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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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