

Private Brands
Many of the smaller tire companies are in reality just "Private Brand" marketing companies. They do not design, engineer or manufacture tires themselves but simply place large volume orders from other manufacturers. Many times these companies can offer lower prices since they do not have the overhead of design or testing staff and facilities but this means that if you are trying to get technical information form the company you may end up talking to a "customer service" person with no actual tire experience. They also do not have company stores so if you have a warranty claim you may have to return the tire to the location where you made your purchase or sometimes it will be your responsibility to ship a failed tire to some service location many states away.

Private branding is just a marketing plan and is sometimes used by Major companies. Goodyear makes and sells Kelly brand tires. Firestone made Dayton brand. This is why it is important for you to read the DOT serial to learn who really made your tires. In some cases a marketing firm may have one size made by tire company ABC but a different size made by company XYZ. Other times the marketing firm might have 10,000 tires of a given brand and size made at one location but the next batch could be made at a completely different location or tire company. This "flexibility in manufacturing could man that the performance or reputation of a "brand" of tires may depend on which size or even what date of manufacturer we are talking about.


Trailer Owners need to remember that they need to run the inflation on the tire sidewall to minimize the damage done whenever turning. You can refresh your understanding by reading THESE posts.

WARNING to Trailer Owners.
For the most part you will find that brands not listed here will follow the US TRA published Load Inflation tables as used by Bridgestone, Firestone & Goodyear.  BUT I have run into a few instances where the RV trailer assembler and the tire distributor "played games" and have adjusted the load capacity upward just enough to meet the legal requirements for the GAWR to be equal or less than the total capacity of the tires. These loads are not in the Industry Standards and means you are stuck with the size, LR and brand tires as supplied by the assembler or you will not be able to carry the load specified in the owners manual or on the placard affixed to your trailer. This is one major reason why you should ask to see the tables for your individual tires and compare them to the industry standards otherwise your tire replacement options will be limited to a single tire.

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Sunday, November 9, 2014

Is monitoring tires "Rocket Science?"

I get asked this question quite a bit. I think that after reading various posts on tire inflation and load, some people want to complain a bit and are hoping to use the excuse that it is too much work to monitor tire pressure every travel day.

Here is an example from a trailer owner:

"I've noticed that 50 psi cold at sea level at ambient 65F is 54-55F at 6,000 to 7,000 feet.
  While touring should I deflate to 50 psi cold at 7,000 feet if I'm hanging around there for a day or two

I am hoping that if I share my personal experience, it will provide a down to earth view on the topic that some want to turn into "Rocket Science"

I just finished a two-month cross-country trip.  Ohio > Oregon > Seattle  > Calgary, Canada > Yellowstone > Ohio in my Class-C MH with LT type tires that are 7 years old but have always been covered whenever parked for more than a couple of days, Always running inflation about 15 psi above what is needed for actual max load based on 4 position scale weights that are confirmed to have not changed significantly each year with a trip across CAT scales.
 Fastest I ever run is 70 mph but most of the 7,400 mile trip was with cruise set at 62mph. In other words, the tires have had a good life with good care.

Elevation ranged from about 25' at Olympic Nat Park to 8,000'+ in Rockies. Morning temperature ranged from 33 F to 94 F. I have TPMS (both internal and external) so I am able to constantly monitor both pressure and temperature.

I adjusted the tires once during the trip. I think I needed to add from 1 to 4 psi in the 6 tires. Since I run a nice inflation cushion of +25% I don't get all bent out of shape when the cold inflation is off by 3 to 5 psi from my goal.

You don't have to make the task of monitoring inflation a big deal. While I may set my pressure to +/- 0.5 psi, you certainly don't need to be that fanatical, and I would consider it completely acceptable to be +/- 2% for  the average user as long as the "goal" cold inflation has an appropriate safety margin.

With TPMS I simply hit the button a couple times a day and get a real time reading of tire temperature and pressure. Yes, the temperatures vary and so do the pressures, but unless I see a sudden drop in pressure and there have been no external changes such as a sudden rainfall or one side constantly hotter than the other after spending hours with one side in full sun, I just do not worry about it.

Relax.  Let your TPMS monitor your tires and enjoy the scenery.

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Tuesday, November 4, 2014

Goodyear RV tire Load / Inflation calculation

Had a request for assistance of how to calculate the proper inflation to run on a set of Goodyear  G670 RV 255/70R 22.5 tires
 on the Motorhome. The owner was a little confsed by the charts.

Here is what I did based on the AXLE weights provided by the owner. Maybe if you have been a little unsure on how to do the calculations this post will help.
While it is always better to know the actual loading on each corner of your motorhome, I know that not everyone can find a local facility that can weigh individual positions or they hav not attended a large RV event where RV Safety & Education Foundation provides the service so hopefully this will help until the time you learn your actual loading.

He said he had the coach weighted at a CAT SCALE facility in California. The axle weight is the only weight he has so far.

The front axle weight is    7,580 lb
The drive axle weight is  15,760 lb
1. Calculated individual tire loading
   7,580/2= 3,790
15,760/2= 7,880 per side

2. Applied 5% factor for not having actual axle end weights
  3,790 x 1.05 = 3,980
   7,880 x 1.05 = 8,510    Divide by 2 to get individual tire loading 8,510/2 = 4,255#

3. Go to Goodyear RV tire page

4. Downloaded the Load Inflation Table.

5. Find the 255/70R22.5  (pg 3)

6. Look up the Single load that is equal or above 3,980 and find 4,190 at 80 psi

7 Add 10% to that inflation  80 x 1.10 = 88 psi. 

8 Looked up the Dual load equal or above 4,255 and found 4,275 @ 90 psi
9 added 10% to that inflation  90 x 1.10 = 99 psi
10 You now know the absolute minimum inflation to ever see on your TPMS  80/90 F/R

11. You know your "Goal" or "Set" pressure for each day of travel is 88/99 F/R

If you ever drop below 84 Front or 95 Rear you should add air. I would not let air out unless the COLD pressure exceeded 93F or 104R

The extra 10% inflation is so you do not have to chase your tire inflation around with day to day temperature & pressure changes.

Remember you need to be sure you do not exceed the cold inflation molded on the sidewall of your tires or the max inflation rating for your wheels. If you find yourself calculating pressures that exceed these ratings it means you need to put your RV on a weight loss program.

You can use this step by step post as a guide for learning the correct Cold Inflation for your tires.
You can learn more by reading the posts on my blog with Temperature, Pressure or Inflation as "Labels" I do not expect you to remember all the information but if you review the posts you will probably remember that I wrote something on the topic of interest in the future so you can then go back and review to answer to whatever your questions is.

 This is NOT the method for you to use. The above is ONLY for MOTORIZED RVs.

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Picture from Goodyear website. I figured they would not mind since I am helping their customers.

Tuesday, October 28, 2014

What is a good Quality Tire? (part 2)

In Part 1
I outlined that for the purpose of our discussion “Quality” meant "Conformance to a Performance Specification". We also looked at how different reviewers may have different expectations for the Quality or performance attributes of a set of tires. This time we will show how not all tires are intended to be of the same Quality since different applications and different customers have different objectives.

The customer, and this does not mean the retail buyer but the company making the volume buying decision, establishes the performance specification and hopefully also establishes the relative importance for each evaluation point on the list of features in the specifications. If the customer is a vehicle manufacturer they have in mind certain positioning in the market for their vehicle so they want tires that help them meet their sales and marketing goals.

For cars this is easy to understand how handling is more important for some applications while mud traction is more important for others. Obviously the performance goals for a tire for a Corvette will be quite different than the performance specifications would be for a Jeep, but the consumer magazine made the erroneous assumption that all tires of the same size were designed with the same goals in mind and that the relative importance of those goals should have matched the personal preferences of the magazine test crew.

I would suggest that they failed to consider that people contemplating the purchase of a set of tires might not have identical needs or expectations from a new set of tires.
I will provide an example. Suppose you own a 5 year old pick-up and at 60,000 miles you got good wear from the first set of tires. You plan on keeping the truck for another 5 years and expect to drive a similar amount so you are looking for a set that delivers the lowest cost per mile as the "Best" option. But what if you only plan on keeping the truck for 9 months to a year? Why would you want to spend $800 on a set of tires when a $360 set will still have many miles left when you sell it.
For a vast majority of people in the market for tires, the price is the most important feature they want or maybe that is all they can afford. Some tire dealers focus on the segment of the market that is price driven rather than performance driven so for them, low price is the Number One characteristic they specify when making purchase decisions while they say they will accept any performance for other characteristics or quite frankly just seem to not care.

While meeting all regulatory tests is always a given, tire design engineers are sometimes challenged to rank low cost as their number one objective.  To meet this goal of low cost, the engineer may select lower cost tread compound and trade off lower wet traction to get the lower cost compound. They might also design a narrower tread which needs less rubber and less steel (lower cost) at the sacrifice of wear and max handling. They might even design less tread depth to get lower cost while giving up some snow traction.
So with cost maybe 55% lower that a top of the line performance tire they have clearly met the specification. How would this not be the better quality tire when the objectives are taken into consideration? In the real world if you can't sell the product, it doesn't make any difference how good someone, who is not making the decision to buy or not buy, thinks it is.

In the RV market, where as far as I know there are no direct tire performance comparisons done by vehicle assemblers, be they for a 45' diesel pusher or a 13' pop-up trailer. I believe there may only be three criteria. Ability to carry a certain load (i.e. size & Load rating), tire availability and price. In some cases they may even ask the tire company to make a slight increase in load capacity to avoid having to buy a larger (more expensive) tire. Some tire companies with no retail presence in the US market and knowing they will not be confronted with the cost of adjusting the tires because they offer no or very short warranty are willing to "tweak" the claimed load capacity so they can make the sale even if the load capacity is outside established industry standards and it makes finding an appropriate replacement tire a significant problem for owners of the RV or it actually results in lower long term durability. After all if you can make the sale of a few thousand tires and know full well you will never have to address the cost associated with adjusting or replacing a failed tire why worry?

 Sometimes the ability of certain tires to meet some expected level of performance creates misleading ratings. In one case I recall, a tire was rated both exceeds expectations and fails to meet expectations. The fact is the same tire was applied to both a Luxury vehicle and a base model from the same vehicle manufacturer. The issue was that the end user, who was doing the evaluation, had different expectations based on the luxury level of the car so rated the tires on the Luxury car better than the tires on the base vehicle despite the fact that the  tires were identical. So what value was that customer rating for people making a buying decision?

After reading this I hope you can understand the problems associated with using a magazine review as a reasonable method of learning the quality of a product. I also hope that you understand that getting a proper reading on real quality of any given tire will require that you do some homework and ask probing questions.

I hope by now you understand the problem with talking in general terms about "Quality". Also that the quality of one specific product made or sold by a company may or may not reflect the quality of other products they sell.
Reading reviews on "Tire Quality" has always been a hot button issue for me as I can quickly see that those doing the evaluation seem to not have a clue of how or why certain tires are designed for certain applications or to different objectives.

I will also offer a suggestion that when buying your next set of tires or RV you request a minimum of four year warranty on manufacturing defects and a three year Road Hazard Warranty. The Road Hazard Warranty will avoid disagreement on what caused the failure in the first place. I would also suggest that if if you are buying a set of tires it would make your case stronger if you are able to present weight slips showing your RV is not overloaded.
Now this will cost you a few dollars more per tire (maybe 15%) but I would wager that some tire or RV retailers will simply refuse to offer such a warranty.

 Could their refusal be based on their knowledge that the tires or RVs they are selling have a high probability of suffering some sort of failure during the first few years of use?
Maybe the dealers know the real quality of the products they are selling.  I know of at least on large tire chain that is happy to offer an extended warranty of their tires but the fine print excludes RV use. Have to wonder why.

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Friday, October 17, 2014

What is a good Quality Tire? (part 1)

Simple question that is often asked on various RV and car forums.
The problem is that I seldom recall anyone providing a clear definition of what they mean by the word "Quality".

If we look at Wikipedia we find the following:
    Quality Assurance, methodology of assuring conformance to specifications
    Quality (business), the non-inferiority or superiority of something
    Quality (philosophy), an attribute or a property
    Quality (physics), in response theory
    Quality factor, or Q factor, characterizes a resonator's bandwidth relative to its center frequency
 and others.

A quick look at RV reviews in magazines, finds the word "Quality" used quite often, but I do not recall seeing any evidence, cited by the authors, of said "Quality" of one RV being any better than another. On the contrary if we use length of warranty as a measure of overall quality I would suggest that in 2014 most RVs have quality comparable or worse to 1971 Pinto or Vega cars and many of us remember just how bad they were and the low quality of vehicles produced by "Detroit" till "Japan" beat the pants off US manufacturers, much as Korean car companies are doing now with their 5 and 10 year warranties.

Since this is a blog on tires, let’s limit ourselves to that topic. Even here there are obviously different uses of the word. A recent consumer magazine purported to present some observations on the quality of a group of passenger type tires. The definition of what the author meant was not clearly stated but can be inferred by the importance of certain performance characteristics as measured and ranked by the author. If a tire performed better for one specific characteristic such as tread wear, it was judged as being of better quality than a tire that did not wear as well. I would argue that this is an overly simplistic approach and can easily be misconstrued by readers just as a claim of "better build quality" in an RV review is meaningless if the author does not define what they mean by quality or they fail to present any supporting evidence.

With my background as a tire design engineer for a major tire manufacturer for 32 years and after working in the "Quality Assurance" department for 8 more years, I would like to offer some observations on how the term "Quality" is used in the tire industry. This is a complex topic so it will take more than one blog post but unlike some of my blogs there will be few technical terms used and the few I do use will be clearly defined.

After all I want to make this a "Quality Article".  :-)

Let’s start with a definition of the word "quality" in this post as   "Conformance to Performance Specification".

So a tire that meets or exceeds more "measurable" features as identified in its specification, would be considered to be of better quality than another tire that did not measure up as well for all of the same set of specifications. So what might a list of specifications include? One of the first tasks a design engineer has, is to ensure they understand what the customer wants.

Lets look at a partial list of what might be presented to the engineer. Some performance specifications are very clear such as:
"Pass every government Regulatory test by at least the margin established by company statistical margin as published in Standard Practice".   This quality standard is a must-do. The Pass/Fail levels are published and easily measured using standard tests with conditions for speed, inflation, load, and distance set down in test manuals.

Some other performance specifications are relatively easy to measure so the engineers know if the tire they designed passes or fails to meet the spec and by what margin they pass or fail to meet that particular goal. Some examples of these objectives might be:
"The tire is to weigh no more than 32.5#."
"The High Speed rating will be no less than 75 mph as measured on Society of Automotive Engineers test ABC".
"Rolling Resistance Coefficient (RRC) shall be 0.234 or lower on SAE test XYZ". ( RRC is a measure of fuel economy)
"Cost level shall be no higher than 90% of the reference tire as measured by corporate cost dept."

Others specifications are a little or a lot harder to quantify such as subjective performance
"Steering response shall be judged better than the reference tire".
"Noise shall be better than the specified reference tire".
Part of what makes these performance specs hard to quantify can be seen by looking at the noise evaluation "report card". Some vehicle companies have 10 or more different noise features they may consider important with terms like "Braking Growl", "Expansion Joint Slap", "Smooth Pavement Sizzle" and similar. Even Steering Response is complex with both "On Center Feel" and "Linearity" being a few of the items being evaluated for steering response. We don't need to go into the details of these evaluation features as that would be a post topic unto itself, but you can see these items may be difficult to rate as they are all subjective.

One challenge for the engineer is to get the vehicle evaluator to rank order all of  these various performance characteristic. Many times what we get is "They are all important" so how would you judge the conformance to specification if tire X was rated a +1 for "Expansion Joint Slap" while being rated equal in all other categories to the referenced tire but tire Y was rated a +1 for "On Center Feel" while being rated equal in all other categories to the reference tire? Which tire is the better Quality tire? I think the obvious answer is that despite claiming that all characteristics are "equally important" the evaluator really does have a preference and uses that preference to give the edge to one of the two tires being evaluated.

So why is this all so important? Well in the example of the consumer magazine rating the quality of some tires better than others I think they missed the point that not all tires are designed or even intended to meet identical performance specifications.

Next time we will look at why all tires are not designed to the same Quality Standard and what you can do to try and get the Quality you want in your tires.

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Tuesday, October 14, 2014

Should you reduce pressure when driving on "Hot" Roads?

I got this question and thought that others might be wondering about the same topic.

Jim K asked

 Message: I will be traveling in the desert for the first time and I am
wondering if I should reduce the tire pressure before I go. The hot road will
increase the pressure and I am afraid of damaging my tires.

Hi Jim,

No you don't have to worry about hot roads.
IF you run the correct cold pressure

Now you didn't say if you have a standard RV trailer or a Motorhome so I will give you a summary for each application.

Trailers: You should set the Cold Inflation to the pressure on the tire sidewall. If you look at the sticker on the side of your trailer you should find the tire size, type, Load Range and pressure recommendation from the manufacturer. In almost all cases the recommended inflation is the inflation on the sidewall of the tires.
Have you confirmed you are not overloading any of your tires? Simply guessing or looking at the tires is not good enough you need to get the trailer on a scale and at a minimum get the total load on the tires. Now you can't assume the load is equally distributed side to side or axle to axle Measurements of thousands of trailers suggests you need to assume at least 53/47 to 55/45 split axle to axle and split side to side so you need to calculate the heaviest load based on an estimate of 27% to 30% of the total being on one of the 4 tires. A better method is to get individual tire loading. You can learn more HERE.

Motorhomes are a bit different than towables. Here you need to get the "corner" loading as the side to side difference is affected by the placement of things like generator, water tanks, refrigerators etc. The Front Rear loading is obviously different and for most motorhomes the number of tires on each axle is also different. You can use the information on your placard but a better method is to get the actual tire loading and then using Load/Inflation charts establish the MINIMUM cold inflation then add 10% to get your Cold Set inflation. THIS post has some info and a link in it.

Bottom Line

When tires are designed, we know that some vehicles will be driven on hot roads. Tires will normally run +20°F to +50° above ambient. You should run a TPMS to get warning of air leak due to puncture. If you are driving in the USA you should have no problems.
Most TPMS also have a high temperature warning that is set for 155°F to 160°F. If you get a warning at this temp but the pressure is above your set pressure by about 10%, simply slowing down should lower the temperature. If that doesn't work you can still stop for 10 minutes while you do a walk around to be sure nothing unusuall is going on.
If you are traveling to Saudi Arabia, the Sahara or Australian outback then we need to take some additional steps and precautions.

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Wednesday, October 8, 2014

Retread on RV? You may end up with "Blowout" or Tread Separation.

Lately I have seen the question of using retreads on motorhomes crop up more frequently. I previously discussed this in February 2012, but it seems we need to revisit the topic.

The technology of retreading tires is well developed and when properly done the owner of the retread tire can expect more miles of problem-free usage. The key is "PROPERLY DONE," and "more miles"  but not more months.

The process of retreading really has two separate components. One is inspection and the second is the re-vulcanization of tread wearing rubber onto the previously used carcass.

The second step is relatively straightforward with new tread rubber being applied and cured to the carcass. I included a video at the end of the post for those interested in the details.

The problem area and technically more difficult part of the process is the complete and proper inspection of the carcass and the preparation of the carcass for the process of applying the new tread wearing rubber. In my opinion this is where most problems or mistakes occur.

The type tire and its service plays a major part of its "retreadability". In general car tires may be retreaded one time, some Light Truck tires once, Truck tires one to three times, and aircraft tires up to 12 times.

Why such a large difference? The primary reason is the service and maintenance a tire receives in its first life. Tires for aircraft usage do not have pot-holes or road trash to contend with and have tight control on the load and speed limits they are expected to operate under. They do not get driven over curbs and they are maintained by trained and licensed mechanics per published service schedules.

It is well documented that as a group, RV tires are more likely to be overloaded and or underinflated than any other type of tire. Also maintenance is not always done in a timely manner or with properly trained service personnel. The end result of this is that the carcass and belt components are much more likely to have been damaged during their first life. This damage is hard to detect without the use of expensive equipment such as X-Ray and Holographic or "Sherographic" examination similar to what we see in this video.

While all the above provide some information, the more fundamental issue  on why RV tires do not get retreaded is the age of the rubber itself. In the normal process of retreading we are just replacing tread rubber that has been worn off rapidly due to high mileage or, in the case of aircraft tires, high rate of wear. These tires are usually worn out in a year or two.

Many RV owners know that tires have a limited life with different applications, generally being limited to 3 to 7 years with a suggested max of 5 to 10 years service depending on the specific type of tire and service.

I believe that those asking about retreading the tires on their RV are simply assuming that it is the tread rubber that is the only part of the tire that is getting old and are maybe thinking that with a retread they will be getting a few years more "life" from  their tires. The reality is that it is the rubber around the steel belts that is of most concern for having over-age rubber, and this rubber is not replaced during the retread process.

Unless you drive your RV 100,000 miles and wear off the tread in a year or so, the idea of retreading will not gain you tire life. After a more normal 50,000 to 70,000 miles in 5 to 7 years, the carcass has been exposed to too many pot-holes, too much UV and Ozone, and too many curbs to be damage-free either on its surface or in its structure. While it may be possible to replace the tread of the tire, the clock for the max life of the tire does not reset when you simply replace the wearing surface of the tire, or even if you do a "full cap," which covers the aged sidewall and tread.

Background info HERE

Video on the Retread process 

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Sunday, October 5, 2014

Is it "Safe" to add air to your tires?

Got a question I have never heard before but thought I would share it and the answer with you as there is some safety related information to be gained.
Leih P.           asked
Just met an RV owner who was told by a Discount Tire salesperson that it was too dangerous for anyone to add air to a tire that was on the coach, as the risk was too great.  Apparently, from the rim or the tire exploding.  Even they weren't allowed to add air unless the tire was in a cage. 

Having to take the vehicle to a service center every time one needs air sure won't promote maintaining proper inflation.  Is it ok for the owner to check and maintain proper pressure, regardless of the tire size?

Thanks,  Leigh
I replied,
Yes, Leigh, you can add air to your, passenger car, boat trailer, light truck, Class A, B or C Motorhome or RV trailer or dolly. It is even OK for you to add air to your wheelbarrow tire or lawnmower tires. :-)
Now having said that, there are a few times when the use of a cage is advised
1. I would consider the use of a safety cage as MANDATORY for initial inflation if covered by OSHA Regulations   i.e tires larger than "LT" or tires on multi piece rims 

2. You should also use a cage when re-inflating any tire that had been run flat or suffered a puncture and lost more than 20% of its air.

Basically running a tire when low by 20% or more, can damage the body cord. On tires with steel body cord such as most Class-A type this can result in broken body cord which can result in an explosion when the tire is inflated. Tires damaged due to puncture should also be re-inflated in a cage.
I think the salesperson at the tire store misunderstood some of his training. My suggestion is to ask to speak to a manager. If you get the same advice on always using a cage when adding a few psi to a tire then I suggest you find a different tire dealer.
I do mention the use of a cage in this post.

I have contacted Discount tire but have not heard back yet. I believe the salesperson has some of their training information mixed up as I know of no regulation or even suggestion that simply adding a few psi to a tire that is already mounted and almost fully inflated needs to be done in a safety cage.

For those not sure what an Inflation Cage looks like or what it does here is a short video  from Ken-Tool doing an OSHA test.

One final comment. I did once receive a passenger tire for inspection that had exploded after being repaired. In this case the tech had damaged the tire when dismounting it. This is why I suggest that a safety cage or at least some type of restraint be used when re-inflating from 0 psi after a repair.

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Saturday, September 27, 2014

Consumer Report on tires made in China

Found this link on a new report from CR.
The tires tested were not ST type tires but the observations still apply.
The author thinks "Chinese manufacturing will follow the historical trend of Japanese and Korean brand tires, which were disrespected at first but eventually became good values in the eyes of the consumer".

I agree. I believe the current problems many are having with China made tires comes from the selection process done by the Trailer assemblers. To me it appears that for many, their #1 criteria is their initial cost. Since they don't have to worry about warranty costs some may be thinking that as long as it is round black and has the correct load capacity to meet DOT requirements it's not their problem if the RV owner has tire problems.

The challenge with tire failures is separating the "Root Cause" for a failure and learning if it is service related (overload, under-inflation and or over-speed)  or if the failure is a design or manufacturing quality problem. Too often RV owners forget that running a tire under-inflated a few months before the actual failure is the primary cause of the failure.

While on vacation I met a 5th wheel owner and of course the talk eventually turned to tires. He admited having tire problems in the past so claimed to be paying more attention to his new RV and its tires. The problem was he also admitted to having towed the trailer with only 35 psi in the tires but since he has now inflated the tires to their more proper 80 psi he was certain all was OK.

After a little more discussion it was obvious he was not receptive to the possibility that he might suffer a failure in the future because of his past actions.

I think the BOTTOM LINE on the CR report is that "some" China made tires do not perform as well as tires made in other countries. HOWEVER there are also "some" China made tires that are competitive with the rest of the market.

Monday, September 22, 2014

Do you have a Dolly behind your RV?

Many people choose to tow their 2nd vehicle "4-down"  i.e. with just a tow bar. Some choose to load their vehicle into or onto a trailer and others choose a "dolly" where only one axle of the 2nd vehicle is on the road and the second axle is on the dolly as seen in this picture I shot in Wyoming.

Now this post is not about the advantages and disadvantages of these three methods of towing a 2nd vehicle along on your travels but specifically about ensuring the tires on the dolly are the correct size and have the proper inflation to help you minimize tire related problems.

I'm going to take a different approach than you might suspect. Many times I start off by suggesting you get the individual tire loads and then consult tables. This time we can do a simplier method.
1. Look at the size tire that is on the vehicle axle that is to be on the Dolly.  In the above case it is a P235/75R15
2. Check the Tire Placard which is usually on the driver door jam. In the above case the inflation suggested by GM is 32 psi
3. Confirm the load rating at that inflation on the OE size tires. In this case 1940# @ 32 psi
4. Confirm the tires on the Dolly are rated equal to or higher than the tires on the axle on the towed vehicle.
In the above case the tires are LR-D and at 65psi are rated for 1984#.

Logic would suggest that since the vehicle manufacturer has staff engineers with the specific duty to properly set the inflation pressure on the vehicle it would be wise to follow their suggestion unless you have specific load information to allow you to set the tires on the dolly at a different pressure.

There is one problem. The owner of the above dolly insisted that the tires only needed 35 psi as the dolly bounced too much when inflated to 65.

Have to wonder if he will remember our discussion when he has tire problems in the future.

Thursday, September 18, 2014

Do you want to change your RV's wheels?

by Roger Marble

Here are some things to consider regarding changing the wheels on an RV.

For most RV owners, the wheels that came with the RV when new should work just fine. If you are running the original size tire and have confirmed you do not need to increase the Load Range of your tires to carry more load with a higher inflation, there is no reason to change your wheels, unless you have damaged one.

Now, if you want to change the look of your unit and switch to special chrome or aluminum wheels, then there are a number of things you need to consider:

What is the maximum load capacity of the new wheels?

What is the rated inflation of the new wheels?

Are they the same width and flange contour? This means the official size is identical, such as 16x7J. Note the letter is the shape of the area that contacts the tire. You should not change letters such as changing from a J to a K. One is not better than the other, but tires are designed for a specific flange shape.

Finally, if you run duals, then the "offset" dimension is very important. If you go smaller, your tires may rub, which could cause a problem.

All of the dimensions and ratings need to be stamped into the wheel or in writing from the manufacturer. I strongly urge you not to just take the word of the person selling the wheels.

If you think you need to change the wheels because you are changing tire size or rating to carry more load, you need to work closely with the supplier to be sure you are not overloading the axle, springs or other suspension components, the dimensions of the new wheels will properly fit the hub and bolts, and the offset will not allow the tires to rub.

Tires intended for dual application have specified clearance called "Dual Spacing," so be sure to confirm that dimension from the tire manufacturer before you go wheel shopping.

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Thursday, August 28, 2014

Strange wear on front of Class-A

Jim said:  "I attended one of your programs at the (FMCA) Redmond rally.  It was most interesting, and it convinced me that you may be the one person who has the background to identify the cause of my issue.  I’ve shown the photos to about 4 different dealers of Goodyear RV tire dealers and I’ve gotten 4 different answers.  I’ve also sketched the phenomena for the service manager at Josam alignment in Orlando, and he says it’s just typical of Goodyear tires, with no way to correct the situation.  It’s also been identified as “rivering,” which has been the subject of numerous posts on RV forums.
My coach is a 2011 34’ Newmar Ventana, on a Freightliner chassis.  I have had the coach weighed and, based on weight plus a safety factory, run them at about 85 PSI cold.  The deeper wear groove at the first groove happens on both the inside and the outside of both front tires, but not on the rear duals.
If you would be so kind as to respond with your thoughts it would be most appreciated.
 Jim S,
 Summerfield, FL (but currently on the road)"
Here are the pictures Jim Sent

 First I have to say, I wish everyone sending pictures of a tire condition took as good pictures as Jim did.
Well lit and close enough to clearly see the condition in question.
Anyway, here was  my reply:
" Jim,  Glad you enjoyed the seminar. Yes that is classical "Rivering". This is not something that only happens to Goodyear tires but is also seen on other brands. Its also not seen on all Goodyears either. It is a combination of tread pattern (design) and the selection of components and materials for the tire specification and the suspension characteristics of the vehicle. We design engineers do work at avoiding it but it is something that doesn't normally show up in our accelerated testing early in the design process so sometimes we can not "fix" it.

In my opinion, it is not a safety concern, but just a wear issue.
The best thing you could do is to swap out the two fronts for one of the set of duals. Now you do need to confirm the OD of the two tires going on as a set of duals is within 1/4".  The best way to confirm that is to measure the Outside Circumference while fully inflated and confirm the OC is within 3/4" of each other. Do the measurement before any tire dismounting is done to save $.
I don't know what wheels you have and sometimes you need to swap wheels sometimes not when moving from front to back.
I did a post or two on my blog and even a YouTube video on RVTravel channel on the topic and importance of matching duals. Just select from the list of "labels" displayed on the right side of my blog page for all the posts concerning DUALS.
Normally "Big Rigs" do not need tire rotation but this is one of the few times it is the correct course of action.

Hope this helps."

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Friday, August 22, 2014

How to weigh your RV for free

If you live in or travel through Oregon you can check the load on each axle and even get an approximation on your individual corner weights. I did this myself last week.

There are many truck scales across the state that are open and the electronic scale are left on after hours. You simply drive onto the pad and read the total load for that axle on the display panel located on a post about 40' ahead of you.

Now if there are no trucks using the scale you may be able to simply swing around or back up and get just the right side tire loads for each axle. With those figures its easy to subtract and get the approximate load on the left side positions.

See it in this picture where I am getting the weight on my Right Rear duals.

I say "approximate" as unlike the scale set-up used by RVSEF there will be a slight tilt away from the scale pad but I would think you should be within a couple percent of the actual side-to-side load distribution. I am pretty confident that most of you will have figures that are closer to the actual side-to-side weight distribution than just assuming you have a 50/50 side-to-side split on each axle.

With the individual corner loading you can then use the published Load/Inflation tables from your tire manufacturer company to learn the MINIMUM inflation you need based on the heavy side loads. Then simply add 10% to that inflation number for your "inflation margin" and you should be good to go. At least till you get on real, properly set-up individual RV corner weight scales.

Now I admit I do not know which other states provide this safety service to motorists, truck and RV owners, but for folks on the far west coast this is a great deal, at least till you are able to get the actual corner weights of your RV, or individual tire loads for trailers, confirmed by RVSEF.

If you know of another state that has scales available to the public as Oregon does, please post in the comments below as this information will help your fellow RVers


Locations with scales
This post relates to Motorized RVs NOT Towables. Trailers have SPECIAL considerations for setting the inflation that I cover in THIS post.

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Tuesday, August 12, 2014

How do I inspect my tires?

Got an email the other day asking about inspecting tires. This blog and many others will tell you that you should do a thorough inspection annually and doing the inspection becomes more important as times goes on.

The problem is, few know even the basics of proper tire inspection. For some it's only looking at the tread to be sure there is some tread pattern available. Others will bend at the waist and look at one sidewall to inspect for large cracks.

Well, sorry to say that doing a proper tire inspection is a lot more involved. You will need to get down on the ground, you will get your hands dirty and you will need a good bright work light. A dim, old style flash light doesn't provide either enough light or uniform lighting to allow a good visual examination. So lets start with the tools you will need. I suggest a rug or old blanket so you can lay down and even scoot part way under your RV to see the back side of the tire. For lighting a work light with at least 75 watt rating. As a low cost alternative if you don't already have a work light is the inexpensive LED light similar to THIS one or even THIS one. Note the low costs for these lights. A pair of thin gloves. You need to be able to feel bumps and bulges on the tire so thick leather work gloves like these

 will not do.I know that many have disposable thin, Latex or Nitrile gloves they use when handling their holding tank hose and that type or similar will work fine to help keeping your hands cleaner as tires are very dirty and rubbing your fingers across the sidewall will transfer oils, waxes, dust and dirt to your fingers.
Finally don't forget safety glasses. Dirt can drop from under the RV onto your face or when you are removing objects from the tread they can pop out and hit you.

We need to be consistent and thorough in our inspection as we need to cover 100% of both sidewalls and 100% of the tread. This also means that after you have inspected all your tires you will need to move the RV a couple of feet so the portion of the tread that was on the ground can be seen. Depending on your RV, there may also be areas on the inside sidewall where the tire is too close to the frame or other component which prevents a clear view of that part of the tire and this may require a couple of small moves. When going under your RV be sure the engine is off, the transmission is in Park and you have blocked the wheels from moving either direction.

The following applies to all tires. If you have a towable there are some extra steps you NEED to do and we will cover them later.


1. Tread. You are looking for nails, screws and other items lodged in the tire. Sometimes you will find rocks wedged in parts of the tread pattern. It doesn't hurt to remove them using a screwdriver as sometimes stones can "drill" into a tire causing damage. I would not use a knife or other sharp tool. If you find a nail or screw in the tread, it is possible that the object goes all they way into the air chamber and if removed may cause an air loss. If for example you find a screw you might start to remove it but if you get more than 1/4 to 1/2" loose and the screw is still in the tire I would screw it back in and seek service as you don't want to lose air by completely removing the screw if you are not a a location where your tire can be easily be changed. Making this decision takes some thought to avoid making the problem worse.
While looking at the tread see if the pattern looks uniformly worn both across the tread and around the tire. Non-uniform wear may be a sign of an alignment issue and in some cases are an early sign of a structural problem internal to the tire like THIS,

or it may not be serious and is just cosmetic.

If you see some localized wear and want it looked at by a tire dealer it helps if you make a notation using the letters and numbers on the sidewall for reference. An example might be "Local wear on Right Front, inside shoulder of tread, starting at number 3 clockwise to letter G".  Giving a dealer this guidance will do two things. One it will save them time in locating the area of concern and two it will let them know you have done a thorough job of inspecting tires so they are less likely to ignore you and more likely to treat you as a knowledgeable customer that knows something about tires. This is a lot better than telling the dealer "The tread on the front tire looks strange".
While we are still looking at the tread we also want to note for more detailed inspection  any cuts that are deeper than 1/16" in the grooves.

2. Sidewalls:  This applies to both inner and outer sidewall. First do a general inspection for cuts or punctures. Punctures in the edge of the tread and down to the wheel should NOT BE REPAIRED. Some people may claim to have done a satisfactory sidewall repair but there is just too much flexing for a repair to last. There are published GUIDES that show the only location (in the tread) where a repair is acceptable. This applies to ALL BRANDS of tires.  Any cut where the body cord is visible means the tire is scrap and should not be used. Next we want to find bulges. You want to feel for bumps and bulges using your fingertips and gently slide around the complete surface of both sidewalls of the tire. If the frame prevents this then you need to identify where you could not feel the sidewall so you can finish that part of the sidewall after moving the RV. Bulges can be a sign of broken body cord. I recently did a POST on broken body cord on one of my personal tires.
Depressions however are probably OK as for tires with multiple ply such as most LT and ST type tires this is just a small overlap where extra material is located. if in question just note the location as mentioned above
and ask a dealer to confirm.

Trailers: Tires on towables seem to have a much shorter life than tires on motorized RVs like Class-A, B or C. Part of the reason for this is the unique and higher structural loading placed on these tires during any turning. The sharper the turn the higher the stress is on the tire ply. This loading is working to tear the tire apart. These forces can lead to separations which ultimately can lead to tread and belts being thrown off the
carcass and in extreme cases a rapid loss of air when the belt separates. TPMS will not provide warning of a tread separation so the only tool available to RV owners is a thorough visual inspection.

The good news is that many times these separations can be discovered by doing a "free spin" inspection as seen in THIS video. At the beginning, you see that the wheel is round and shows no side to side movement. Then we see the tire as it wobbles side to side and even is out of round. This tire has failed and must be replaced at once. Here you can see when I did an "autopsy"

we discovered the belts are almost completely separated on this tire. To do a "free spin" you must get the tire up in the air so it rotates freely. Thus can be done with a jack or even one of the ramps that will raise one side of the trailer high enough as seen in THIS video. This is just one example.
As you can see there is some work involved but doing a thorough inspection may prevent serious problems later on down the road. You will also find that after doing a few tires you will become more knowledgeable about this important safety item on your RV. your tires.

NOTE Repair Guide link fixed 7/5/2019

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