Tuesday, December 20, 2011

Why do so many trailer tires (ST) fail?

There is no clear answer, only speculation. Anecdotal information drives speculations into name calling and negative design confidence.
As everyday tire users we are spoiled. We don't suffer tire failures with our everyday vehicles. When we do they can almost always be accounted for. Most of us will go for many years without a single tire failure. Then we get an RV trailer and POP goes the tires.

The tires on our everyday vehicles are - in most cases - specifically designed for the vehicle they are on. They are quality graded for all sorts of conditions with tread designs to match the grading. Their load capacity has been derived from the maximum loaded vehicle with a 6% reserve left over which will seldom, if ever, be used. They are constantly in use so the built-in chemical compounds stay in action and degrading is held at the bare minimum. Most of them will wear out long before they will ever get old enough to be effected by degradation or age or both.

On the other hand the RV trailer also has tires specifically designed for their position. And that's where almost all of the similarity ends. Seldom has a tire design been scrutinized as often and with such detail as the ST tire. Almost all of the American manufacturers have given up on the trailer tire or have sent it to their off shore plants in faraway places like China, Vietnam, Korea, Taiwan or Thailand etc.

Most users that have had a ST tire failure or numerous ones are not going to like or agree with many of my analogies on this subject. The overwhelming evidence will support my stance but there are no official statistical findings to support what I say. But, logic always has a strong influence on many outcomes in the absence of other evidence.

In the absence of numerous recalls for the ST tire one must assume the design is sound and cannot, by itself, have caused the many failures reported against it.

Once the design is ruled out of the failure scenario  the cause must lie elsewhere. So, is there a single cause or a combination of causes? I like multiple causes over the single one. Of course any highly abused single cause can also be the culprit.

Here are my accusations. We overload our trailers. We speed with our trailers. We take a somewhat lackadaisical attitude about our trailer's tire pressures. We store our trailers for long periods of time - six months or more - with no regard for the tire's condition or pressures. The trailer may not even be level which causes tires on the low side to become overloaded for their entire time in storage. We don't balance or rotate the trailer tires. Sometimes the spare is
exposed to the elements for so long it explodes.

FastEagle

13 comments:

  1. I enjoyed your blog post! I lean towards wear and tear for tire damage. I use RV covers to protect them from a blow out or an premature cracking on my tires.

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  2. Having suffered one major tire failure which resulted in thousands of dollars of repairs I became anal about the speed I travel, (never going above 60mph) tire pressure ( check with every fill up and before I leave for my destination) and storage. I decided to replace my tires every 2 years regardless. Well, that wasn't the formula for avoiding tire failure. I just had another also resulting in damage with 2 year old tires , (they were slated to be replaced after this trip). These 2 failures were not only blow outs but in one case the complete tread separated from the tire exposing only the metal layer, it was if I had a retread on rather then a new tire. Years ago I had a 28ft enclosed car trailer for my construction business. It was loaded to the hilt, didn't move much during the year and I have to say never checked the tire pressure, I had that trailer for 6 years without one tire problem before I sold it. I just think the trailer tires of today are made rather cheaply.

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  3. Tire tread separations are probably the most common failure occurrence with RV trailer tires - any design. Go on your computer and do a search for RV trailer tire failures. It’s probably the most written about RV trailer tire failure scenario you will come across in your search.

    Whenever such failures occur the owner should make an attempt at recovering the tread. Tire forensic experts can determine the cause of the failure much faster with both tire sections in hand. But, an intact carcass will reveal most everything needed to determine the suspected cause.

    I’ve read a lot of finished reports on tread separations when involving RV trailer tires. There are a lot of factors that muddy up any conclusions a layman such as I might want to make. Damage to a tire’s inner liner allowing water intrusion into the carcass may be the most damaging factor for RV trailer tires because of the amount of time they often set without proper maintenance and inspections. Remember what I said, that’s from a layman’s view point.

    FastEagle

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  4. Hello Fast Eagle. I have read numerous forums regarding trailer tires to formulate a plan for replacing my 225 75R 15 LRD fifth wheel tires. The forums are long on opinion and bickering and short on facts. I have read your assessment on speed and overloading and agree with all of that. What I can't quite get over is the fact that so many of the RVer's seem to be so happy and trouble free after changing to LT tires. Do you have any explanation? (i.e. liars, way overtired) My plan is to purchase brand name ST LRE for a little more margin without needing to change wheels etc. I haven't had any problems yet on my two year old Akuret "china bombs".

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  5. For retiredoslacker;

    There are a lot of explanations for replacement tire longevity or the appearance of it. Usually replacements are stronger with increased load capacity. That in itself will/may add to its longer life expectancy compared to the Original Equipment (OE) tires.

    Most of the major RV trailer manufacturers have, at one time or another, in the past 10-12 years used standard Light Truck (LT) tires for OE fitment on a number of their models. At about the two year mark they found that the more expensive LT tires were experiencing very similar failure rates as the like sized Special Trailer (ST) tires. So they went back to the ST tire almost exclusively. There are a few exceptions in larger sizes starting with the LT235/85R16G tire manufactured with steel casings by numerous brand names.

    Airstream RV is currently offering Michelin LT tires as an option on their Eddie Bauer model. Of course the larger RV trailers with 8000# axles often have medium duty truck tires designed for low profile hi-cube operations.

    The bottom line is; Replacement tires are not going to have much traceable information to use for compiling any kind of information. Most people are not going to register them, probably because they’re serving in a misapplication fitment.

    FE

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  6. I have a different take on travel trailer tire failures.

    On my Rockwood 2604WS, the margin between the weight on the tires when fully loaded and the combined factory tire load rating is only 10lbs per tire. (This includes taking into account weight that is offloaded to the tow vehicle through the hitch.) So when sitting still in my driveway, my trailer if loaded to the GVWR is pushing the tires to the limit of their capacity. As soon as the trailer moves, almost anything will overstress the tires.

    One thing that will increase force on my tires is weight shift to the outside wheels on curves. I've calculated that my outside tires will be overloaded by 580lbs each if I drive 20mph on a curve that has an advisory speed limit (little yellow sign) of 20mph. This is an overload of roughly 30% and is conservative because advisory limits are not manditory and many drivers ignore them.

    Another thing that will increase the force on my tires is a cross wind. Federal high wind advisories are issued when wind speed exceeds 30mph for one hour. So at or below 30mph, there would be no obvious reason to stay off the road. I've calculated that a 30mph crosswind will overload my leeward tires by 309lbs each. This overload could continue for hours if I'm, for example, driving on I-70 in Kansas.

    I've also looked into the federal rules for testing of ST tires (FMVSS 109). ST tires are only tested up to 100% of load rating. They are not tested for overload. So there is no reason to assume that overloading on curves or in wind will be tolerated by my ST205/75R14 tires.

    I conclude that the factory tires on my trailer, and probably many others, are repeatedly and significantly overloaded in normal driving because the trailer manufacturers have allowed no margin for dynamic forces like wind or driving on curves. I'm very suspicious that this is a major underlying cause of many trailer tire failures.

    I'd be happy to share my math with anyone who might want to see for themselves.

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    Replies
    1. Crosswinds are something all drivers must take into account when towing a big tall box. Frequent stops to check tire temps is highly recommended.

      Tires are going to be built to sustain more than 100% of their load rating. If not, many of them would fail the tests. The public is not going to be informed of anything more than the authorized maximum load capacity lasted on the tire sidewall.

      All tires degrade as they are used. All damage is cumulative. The ST tires or any others used as trailer tires are going to degrade faster than normal when operated close to their maximum load and speed restrictions. ST tires fail sooner because the degrading causes them to be operated in an overloaded condition much sooner than tires with more load capacity reserves and speed restriction reserves.

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    2. ST tires are not built to sustain more than 100% of their ratings. FMVSS 109 only requires testing at up to 100% of rated load. There is no requirement and therefore no guarantee of what will happen at 101% of rated load.

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  7. After a little research on your trailer model I've determined that you have 2 3300# GAWR axles with tires rated at 1760# on each end of those axles. Not a lot of load capacity reserves but legal. Because of the way the regulation reads for trailer tire fitments the trailer manufacturers only have to provide the very minimum requirement.

    This is an excerpt from a NHTSA Q&A PDF: The FMVSS have requirements for the manufacturer to use proper tires and rims for the gross axle weight rating (GAWR) and the gross vehicle weight rating (GVWR). The manufacturer may determine the GVWR by adding cargo capacity (if any) to the curb weight of the vehicle as manufactured. The wise consumer, before purchase, will determine if the vehicle has sufficient cargo capacity to carry the weight of water, additional equipment (such as televisions, and microwave ovens), and luggage. The manufacturer’s certification label must show the GVWR. The GVWR must not be exceeded by overloading the vehicle. There is little the government can do to assist a consumer who has purchased a vehicle that has insufficient cargo capacity for its intended use.

    It's the GAWR for trailers. the rest is self explanatory.

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  8. Actually, my axles are rated for 3500#. And I haven't exceeded my GVWR or GAWR, both of which are static measurements.

    Yup. It seems that my trailer meets industry standards.

    My point is that industry standards are broken because they don't consider dynamic forces.

    If I load my trailer to its GVWR and somehow manage to achieve perfect balance, as soon as I tow it on a curve, the tires will be overloaded. It's only a question of how much is the overload.

    And, if I load well below the GVWR and GAWR, and tow on a reasonable curve, it turns out that the tires will still be overloaded because the tire load rating margin is so slim. I'm talking about reasonable usage in fairly ordinary circumstances that will still cause tire overloads.

    A product liability lawyer will tell you that it's not a good defense for the manufacturer to hide behind inadequate federal standards. This will lose in court if it can be shown that the standards are inadequate, which they obviously are.

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    Replies
    1. Any argument here cannot take sides. The regulations for tire fitments to RV trailer axles are very clear. They must support the trailer's certified GAWR, period. Testing has nothing to do with fitment. Tire construction (Passenger, Light Truck, Special Trailer, etc) is a consideration for the vehicle manufacturer.

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    2. Vehicle manufacturers must set GVWR & GAWR. They must also select appropriate tire/rim fitments for each axle's GAWR. They must also set a recommended tire inflation pressure that will insure the tires support the loaded vehicle.

      Axles are not always manufactured in load increments desirable for all fitments. The DOT allows vehicle manufacturers to set the vehicle's GAWR and certify it as appropriate for that vehicle. It is often misunderstood by vehicle owners and can cause their trailers to be overloaded.

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    ReplyDelete